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The health and psychological consequences of cannabis use chapter 7

National Drug Strategy
Monograph Series No. 25

7. The psychological effects of chronic cannabis use

A major concern about the psychological consequences of cannabis use
has been the possible effects of its chronic use on psychological
adjustment in general, and its impact upon motivation and performance
in occupational and social roles in particular. There have been two
variations on this concern depending upon the age of the cannabis
user. Among adults, an "amotivational syndrome" has been described, in
which chronic cannabis users become apathetic, socially withdrawn, and
perform at a level of everyday functioning well below their capacity
prior to their cannabis use. Among adolescents, the concern has been
about the effects of heavy cannabis use on motivation to undertake the
educational and other psychological tasks that are an essential part
of the transition from childhood to adulthood. The evidence for each
of these adverse outcomes of heavy cannabis use will be considered
separately, beginning with the effects on adolescent development,
which have understandably provoked the greatest concern, and prompted
the most research.



7.1 Effects on adolescent development

The effects of heavy cannabis use on adolescent development are of
special concern for a number of reasons. First, adolescents are minors
whose decisions about whether or not to use drugs are not
conventionally regarded as free and informed in the way that adult
choices are (Kleiman, 1989). Second, adolescence is an important
period of transition from childhood to adulthood, in which regular
cannabis intoxication may be expected to interfere with educational
achievement, the process of disengagement from dependence upon
parents, the development of relationships with peers, and making
important life choices, such as whether, whom and when to marry, and
what occupation to pursue (Baumrind and Moselle, 1985; Polich,
Ellickson, Reuter and Kahan, 1984). Third, the age at which drug use
begins has implications for subsequent drug use and health and
well-being. Early initiation of cannabis use predicts an increased
risk of escalation to heavier cannabis use, and to the use of other
illicit drugs. It also means a longer period of heavy use, and hence,
an increased risk of experiencing any adverse health effects that
chronic cannabis use may have in later adult life (Kleiman, 1989;
Polich, Ellickson, Reuter and Kahan, 1984). Fourth, since adolescence
is a time of risk-taking, the use of any intoxicant, whether alcohol
or cannabis while driving a car, increases the risks of accidental
injury, and hence of premature death (Kleiman, 1989; Polich,
Ellickson, Reuter and Kahan, 1984).

The type of evidence that initially excited concern about the effects
of chronic cannabis use on adolescents came from clinical case studies
in which bright adolescents' use of cannabis escalated to daily
cannabis use, and the use of other illicit drugs, leading to declining
social and educational performance, as evidenced by high school
drop-out, and immersion in the illicit drug subculture (e.g. Kolansky
and Moore, 1971; Lantner, 1982; Milman, 1982; Smith and Seymour,
1982). In some of these cases, the syndrome remitted after the
adolescent had been abstinent from cannabis for some months (Meeks,
1982; Smith and Seymour, 1982). Nonetheless, the evidence was largely
anecdotal and so of limited value in making causal inferences about
the contribution that cannabis made to the development of these
outcomes. It did not, that is, permit a decision to be made as to what
extent cannabis use was a symptom rather than a cause of personality,
or other psychiatric disorders, or a form of adolescent rebellion
against parental values.

The concern about the adverse effects of cannabis use on adolescent
development in the late 1970s prompted a number of large-scale
prospective epidemiological studies of the antecedents, and to a
limited degree, the consequences of adolescent drug use (e.g. Kandel,
1988; Kaplan, Martin and Robbins, 1982; Newcombe and Bentler, 1988).
These studies have attempted to tease out the contributions of the
users' pre-existing personal and social characteristics from the
specific effects of drug use. Some of these studies have also
attempted to examine the impact of illicit drug use in adolescence
upon a number of social and personal outcomes in early adult life
(e.g. Kandel, 1988; Newcombe and Bentler, 1988). The most important of
these studies are reviewed below.



7.1.1 Is cannabis a gateway drug?

A major concern about cannabis has been that its use in adolescence
may lead to, or increase the risk of using other more dangerous
illicit drugs, such as cocaine and heroin (DuPont, 1984; Goode, 1974;
Kleiman, 1992). The most popular evidence for this hypothesis is the
fact that the majority of heroin and cocaine users used cannabis
before heroin and cocaine. Such evidence is weak. In the absence of
comparative data on the prevalence of cannabis use by non-heroin
addicts we are unable to decide if there is an association between
cannabis and heroin use. Even if there is an association, alternative
explanations of its possible causal significance have to be evaluated
and excluded (Goode, 1974).

There is now abundant evidence of an association between cannabis and
heroin use from a series of cross-sectional studies of adolescent drug
use in the United States and elsewhere, including Australia. In the
late 1970s and into the 1990s in the United States there was a strong
relationship between degree of current involvement with cannabis and
the use of other illicit drugs such as heroin and cocaine users.
Kandel (1984), for example, found that the prevalence of other illicit
drug use increased with current degree of marijuana involvement: 7 per
cent of those who had never used marijuana, 33 per cent of those who
had used in the past, and 84 per cent of those who were currently
daily cannabis users, had used other illicit drugs. Current cannabis
users were also likely to have used a larger number of different types
of illicit drugs.

Cross-sectional data on drug use among Australian adults in 1993 have
also shown that those who have tried cannabis are more likely to have
used heroin, and the greater the frequency of cannabis use, the higher
the probability of their having tried heroin (see Donnelly and Hall,
1994). In the 1993 NCADA survey of drug use in Australia, for example,
the crude risk of using heroin was approximately 30 times higher among
those who have used cannabis than those who have not (even though 96
per cent of cannabis users had not used heroin) (see Donnelly and
Hall, 1994).

The relationships between cannabis and heroin use observed in the
cross-sectional studies have also been observed in the small number of
longitudinal studies of drug use. In one of the first such studies
Robins, Darvish and Murphy (1970) followed up a cohort of 222
African-American adolescents identified from school records at age 33,
and interviewed them retrospectively about their drug use in
adolescence and young adulthood, and their adult adjustment. They
found a higher rate of progression to heroin use among the young men
who had used cannabis before age 20.

These early results have been confirmed and elaborated upon in the
extensive research on adolescent drug use by Kandel and her colleagues
(e.g. Kandel et al, 1986). These investigators have identified a
predictable sequence of involvement with licit and illicit drugs among
American adolescents, in which progressively fewer adolescents tried
each drug class, but in which almost all of those who tried drug types
later in the sequence had used all drugs earlier in the sequence
(Kandel and Faust, 1975). Typically, psychoactive drug use began with
the use of the legal drugs alcohol and tobacco, which were almost
universally used. A smaller group of the alcohol and tobacco users
(although often the majority of adolescents) initiated cannabis use,
and those whose progressed to regular cannabis use were more likely to
use the hallucinogens and "pills" (amphetamines and tranquillisers).
The heaviest users of "pills", in turn, were more likely to use
cocaine and heroin. Generally, the earlier the initiation of any drug
use, and the heavier the use of any particular drug in the sequence,
the more likely the user was to use the next drug type in the sequence
(Kandel, 1978; Kandel et al, 1984; Kandel, 1988).

This sequence of drug involvement has largely been confirmed by other
researchers. Donovan and Jessor (1983), for example, found much the
same sequence of initiation, with the variation that when problematic
alcohol use was distinguished from non-problem alcohol use, then
marijuana use preceded problem drinking in the sequence of
progression. These sequences have also been observed in the small
number of prospective studies which have followed a cohort of
adolescents into early adulthood and examined the patterns of
progression in drug use (e.g. Kaplan et al, 1982; Yamaguchi and
Kandel, 1984a, b). For the majority (87 per cent) of men "the pattern
of progression is one in which the use of alcohol precedes marijuana;
alcohol and marijuana precede other illicit drugs; and alcohol,
cigarettes and marijuana precede the use of prescribed psychoactive
drugs" (Yamaguchi and Kandel, 1984a, p671). Among the majority of
women (86 per cent) the sequence was such that "either alcohol or
cigarettes precedes marijuana; alcohol, cigarettes and marijuana
precede other illicit drugs; alcohol and either cigarettes or
marijuana precede prescribed psychoactive drugs" (Yamaguchi and
Kandel, 1984a, p671).

Yamaguchi and Kandel (1984b) also examined variables which predicted
progression to illicit drug use beyond cannabis use. They were
specifically interested in "whether the use of certain drugs lower in
the sequence influences the initiation of higher drugs" (p673) and
used sophisticated statistical methods to discover if the statistical
relationship between cannabis use and subsequent illicit drug use
persisted after controlling for temporally prior variables, such as
pre-existing adolescent behaviours and attitudes, interpersonal
factors, and age of initiation into drug use. If the relationship
persisted after controlling for these variables, confidence was
increased that the relationship was a causal one.

Yamaguchi and Kandel found that the relationship between marijuana use
and progression to the use of other illicit drugs was not only
explained by friends' marijuana use (which also predicted
progression). Among men, the age of initiation of marijuana was an
important modifier of this relationship: men who initiated marijuana
use under the age of 16, were "even more likely to initiate other
illicit drugs than is expected from the longer period of risk
resulting from an early age of onset" (p677). Most importantly,
"persons who have not used marijuana have very small probabilities of
initiating other drugs, ranging from 0.01 to 0.03 (men) or 0.02
(women)" indicating that in their cohort, "marijuana appears to be a
necessary condition for the initiation of other illicit drugs" (p677).

The work of Kandel and her colleagues and that of other researchers
(e.g. O'Donnell and Clayton, 1982) has been interpreted by some as
confirming the "gateway drug" hypothesis or "the stepping stone theory
of drug use" (DuPont, 1984). Although it is not always clear what is
being claimed by proponents of this hypothesis, it does not imply that
a high proportion of those who experiment with marijuana will go on to
use heroin. Indeed, the overwhelming majority of cannabis users do not
use harder drugs like heroin. Kandel has explicitly disavowed this
interpretation of her work:

The notion of stages in drug behavior does not imply that these stages
are either obligatory or universal ... the model is not meant to be a
variant of the controversial `stepping-stone' theory of drug addiction
in which use of marijuana was assumed inexorably to lead to the use of
other illicit 'hard' drugs, especially heroin (Kandel, 1988, pp58-61).


The view that cannabis use generally leads to the use of other illicit
drugs is contradicted by the evidence from the studies of Kandel and
her colleagues. Cannabis use is largely a behaviour of late
adolescence and early adulthood. Kandel's research has shown that it
has been initiated by the age of 19 in 90 per cent of those who ever
used cannabis, and initiation is rare after 20 years. The frequency of
its use peaks in the early 20s, when 50 per cent of males and 33 per
cent of females reported using, and rapidly declines by age 23, with
"the assumption of the roles of adulthood .. getting married, entering
the labor force, or becoming a parent .. that may be incompatible with
involvement in illicit drugs and deviant lifestyles" (Kandel and
Logan, 1984, p665). Hence, although those who use cannabis are more
likely to use other illicit drugs than those who do not, it is more
usual for cannabis use to decline in early adult life, with only a
minority continuing to use regularly, or progressing to the use of
more dangerous illicit drugs. Even in the case of the minority (about
one in four) who progress to daily cannabis use, the majority cease
their use by the mid to late 20s (Kandel and Davies, 1992).

A better supported hypothesis is that cannabis use, especially heavy
cannabis use, greatly increases the chances of progressing to the use
of other illicit drugs. But even this type of relationship does not
necessarily mean that cannabis use "causes" heroin use. As Kandel
(1988) has stressed, the existence of sequential stages of progression
does not "necessarily imply causal linkages among different drugs".
The sequences "could simply reflect the association of each class of
drugs with different ages of initiation or [with pre-existing]
individual attributes, rather than the specific effects of the use of
one class of drug on the use of another" (Kandel, 1988, p61).

A plausible alternative hypothesis is that of selective recruitment.
That is, there is a selective recruitment to cannabis use of deviant
and nonconformist persons with a predilection for the use of
intoxicating substances. On this hypothesis, the sequence in which
drugs are typically used reflects their differential availability and
societal disapproval (e.g. Donovan and Jessor, 1983). Further, the
sequence of initiation into drug use is held to be a consequence of
the availability of different drugs at different ages, with the use of
the least available, and most strongly socially disapproved "hard"
drugs being last. This hypothesis exculpates cannabis use as a cause
of progression to other illicit drug use, since cannabis use and other
illicit drug use are the common consequences of adolescent deviance
and nonconformity (Kaplan et al, 1982; Newcombe and Bentler, 1988).

The selective recruitment hypothesis has received support from a
number of studies. There are substantial correlations between various
forms of nonconforming adolescent behaviour, such as, high school
drop-out, early premarital sexual experience and pregnancy,
delinquency, and alcohol and illicit drug use (Jessor and Jessor,
1977; Osgood et al, 1988). All such behaviours are correlated with
nonconformist and rebellious attitudes and anti-social conduct in
childhood (Shedler and Block, 1990) and early adolescence (Jessor and
Jessor, 1977; Newcombe and Bentler, 1988). Recent research indicates
that those who are most likely to use other illicit drugs, namely,
those who become regular cannabis users (Kandel and Davies, 1992), are
more likely to have a history of anti-social behaviour (Brook et al,
1992; McGee and Feehan, 1993), nonconformity and alienation (Brook et
al, 1992; Jessor and Jessor, 1978; Shedler and Block, 1990), perform
more poorly at school (Bailey et al, 1992; Hawkins et al, 1992; Kandel
and Davies, 1992), and use drugs to deal with personal distress and
negative affect (Kaplan and Johnson, 1992; Shedler and Block, 1990).
In general, the more of these risk factors that adolescents have, the
more likely they are to progress to more intensive involvement with
cannabis, and hence, to use other illicit drugs (Brook et al, 1992;
Newcombe, 1992; Scheier and Newcombe, 1991).

One way of testing the selective recruitment hypothesis is to discover
whether cannabis use continues to predict progression to "harder"
illicit drugs after statistically controlling for pre-existing
differences in personality and other characteristics (e.g. deviance)
between cannabis users and non-users. In several such studies (e.g.
Kandel et al, 1986; O'Donnell and Clayton, 1982; Robins et al, 1970)
the relationship between cannabis and heroin use has been reduced when
pre-existing differences have been controlled for, but in all cases
the relationship has persisted, albeit in attenuated form. O'Donnell
and Clayton (1982) have interpreted this type of finding as strong
evidence in favour of a causal connection between cannabis and heroin
use.

The credibility of such an argument for a causal interpretation of the
relationship between cannabis and heroin use depends upon whether the
most important prior characteristics have been adequately measured and
statistically controlled for in these studies. It would be difficult
to argue that this has been the case. Kandel et al (1986), for
example, were unable to measure the users' attitudes and family
characteristics at the time of drug initiation, or differential drug
availability, either or both of which "may account for the observed
relationships between the early and late stage drugs" (p679). In both
the studies of O'Donnell and Clayton (1982) and Robins et al (1970)
the measures of deviance "prior" to drug use were assessed
retrospectively with unknown validity. Baumrind (1983) has contested
the ability of these studies to exclude the alternative hypothesis
that personality differences which preceded cannabis use were the
causes of the progression to heroin use. She has argued that "it is
safer in the absence of evidence of external validity" of these
measures to assume that the relationship between marijuana use and
heroin use is spurious.

Even if we assume for the purpose of argument that the association
between cannabis and heroin use is not wholly explained by
pre-existing differences in deviant behaviour between cannabis users
and non-users, it remains to be explained how cannabis use "causes"
heroin use. It may seem superficially plausible to suggest that there
is something about the pharmacological effect of cannabis which
predisposes heavy users to progress to the use of other intoxicants,
but there is no obvious pharmacological mechanism for such
progression. Is it the development of tolerance to the positive
effects of cannabis, or to some form of experiential satiation with
its effects? Does the euphoria of cannabis awaken appetite for
intoxication by other drugs? These possibilities are difficult to
test.

Any pharmacological explanation in which more potent illicit drugs
serve as "substitutes" for less potent drugs like alcohol and cannabis
has to contend with a number of facts. As already indicated, there are
relatively low rates of progression from cannabis use to the sustained
use of other illicit drugs; experimentation and abandonment is more
the norm. Even those heavy cannabis users who use other illicit drugs
continue to use cannabis as well as the new illicit drugs. As Donovan
and Jessor (1983) have noted: "...`harder' drugs do not serve as
substitutes for `softer' drugs. Rather, a deepening of regular
substance use appears to go along with a widening of experience in the
drug domain" (p548-549).

There is also good reason for believing that the pattern of
progression observed among American adolescents in the 1970s was
conditioned by historical differences in drug availability (Kandel,
1978). Historical evidence from among earlier cohorts of heroin users
indicated that prior involvement with cannabis was confined to those
geographic areas of the US in which it was readily available (Goode,
1974). Research on African-American adolescents also showed a
variation in the sequence of drug use, with the use of more readily
available cocaine and heroin preceding the use of the less readily
available hallucinogens and "pills" (Kandel, 1978). Most dramatically,
American soldiers in Vietnam were more likely to use heroin than
alcohol because heroin was cheaper and more freely available than
alcohol to most American troops who were younger than the minimum
drinking age of 21 (Robins, 1993).

The historical and geographical variations in sequencing of illicit
drug use suggest a sociological explanation of both the sequencing of
illicit drug use and the higher rates of progression to heroin use
among heavy cannabis users. One of the most popular sociological
hypotheses is that cannabis use increases the chance of using other
illicit drugs by increasing contact with other drug users as part of a
drug using subculture. On this hypothesis, heavy cannabis use leads to
greater involvement in a drug using subculture which, in turn, exposes
cannabis users to the example of peers who have used other illicit
drugs. Such exposure also increases opportunities to use other illicit
drugs because of their increased availability within their social
circle, and places the individual in a social context in which illicit
drug use is encouraged and approved (e.g. Goode, 1974).

Although plausible, there is surprisingly little direct evidence on
the drug subculture hypothesis. Goode (1974) presented data from the
late 1960s indicating that the number of friends who used heroin was a
stronger predictor of heroin use than was frequency of cannabis use,
arguing that the "correlation between frequency of use and the use of
dangerous drugs ... [is] the result of interaction and involvement
with others who use" (p332). These observations have been supported by
Kandel's (1984) finding that the strongest predictor of continued
cannabis use in early adulthood was the number of friends who were
cannabis users.

The hypotheses of selective recruitment and socialisation in a
drug-using subculture are not mutually exclusive; both processes could
independently contribute to the relationship between regular marijuana
use and progression to heroin use (Goode, 1974). As already noted, the
selective recruitment hypothesis is supported by the consistent
finding of pre-existing differences between those who use marijuana
and those who do not, which are most marked in those whose continued
use of cannabis predicts their use of other illicit drugs. Once
initiated into cannabis use, heavy users become further distinguished
from non-users and those who have discontinued their use by the
intensity of their social relations and activities which involve the
use of marijuana, such as mixing with other drug users, and buying and
selling illicit drugs. The illegality of these activities confers on
the use, possession and sale of cannabis a socialising and subcultural
influence not possessed by the possession and use of the legal drugs
(Goode, 1974).

On the available evidence, the case for a pharmacological explanation
of the role of cannabis use in progression to other illicit drug use
is weak. A sociological explanation is more plausible than a
pharmacological one. The predictive value of cannabis use is more
likely to reflect a combination of: the selective recruitment to heavy
cannabis use of persons with combination of pre-existing personality
and attitudinal traits that predispose to the use of other
intoxicants; and the effects of socialisation into an illicit drug
subculture in which there is an increased availability of, and
encouragement to use, other illicit drugs.



7.1.2 Educational performance

A major concern about the effects of adolescent cannabis use has been
the possibility that its use impairs educational performance, and
increases the chances of students discontinuing their education. Such
a possibility is plausible: heavy cannabis use in the high school
years would impair memory and attention, thereby interfering with
learning in and out of the classroom (Baumrind and Moselle, 1985). If
use became chronic, persistently impaired learning would produce
poorer performance in high school and later in college, and increase
the chance of a student dropping out of school. If the adolescent's
school performance was marginal to begin with, as research reviewed
above suggests it is more likely to be among marijuana users, then
regular use could increase the pre-existing risk of high school
failure. Because of the importance of high school education to
occupational choice, this potential effect of adolescent cannabis use
could have consequences which ramified throughout the affected
individual's adult life.

Such a possibility has been supported by cross-sectional studies (e.g.
Kandel, 1984; Robins et al, 1970). These and other studies (see
Hawkins et al, 1992) have found a positive relationship between degree
of involvement with cannabis as an adult and the risk of dropping out
of high school. Studies of relationships between performance in
college and marijuana smoking have produced more equivocal results
(see below), usually failing to find consistent evidence that the
performance of cannabis users was more impaired than would be
predicted by their performance prior to cannabis use. These studies
have been criticised (Baumrind and Moselle, 1985; Cohen, 1982),
however. Baumrind and Moselle have argued that grade point average is
an insensitive measure of adverse educational effects among bright
high school and college students, while Cohen has argued that students
whose learning has been most adversely affected by their chronic heavy
cannabis use would not be found in college samples (Cohen, 1982).

Longitudinal studies of the effect of cannabis use on educational
achievement have produced mixed support for the hypothesis (e.g.
Kandel et al, 1986; Newcombe and Bentler, 1988). Kandel et al (1986),
for example, analysed the follow-up data from the cohort on which
their earlier cross-sectional finding of a relationship between
cannabis use and high school drop-out had been reported. They reported
a negative relationship between marijuana use in adolescence and years
of education completed in early adulthood but this relationship
disappeared once account was taken of the fact that those who used
cannabis in adolescence had much lower educational aspirations than
those who did not.

Newcombe and Bentler (1988) used a different approach to analysis in
their study of the effects of adolescent drug use on educational
pursuits in early adulthood. They used a composite measure of degree
of drug involvement, which measured frequency of use of alcohol,
cannabis and "hard drugs", and a measure of social conformity in
adolescence as a control variable in the analyses, which examined the
relationships between adolescent drug use and educational pursuits in
early adulthood. They found negative correlations between adolescent
drug use and high school completion, but after controlling for the
higher nonconformity and lower academic potential among adolescent
drug users, there was only a modest negative relationship between drug
use and college involvement. The only specific effect of any
particular type of drug use, over and above their measure of drug use
involvement, was a negative relationship between hard drug use in
adolescence and high school completion.

On the whole then, the available evidence from the longitudinal
studies suggests that there may be a modest statistical relationship
between cannabis and other illicit drug use in adolescence and poor
educational performance. The apparently strong relationship between
cannabis use and high school drop-out observed in cross-sectional
studies exaggerates the adverse impact of cannabis use on school
performance because adolescents who perform less well at school, and
have lower academic aspirations, are more likely to use cannabis. But
even if the relationship is statistically small, it may be
substantively important, especially among those whose educational
performance was marginal to begin with, because of the adverse effects
that educational underachievement has on subsequent life choices, such
as occupation, and the opportunities that they provide or exclude.



7.1.3 Occupational performance

Among those young adult cannabis users who enter the work-force, the
continued use of cannabis and other illicit drugs in young adulthood
might impair job performance for the same reasons that it has been
suspected of impairing school performance, namely, that chronic
intoxication impairs work performance. There is some suggestive
support for this expectation, in that cannabis users report higher
rates of unemployment than non-users (e.g. Kandel, 1984; Robins et al,
1970), but this comparison is likely to be confounded by the different
educational qualifications of the two groups. Longitudinal studies
have suggested that there is a relationship between adolescent
marijuana use and job instability among young adults which is not
explained by differences in education and other characteristics which
precede cannabis use (e.g. Kandel et al, 1986). Newcombe and Bentler
(1988) provided a more extensive analysis of the effects of adolescent
drug use on occupational performance in young adulthood. They examined
the relationships between adolescent drug use and income, job
instability, job satisfaction, and resort to public assistance in
young adulthood, while controlling for differences between users and
non-users in social conformity, academic potential and income in
adolescence. Their findings supported those of Kandel and colleagues
in that adolescent drug users had a larger number of changes of job
than non-drug users. Newcombe and Bentler conjectured that this
reflects either impaired work performance, or a failure of illicit
drug users to develop responsible employment behaviours such as
conscientiousness, thoroughness, and reliability.



7.1.4 Interpersonal relationships

There are developmental and empirical reasons for suspecting that
cannabis use may adversely affect interpersonal relationships. The
developmental reason is that heavy adolescent drug use may produce a
developmental lag, entrenching adolescent styles of thinking and
coping which would impair the ability to form adult interpersonal
relationships (Baumrind and Moselle, 1985). The empirical reason is
the strong positive correlation between drug use, precocious sexual
activity, and early marriage, which in turn predicts a high rate of
relationship failure (Newcombe and Bentler, 1988).

Cross-sectional studies of drug use in young adults have indicated
that a high degree of involvement with marijuana predicts a reduced
probability of marriage, an increased rate of cohabiting, an increased
risk of divorce or terminated de facto relationships, and a higher
rate of unplanned parenthood and pregnancy termination (Kandel, 1984;
Robins et al, 1970). Kandel (1984) also found that heavy cannabis
users were more likely to have a social network in which friends and
the spouse or partner were also cannabis users (Kandel, 1984). These
findings have been largely confirmed in analyses of the longitudinal
data from this cohort of young adults (Kandel et al, 1986).

Newcombe and Bentler (1988) found similar relationships between drug
use and early marriage in their analysis of the cross-sectional data
from their cohort of young adults in Los Angeles. Drug use in
adolescence predicted an increased rate of early family formation in
late adolescence and of divorce in early adulthood, which they
interpreted as evidence that: "early drug involvement leads to early
marriage and having children which then results in divorce" (p97).
Newcombe and Bentler argued that this finding provided evidence for
their theory of "precocious development", according to which drug use
accelerates development and "... drug users tend to bypass or
circumvent the typical maturational sequence of school, work and
marriage and become engaged in adult roles of jobs and family
prematurely without the necessary growth and development to enhance
success with these roles ... [developing] a pseudomaturity that ill
prepares them for the real difficulties of adult life" (pp35-36).

Less attention has been paid to the possibility that cannabis use has
adverse effects on the development of social relationships outside
marriage. Newcombe and Bentler (1988) have reported one of the few
such studies. They investigated the relationship between adolescent
drug use and degree of social support and the experience of loneliness
reported in young adulthood. Cross-sectional analyses of data on drug
use and degree of social support in adolescence showed that drug users
reported having less social support than non-users (Newcombe and
Bentler, 1988). But the effects of adolescent drug use on social
support and loneliness in young adulthood were minor. Alcohol use in
adolescence was associated with decreased loneliness in adulthood,
while only hard drug use in adolescence was associated with decreased
social support and increased loneliness in early adulthood.



7.1.5 Mental health

The impact of adolescent cannabis and other drug use on general health
in early adult life has not been investigated, in large part because
it will be difficult to detect any adverse effects of adolescent drug
use on adult health in the longitudinal studies that have been
conducted. In such cohorts, heavy cannabis use - the riskiest pattern
of use from the perspective of health effects - has generally been
observed to occur at low rates. In any case, young adulthood is too
soon to expect any adverse health effects to be evident, because of
the relatively short period of use by young adults.

For good reasons, the effects of cannabis use on mental health have
been the health outcomes most studied. Cannabis is a psychoactive drug
which effects the users' mood and feeling, so chronic heavy use could
possibly adversely affect mental health, especially among those whose
adjustment prior to their cannabis use was poor and who use cannabis
to modulate and control their negative mood states and emotions. The
relationships between cannabis use and the risks of developing
dependence upon cannabis or major mental illnesses such as
schizophrenia, are reviewed below (see pp110-122 and pp173-178
respectively). In this section attention is confined to non-psychotic
symptoms of depression and distress.

A number of studies have suggested an association between cannabis use
and poor mental health. Kandel's (1984) cross-sectional study found an
inverse association between the intensity of marijuana involvement and
degree of satisfaction with life, and a positive association between
marijuana involvement and a greater likelihood of having consulted a
mental health professional, and having been hospitalised for a
psychiatric disorder (Kandel, 1984). Longitudinal analyses of this
same cohort, however, found only weak associations between adolescent
drug use and these adult outcomes; the strongest relationship between
adolescent drug use and mental health, was a positive relationship
between cigarette smoking in adolescence and increased symptoms of
depression in adulthood (Kandel et al, 1986).

The cross sectional adult data in Newcombe and Bentler's (1988) study
showed strong relationships between adolescent drug use and emotional
distress, psychoticism and lack of a purpose in life. Emotional
distress in adolescence predicted emotional distress in young
adulthood, but there were no relationships between adolescent drug use
and the experience of emotional distress, depression and lack of a
sense of purpose in life in young adulthood. There were a number of
small but substantively significant effects of adolescent drug use on
mental health in young adulthood. Adolescent drug use predicted
psychotic symptoms in young adulthood, and hard drug use in
adolescence predicted increased suicidal ideation in young adulthood,
after controlling for general drug use and earlier emotional distress.
Newcombe and Bentler interpreted these findings as evidence that
adolescent drug use "interferes with organised cognitive functioning
and increases thought disorganisation into young adulthood" (p180).



7.1.6 Delinquency and crime

Since initiation into illicit drug use and the maintenance of regular
illicit drug use are both strongly related to degree of social
nonconformity or deviance (e.g. Donovan and Jessor, 1980; Newcombe and
Bentler, 1988; Polich et al, 1984) it is reasonable to expect
adolescent illicit drug use to predict social nonconformity and
various forms of delinquency and crime in young adulthood.
Cross-sectional studies of adult drug users seem to support this
hypothesis: they indicate that there is a relationship between the
extent of marijuana use as an adult and a history of lifetime
delinquency (e.g. Kandel, 1984; Robins et al, 1970), having been
convicted of an offence, and having had a motor vehicle accident while
intoxicated (Kandel, 1984).

Johnston et al (1978) reported a detailed analysis of the relationship
between intensity of drug use and delinquency across two waves of
interviews of adolescent males undertaken as part of the "Youth in
Transition" study. They found in their cross-sectional data that there
was a strong relationship between involvement in delinquency and
degree of involvement with illicit drugs, that is, self-reported rates
of delinquent activity increased steadily with increasing degree of
drug involvement. However, a series of analyses looking at changes in
drug use and crime over time indicated that the groups defined on
intensity of drug involvement differed strongly in their rate of
delinquent acts before their drug use. Moreover, the onset of illicit
drug use (including cannabis) had little effect on delinquent acts,
except perhaps among those who used heroin, among whom there was a
suggestion that the rates of delinquency increased. Finally, rates of
delinquent acts declined over time in all drug use groups and at about
the same rate. The findings were interpreted as delivering "a
substantial, if not mortal, blow" to the hypothesis that "drug use
somehow causes other kinds of delinquency" (p156).

Newcombe and Bentler (1988) reported a somewhat more complicated
although no less plausible picture in their longitudinal study. They
reported a positive relationship between drug use and criminal
involvement in adolescence, but found more mixed results in the
relationship between adolescent drug use and criminal activity in
young adulthood. Adolescent drug use predicted drug crime involvement
in young adulthood; but after controlling for other variables, it was
negatively correlated with violent crime, and general criminal
activities in young adulthood. Newcombe and Bentler argued that these
negative correlations indicated that the correlation between different
forms of delinquency in adolescence decreases with age, as criminal
activities become differentiated into drug-related and
non-drug-related offences. Hard drug use in adolescence also had a
specific effect on young adult crime over and above that of drug use
in general: it predicted an increased rate of criminal assaults in
young adulthood.



7.1.7 Conclusions

There are a number of clear outcomes of research on adolescent
cannabis and other illicit drug use. First, there is strong continuity
of development from adolescence into early adult life in which many of
the indicators of adverse development which have been attributed to
cannabis use precede its first use (Kandel, 1978). These include minor
delinquency, poor educational performance, nonconformity, and poor
adjustment. Second, there was a predictable sequence of initiation
into the use of illicit drugs among American adolescents in the 1970s
in which the use of licit drugs preceded experimentation with
cannabis, which preceded the use of hallucinogens and "pills", which
in turn preceded the use of heroin and cocaine. Generally, the earlier
the age of initiation into drug use, and the greater the involvement
with any drug in the sequence, the greater the likelihood of
progression to the next drug in sequence.

The causal significance of these findings, and especially the role of
cannabis in the sequence of illicit drug use, remains controversial.
The hypothesis that the sequence of use represents a direct
pharmacological effect of cannabis use upon the use of later drugs in
the sequence is the least compelling. A more plausible and better
supported explanation is that it reflects a combination of the
selective recruitment into cannabis use of nonconforming and deviant
adolescents who have a propensity to use illicit drugs, and the
socialisation of cannabis users within an illicit drug using
subculture which increases the exposure, opportunity, and
encouragement to use other illicit drugs.

There has been some support for the hypothesis that heavy adolescent
use of cannabis impairs educational performance. Cannabis use appears
to increase the risk of failing to complete a high school education,
and of job instability in young adulthood. The apparent strength of
these relationships in cross-sectional studies has been exaggerated
because those who are most likely to use cannabis have lower
pre-existing academic aspirations and high school performance than
those who do not. Even though more modest than has sometimes been
supposed, the apparently adverse effects of cannabis and other drug
use upon educational performance may cascade throughout young adult
life, affecting choice of occupation, level of income, choice of mate,
and quality of life of the user and his or her children.

There is weaker but suggestive evidence that heavy cannabis use has
adverse effects upon family formation, mental health, and involvement
in drug-related (but not other types of) crime. In the case of each of
these outcomes, the apparently strong associations revealed in
cross-sectional data are much more modest in longitudinal studies
after statistically controlling for associations between cannabis use
and other variables which predict these adverse outcomes.

On balance, there are sufficient indications that cannabis use in
adolescence adversely affects adolescent development to conclude that
it is a socially desirable goal to discourage adolescent cannabis use,
and especially regular cannabis use.



7.2 Psychological adjustment in adults



7.2.1 Is there an amotivational syndrome?

Anecdotal reports that chronic heavy cannabis use impairs motivation
and social performance have been described in the older literature on
cannabis use in societies with a long history of use, such as Egypt,
the Carribean and elsewhere (e.g. Brill and Nahas, 1984). In these
societies, heavy cannabis use is the prerogative of the poor,
impoverished and unemployed. With the increase of cannabis use among
young adults in the USA in the early 1970s, there were clinical
reports of a similar syndrome occurring among heavy cannabis users
(e.g. Kolansky and Moore, 1971; Millman and Sbriglio, 1986; Tennant
and Groesbeck, 1972). These investigators have typically described a
state among chronic, heavy cannabis users in which the users' focus of
interest narrowed, they became apathetic, withdrawn, lethargic,
unmotivated, and showed evidence of impaired memory, concentration and
judgment (Brill and Nahas, 1984; McGlothin and West, 1968). This
constellation of symptoms has been described as an "amotivational
syndrome" (e.g. McGlothin and West, 1968; Smith, 1968), which some
have claimed is an organic brain syndrome caused by the effects of
chronic cannabis intoxication (Tennant and Groesbeck, 1972). All these
reports have been uncontrolled, and often poorly documented, so that
it has not been possible to disentangle the effects of chronic
cannabis use from those of poverty and low socioeconomic status, or
pre-existing personality and other psychiatric disorders (Edwards,
1976; Millman and Sbriglio, 1986; National Academy of Science, 1982;
Negrete, 1983).

There is no research evidence which unequivocally demonstrates that
cannabis does or does not adversely affect the motivation of chronic
heavy adult cannabis users. It has proved singularly difficult to
provide better controlled research evidence which has permitted a
consensus to emerge upon the issue. Two types of investigation have
been carried out in an attempt to assess the motivational effects of
chronic heavy cannabis use: field studies of chronic heavy cannabis
using adults in societies with a tradition of such use, e.g. Costa
Rica (Carter et al, 1980) and Jamaica (Rubin and Comitas, 1975); and
laboratory studies of the effects on the motivation and performance of
volunteers who have been administered heavy doses of cannabis over
periods of up to 21 days (e.g. Mendelson et al, 1974). There has also
been some evidence on the prevalence of adverse psychological effects
of cannabis from a small number of studies of chronic cannabis users
(e.g. Halikas et al, 1982).



7.2.2 Field studies of motivation and performance

Rubin and Comitas (1975) examined the effects of ganja smoking on the
performance of Jamaican farmers who regularly smoked cannabis in the
belief that it enhanced their physical energy and work productivity.
They used videotapes to measure movement and biochemical measures of
exhaled breath to assess caloric expenditure before and after ganja
smoking. Four case histories were reported which indicated that the
level of physical activity increased immediately after smoking ganja,
as did caloric expenditure, but not productivity. It seemed to be that
after smoking ganja the workers engaged in more intense and
concentrated labour, but this was done less efficiently, especially by
heavy users. Contrary to the hypothesis that cannabis use produced an
impairment in motivation, they concluded: "In all Jamaican settings
observed, the workers are motivated to carry out difficult tasks with
no decrease in heavy physical exertion, and their [mistaken]
perception of increased output is a significant factor in bolstering
their motivation to work." (p79).

A study of Costa Rican cannabis smokers produced mixed evidence on the
impact of chronic cannabis use on job performance (Carter et al,
1980). A comparison was made of the employment histories of 41 pairs
of heavy users (10 marijuana cigarettes per day for 10 or more years)
and non-users who had been matched on age, marital status, education,
occupation, and alcohol and tobacco consumption. The comparison
indicated that non-users were more likely than users to have attained
a stable employment history, to have received promotions and raises,
and to be in full-time employment. Users were also more likely to
spend all or more than their incomes, and to be in debt. Among users,
however, the relationship between average daily marijuana consumption
and employment was the obverse of what the amotivational hypothesis
would predict, that is, those "who had steady jobs or who were
self-employed were smoking more than twice as many marijuana
cigarettes per day as those with more frequent job changes, or those
who were chronically unemployed" (p153), indicating that "the level of
consumption was related more to relative access than to individual
preference" (p154).

Evidence from these field studies is usually interpreted as failing to
demonstrate the existence of the amotivational syndrome (e.g.
Dornbush, 1974; Hollister, 1986; Negrete, 1988). There are critics,
however, who raise doubts about how convincing such apparently
negative evidence is. Cohen (1982), for example, has argued that the
chronic users in three field studies have come from socially marginal
groups, so that the cognitive and motivational demands of their
everyday lives were insufficient to detect any impairment caused by
chronic cannabis use. Moreover, the sample sizes of these studies have
been too small to exclude the possibility of an effect occurring among
a minority of heavy users.

Other evidence suggests that an amotivational syndrome is likely to be
a rare occurrence, if it exists. Halikas et al (1982), for example,
followed up 100 regular cannabis users six to eight years after
initially recruiting them and asked them about the experience of
symptoms suggestive of an amotivational syndrome. They found only
three individuals who had ever experienced such a cluster of symptoms
in the absence of significant symptoms of depression. These
individuals were not distinguished from the other smokers by their
heaviness of use. Nor was their experience of these symptoms obviously
related to changes in pattern of use; they seemed to come and go
independently of continued heavy cannabis use.



7.2.3 Laboratory studies of motivation and performance

In the light of Halikas et al's low estimate of the prevalence of
amotivational symptoms among chronic heavy cannabis users, it is
perhaps not surprising that the small number of laboratory studies of
long-term heavy cannabis use have failed to provide unequivocal
evidence of impaired motivation (Edwards, 1976). The early studies
conducted as part of the LaGuardia Commission inquiry (see Mendelson
et al, 1974) reported deterioration in behaviour among prisoners given
daily doses of cannabis over a period of some weeks, but these reports
were based upon largely uncontrolled observation. So too was the more
recent study of Georgotas and Zeidenberg (1979) in which it was
reported that five healthy male marijuana users who were placed on a
dose regimen of 210mg of THC per day for a month appeared "moderately
depressed, apathetic, at times dull and alienated from their
environment and with impaired concentration" (p430).

A study which used standardised measures of performance rather than
relying on observational data failed to observe such effects
(Mendelson et al, 1974). In this study 10 casual and 10 heavy cannabis
smokers were observed over a 31 days study period in a research
laboratory. For 21 of these days, subjects were given access to as
many marijuana cigarettes as they earned by performing a simple
operant task which involved pressing a button to move a counter. The
points could be exchanged for money (60 points equal to a cent),
packets of cigarettes (3,000 each), and marijuana cigarettes (6,000
each). Mendelson et al found that all subjects earned the maximum
number of points allowed per day (60,000) throughout the study and
that output was unaffected by marijuana smoking whereas ad libitum
access to alcohol by heavy drinking subjects in the same setting
profoundly disrupted performance of the same task. Mendelson et al
concluded that: "our data disclosed no indication of a relationship
between decrease in motivation to work at an operant task and acute or
repeat dose effects of marihuana" (p176).

A number of criticisms can be made of this study. First, the period of
heavy use was only 21 days by comparison with the life histories of 15
or more years daily use in heavy cannabis users in the field studies.
Second, the subjects in the study were volunteers who were all
healthy, young cannabis users with a mean IQ of 120 and nearly three
years of college education, and some of whom reported during
debriefing that they were motivated to perform well so as to
demonstrate that their cannabis use did not have any adverse effect on
their performance (Mendelson et al, 1974). Third, the tasks that users
were asked to perform (button presses) were undemanding. Mendelson et
al countered that these tasks had nonetheless been shown to detect the
deleterious effects of heavy alcohol use. Moreover, they argued, there
were other indicators that their subjects' performance and motivation
was unimpaired while using cannabis, namely, all subjects completed
the study, most undertook the daily assessments conducted throughout,
all complied with a roster for cleaning and house-keeping duties, and
all kept up their preferred recreational activities throughout the
study period.

A similar study was completed at the Addiction Research Foundation,
the results of which have not been fully published, although Campbell
(1976) has provided a brief account of its findings. In this study,
young cannabis users were studied in a residential token economy in
which they could earn tokens that could be exchanged for money and
other goods by manufacturing woven woollen belts. Unlike the Mendelson
study, subjects' cannabis doses were under the experimenters' control
and subjects were given mandatory high doses. The subjects showed no
gross behavioural changes, no social deterioration, and no alterations
in intellectual functioning, but the results suggested, contrary to
those of Mendleson et al, that chronic heavy cannabis use reduced
productivity, especially during the period of mandatory high dosing
(30mg of THC per day) which many subjects found aversive. It remains
unclear how applicable the results of performance with mandatory high
dosing are to the situation where users have control over their own
dose.



7.2.4 Discussion

The status of the amotivational syndrome remains contentious, in part
because of differences in the appraisal of evidence from clinical
observations and controlled studies. On the one hand, there are those
who find the small number of cases of "amotivational syndrome"
compelling clinical evidence of the marked deterioration in
functioning that chronic heavy cannabis use can produce. On the other,
there are those who are more impressed by the largely unsupportive
findings of the small number of field and laboratory studies. Although
the controlled studies have largely been interpreted as failing to
substantiate the clinical observations (e.g. Millman and Sbriglio,
1986), the possibility has been kept alive by suggestive reports that
regular cannabis users experience a loss of ambition and impaired
school and occupational performance as adverse effects of their use
(e.g. Hendin et al, 1987), and that some ex-cannabis users give
impaired occupational performance as a reason for stopping (Jones,
1984). It seems reasonable to conclude that if there is an
amotivational syndrome, it is a relatively rare consequence of
prolonged heavy cannabis use. If this is the case, then studies of
motivation and performance among dependent cannabis users may be the
most promising place to look for examples of the syndrome.

Even if we assume that chronic heavy cannabis use impairs adult
motivation and performance, there remains the question of mechanism
(Baumrind, 1983). Is there a specific amotivational syndrome caused by
the chronic intake of cannabinoids, or are we mistaking it for the
impaired cognitive and psychomotor performance of chronically
intoxicated dependent cannabis users (Edwards, 1976)? Are we perhaps
mistaking a depressive syndrome among heavy cannabis users for the
amotivational syndrome? (Cohen, 1982) Assuming that cases can be
identified, how easy is it to reverse the syndrome or behaviour
pattern after a period of abstinence from cannabis?



7.2.5 Conclusions

The evidence for an amotivational syndrome among adults is, at best,
equivocal. The positive evidence largely consists of case histories,
and observational reports. The small number of controlled field and
laboratory studies have not found compelling evidence for such a
syndrome, although their evidential value is limited by the small
sample sizes and limited sociodemographic characteristics of the field
studies, by the short periods of drug use, and the youthful good
health and minimal demands made of the volunteers observed in the
laboratory studies. It nonetheless is reasonable to conclude that if
there is such a syndrome, it is a relatively rare occurrence, even
among heavy, chronic cannabis users.



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7.3 Is there a cannabis dependence syndrome?



7.3.1 The significance of dependence

If there is a cannabis dependence syndrome, it has important
implications for both cannabis users and public health (Edwards,
1982). First, people who currently use cannabis, and young adults who
are considering whether to use it, should make decisions which are
informed by an appraisal of the risk of their becoming dependent on
the drug. If there is a risk of dependence, and cannabis continues to
be regarded as a drug that does not produce dependence, such decisions
cannot be informed.

Second, if there is a cannabis dependence syndrome, then persons who
become dependent on cannabis place themselves at an increased risk of
experiencing any adverse health effects attributable to cannabis use.
Dependent cannabis users typically smoke two or more cannabis
cigarettes daily over many years, putting themselves at risk of the
pulmonary hazards of smoking. A chronic state of cannabis intoxication
could place them at increased risk of accidents, and the THC they
absorb may accumulate in their bodies, placing them at increased risk
of experiencing any adverse health effects of THC (Edwards, 1982).

Third, although a dependent pattern of cannabis use may be rare in
comparison with the more prevalent pattern of experimental and
intermittent use, it may nonetheless have public health significance
because of the widespread experimentation with cannabis in many
Western societies. The public health significance of cannabis
dependence would also increase if the prevalence of use substantially
increased as a result of changes in the availability of the drug.



7.3.2 The nature of dependence

For much of the 1960s and 1970s the apparent absence of tolerance to
the effects of cannabis, and of a withdrawal syndrome analogous to
that seen in alcohol and opioid dependence, supported the consensus of
informed opinion that cannabis was not a drug of dependence. Expert
views on the nature of dependence changed during the late 1970s and
early 1980s, when the more liberal definition of drug dependence
embodied in Edwards and Gross's (1976) alcohol dependence syndrome was
extended to all psychoactive drugs (Edwards et al, 1981). The drug
dependence syndrome reduced the emphasis upon tolerance and
withdrawal, and attached greater importance to symptoms of a
compulsion to use, a narrowing of the drug using repertoire, rapid
reinstatement of dependence after abstinence, and the high salience of
drug use in the user's life. This new conception influenced the
development of the Third Revised Edition of the Diagnostic and
Statistical Manual of the American Psychiatric Association (1987)
(DSM-III-R), which reduced the importance of tolerance and withdrawal
symptoms in favour of a greater emphasis upon continued use of a drug
in the face of its adverse effects.



7.3.2.1 Drug dependence in DSM-III-R

"Psychoactive substance use disorders" include all forms of drug and
alcohol dependence in DSM-III-R (American Psychiatric Association,
1987; Kosten et al, 1987). "The essential feature of this disorder is
a cluster of cognitive, behavioral and physiologic symptoms that
indicate that the person has impaired control of psychoactive
substance use and continues use of the substance despite adverse
consequences" (p166). A diagnosis of psychoactive substance dependence
is made if any three of the nine criteria listed below have been
present for one month or longer:

1.  the substance is often taken in larger amounts or over a longer
period than the person intended;

2.  there is a persistent desire or one or more unsuccessful efforts
to cut down or control substance use;

3. a great deal of time is spent in activities necessary to get the
substance (e.g., theft), taking the substance..., or recovering from
its effects;

4.  frequent intoxication or withdrawal symptoms when expected to
fulfil major role obligations at work, school, or home..., or when
substance use is physically hazardous...;

5.  important social, occupational, or recreational activities given
up or reduced because of substance use;

6. continued substance use despite knowledge of having a persistent or
recurrent social, psychological, or physical problem that is caused or
exacerbated by the use of the substance;

7. marked tolerance;

8. characteristic withdrawal symptoms;

9. substance often taken to relieve or avoid withdrawal symptoms"
(American Psychiatric Association, 1987, pp167-8).

Criteria 8 and 9, are not required for the dependence syndromes of
cannabis, hallucinogens and PCP to be diagnosed.

These criteria may seem to conflict with community conceptions of drug
dependence, in that they explicitly include tobacco smoking as a form
of drug dependence, and could conceivably include caffeine dependence
(among heavy coffee drinkers). The fact that these forms of drug
taking are not usually be regarded as producing drug dependence is
less a reason for rejecting these diagnostic criteria than a signal of
the need to persuade the community to adopt a broader conception of
drug dependence, which reduces the emphasis upon "physical" dependence
as evidenced by the occurrence of a marked withdrawal syndrome on
abstinence.



7.3.2.2 Cannabis tolerance and withdrawal: experimental evidence

Although tolerance and withdrawal symptoms are not required within
DSM-III-R, there is evidence that both can occur under certain
conditions of dosing with cannabinoids. This should not be surprising
since, as Hollister (1986) has observed, cannabis "would have been an
exceptional centrally acting drug if tolerance/dependence were not one
of its properties" (p9). Yet for many years it was believed that there
was little tolerance to cannabis and no withdrawal syndrome. The
predominant recreational pattern of intermittent use in the community,
and the use of low doses of THC and short dosage schedules in
laboratory studies, contributed to this belief (Hollister, 1986), as
did the expectation that if there was a cannabis withdrawal syndrome,
it would be as readily recognised as the opioid withdrawal syndrome
(Edwards, 1982).

Since the middle 1970s evidence has emerged from human and animal
studies that chronic administration of high doses of THC results in
the development of marked tolerance to a wide variety of cannabinoid
effects, such as cardiovascular effects, and to the subjective high in
humans (Compton, Dewey, and Martin, 1990; Fehr and Kalant, 1983;
Hollister, 1986; Jones, Benowitz, and Herning, 1981; National Academy
of Science, 1982). Moreover, the abrupt cessation of chronic high
doses of THC generally produces a mild withdrawal syndrome like that
produced by other long-acting sedative drugs (Compton et al, 1990;
Jones and Benowitz, 1976; Jones et al, 1981).

Jones and Benowitz (1976) provided convincing evidence in humans of
the development of tolerance to the cardiovascular and subjective
effects of THC. They conducted human laboratory studies of the effects
of high doses of THC (210 mg per day) administered orally over a
period of 30 days on a fixed dosing schedule to healthy male
volunteers who had an extensive history of cannabis use. Clinical
observations of the subjects showed that as the duration of the high
dose regimen increased, there was a decline in the positive effects of
intoxication, and in the subjects' ratings of the "high". There was a
marked deterioration in the subjects' social functioning according to
nurses' ratings during the early days of the high dose regimen, but
there was almost complete recovery to baseline levels by the end of
the dosing period. There was similar evidence of recovery in cognitive
and psychomotor performance in the course of the high dose regimen.

The most convincing evidence of tolerance came from observations of
the cardiovascular and subjective effects of smoking a marijuana
cigarette at various points during the study. The magnitude of both
the cardiovascular and subjective responses to smoking a single
"joint" decreased with the length of time subjects had received a high
dose of THC. After a few days of high doses of THC, the increased
heart rate was replaced by a normal, and in some cases a slowed, heart
rate. Similarly, self-ratings indicated that the "high" produced by
the cigarette all but disappeared in the course of the high dose
regimen.

Similar observations of tolerance to the subjective effects of
cannabis have been made by Georgotas and Zeidenberg (1979). They
studied five healthy male marijuana smokers over a four-week period,
in which they smoked an average of 10 joints per day, providing an
average daily dose of 210mg of THC. In the course of this experiment,
subjects rapidly developed tolerance to the drug's effects:

Although initially they found the marijuana to be of good quality,
they now found it much weaker and inferior to what they were getting
outside. They felt it did not make them as high as often as they were
accustomed (p429).

An abstinence syndrome has been observed in monkeys maintained on a
schedule of chronic high doses of THC. Its symptoms consisted of:
"yawning, anorexia, piloerection, irritability, tremors and
photophobia" (Jones and Benowtiz, 1976). Similar symptoms were
observed by Jones and Benowitz (1976) after their subjects were
abruptly withdrawn from high doses of THC. Within six hours of
withdrawal subjects complained of "inner unrest", and by 12 hours,
"increased activity, irritability, insomnia, and restlessness were
reported by the subjects and obvious to staff" (p632). Common symptoms
reported were " `hot flashes', sweating, rhinorrhea, loose stools,
hiccups and anorexia" (p632) which many subjects compared to a bout of
influenza. These symptoms were reduced by the resumption of marijuana
use (Jones et al, 1981).

Georgotas and Zeidenberg (1979) reported similar withdrawal phenomena
in their long-term dosing study. During the first week of a four-week
wash-out period after four weeks of receiving 210mg of cannabis a day,
the subjects "became very irritable, uncooperative, resistant, and at
times hostile ... their desire for food decreased dramatically and
they had serious sleeping difficulties" (p430). These effects
disappeared during the final three weeks of the wash out. These
studies suggest that tolerance can develop to cannabis's effects and
that a withdrawal syndrome can occur on abstinence under certain
conditions, namely, chronic administration of doses as low as 10 mg
per day for 10 days (Jones et al, 1981).

The results of laboratory studies have received suggestive support
from a small number of studies of heavy cannabis users. Weller and
Halikas (1982), for example, found that the self-reported positive
effects of cannabis use diminished over a five to six-year period in
regular users of cannabis. The average reduction in the frequency of
experiencing the positive effects was small, perhaps because only 27
per cent were daily users, but they were consistent and included some
of the symptoms reported in laboratory studies.

The laboratory and observational studies raise the following
questions: How relevant are these observations to contemporary
cannabis users? How often does sufficient tolerance to cannabis
develop for users to experience a withdrawal syndrome? How often is
cannabis used to relieve or avoid withdrawal symptoms, and if so, does
such behaviour play any role in maintaining use and producing
dependence? These questions remain unanswered (Edwards, 1982; Jones,
1984), although (as will be seen below) there is clinical and
observational evidence that some heavy chronic users experience
tolerance and withdrawal symptoms, and that some use cannabis to
control these symptoms.



7.3.3 Clinical and observational evidence on dependence

There has not been an organised program of research on the cannabis
dependence syndrome comparable to that undertaken on the alcohol and
the opiate dependence syndromes. Instead, its existence and
characteristics have had to be inferred from a diverse body of
research studies. This comprises: limited data on the prevalence and
characteristics of persons seeking professional help in dealing with
their cannabis use and associated problems; a small number of
observational studies of problems reported by non-treatment samples of
long-term cannabis users; and a very small and recent literature
examining the validity of the cannabis dependence syndrome, usually as
part of larger investigations of the validity of the substance
dependence syndromes embodied in DSM-III-R and other classification
systems.

During the 1980s evidence began to emerge that there had been an
increase in the number of persons seeking help with cannabis as their
major drug problem. Jones (1984), for example, reported that 35,000
patients sought treatment in the United States in 1981 for drug
problems in which "cannabis was their primary drug" (p703), an
increase of 50 per cent over three years. Many of these patients
behaved "as if they were addicted to cannabis" and they presented
"some of the same problems as do compulsive users of other drugs"
(p711). More recently, Roffman and colleagues (1988) have reported a
strong response to a series of community advertisements offering help
to people who wanted to stop using marijuana.

Sweden, which has had a long history of hashish use, has also
experienced an increase in numbers of heavy hashish users presenting
to treatment services for assistance with problems caused by its use
(Engstrom et al, 1985). Tunving et al (1988) have described their
experience treating approximately 100 individuals per year who
presented to Swedish treatment services requesting help in controlling
their cannabis use. Although no data were reported on the proportion
of these individuals who satisfied the
DSM-III-R criteria for cannabis dependence, these patients typically
complained of symptoms which arguably would meet some of its criteria.
They reported, for example, that they had been unable to stop using
cannabis after having made several unsuccessful attempts to stop or
cut down, that they were frequently intoxicated, often every day, and
that they continued to use despite suffering adverse effects which
they recognised were connected with their cannabis use, such as
sleeplessness, depression, diminished ability to concentrate and
memorise, and blunting of emotions. Hannifin (1988) and Miller and
Gold (1989) have reported similar behaviour patterns among cannabis
users who have sought assistance.

In Australia, there are indications that some heavy cannabis users
request help in controlling their use. Didcott et al (1988), for
example, reported on the characteristics of 3,462 clients seen in 12
residential treatment services in New South Wales in 1985 and 1986.
They found that cannabis was identified as the "primary drug problem"
by 25 per cent of clients seen, second only to the opioid drugs, which
were so identified by 73 per cent of clients. Just over half of all
clients (52 per cent), the majority of whom were polydrug users,
identified their cannabis use as "a problem". The prevalence of
cannabis use as a principal drug problem was lower in a 1992 National
Census of Clients of Australian Treatment Service Agencies (Chen,
Mattick and Bailey, 1993). In this census cannabis use was the main
drug problem for 6 per cent of the 5,259 clients, fifth in order of
importance behind alcohol (52 per cent), opiates (26 per cent),
tobacco (9 per cent) and opiate/polydrug problems (7 per cent).

Suggestive evidence of cannabis dependence has emerged from a small
number of observational studies of regular cannabis users. Weller,
Halikas and Morse (1984), for example, followed up a cohort of 100
regular marijuana users who were first identified in 1970-1971, and
assessed them for alcohol and marijuana abuse using Feighner's
criteria for alcoholism and an analogous set of criteria for marijuana
(see Weller and Halikas, 1980). Their concept of abuse would arguably
have included most cases of dependence. They were able to interview 97
of their subjects about the amount and frequency of alcohol and
marijuana use, and their experience of problems related to the use of
both drugs. According to Feighner's criteria, 9 per cent of subjects
were alcoholic and 9 per cent were "abusers" of marijuana, with 2 per
cent qualifying for both diagnoses. The most common symptoms reported
among those classified as marijuana abusers were feeling "addicted", a
history of failed attempts to limit use, early morning use, and
traffic arrests related to marijuana use.

Hendin et al (1987) reported on the experiences of 150 long-term daily
cannabis users who had been recruited through newspaper
advertisements. Although they did not explicitly inquire about the
symptoms of a cannabis dependence syndrome, substantial proportions of
their sample reported experiencing various adverse effects of
long-term use, despite which they continued to use cannabis. These
included: impaired memory (67 per cent); an impaired ability to
concentrate on complex tasks (49 per cent); difficulty getting things
done (48 per cent); or thinking clearly (43 per cent); reduced energy
(43 per cent); ill health (36 per cent); and accidents (23 per cent).
Substantial minorities reported that it had impeded their educational
(31 per cent), and career achievements (28 per cent), and half of the
sample reported that they would like to cut down or stop their use.

These findings have been broadly supported by Kandel and Davies (1992)
and by Stephens and Roffman (1993). Kandel and Davies reported on the
characteristic problems reported by near daily cannabis users (aged
28-29 years) who were identified in a prospective study of the
consequences of adolescent drug use. The major adverse consequences of
use were: subjectively experienced cognitive deficits; reduced energy;
depression; and problems with spouse. Stephens and Roffman's sample of
users answering an advertisement offering assistance in quitting
cannabis complained of: "feeling bad about using"; procrastinating
because of their use; memory impairment; loss of self-esteem;
withdrawal symptoms; and spouse complaints about their use. In the
absence of control groups, however, it is impossible to be certain
that the prevalence of these symptoms is higher than in the community,
and that they were not present prior to cannabis use, as has been
reported in some longitudinal studies (e.g. Shedler and Block, 1990).

The most direct support for the validity of the cannabis abuse
dependence syndrome comes from a series of studies of the validity of
diagnostic criteria for substance dependence. Kosten et al (1987)
tested the extent to which the DSM-III-R psychoactive substance
dependence disorders for alcohol, cannabis, cocaine, hallucinogens,
opioids, sedatives and stimulants constituted syndromes. A sample of
83 persons (41 from an inpatient psychiatric unit and 42 from an
outpatient substance abuse treatment unit) was interviewed using a
standardised psychiatric interview schedule to elicit the symptoms of
drug dependence as defined in DSM-III-R for each of the drug classes.
Multiple diagnoses were allowed, so many individuals qualified for
more than one type of drug dependence.

There was consistent support for a unidimensional dependence syndrome
for alcohol, cocaine and opiates. The results were more equivocal in
the case of the cannabis dependence syndrome. All the items were
moderately positively correlated, had good internal consistency, and
seemed to comprise a Guttman scale, but a Principal Components
Analysis of the cannabis items suggested that (unlike alcohol, cocaine
and heroin, all of which had a single underlying factor) there seemed
to be three independent dimensions of dependence: compulsion indicated
by impaired social activity attributable to drug use, preoccupation
with drug use, giving up other interests, and using more than
intended; inability to stop use, indicated by not being able to cut
down the amount used, rapid reinstatement after abstinence, and
tolerance to drug effects; and withdrawal identified by withdrawal
symptoms, use of cannabis to relieve withdrawal symptoms, and
continued use despite problems.

Two more recent studies on much larger samples have provided stronger
support for the concept of a cannabis dependence syndrome. Newcombe
(1992) reported factor analyses of 29 questionnaire items designed to
measure DSM-III-R abuse and dependence for a community sample of 614
young adults reporting on their use of alcohol, cocaine, and cannabis.
He reported a strong common factor for all three drug types which
accounted for 36 per cent to 40 per cent of the item variance.
Rounsaville, Bryant, Babor, Kranzler and Kadden (1993) report the
results of factor analyses of items designed to assess dependence in
each of three diagnostic systems (DSM-III-R. DSM-IV and ICD-10) for
each of six drug classes (alcohol, cocaine, marijuana, opiates,
sedatives and stimulants). Their sample comprised 521 persons
recruited from inpatient and outpatient drug treatment, psychiatric
treatment services, and the general community. They found that a
single common factor explained the variation between diagnostic
criteria for all diagnostic systems, and for all drug types.



7.3.4 Epidemiological evidence on cannabis abuse and dependence

The best evidence on the prevalence of cannabis abuse and dependence
in the community comes from the Epidemiological Catchment Area (ECA)
study (Robins and Regier, 1991) which involved face-to-face interviews
with 20,000 Americans in five catchment areas: Baltimore, Maryland;
Los Angeles, California; New Haven, Connecticut; Durham, North
Carolina; and St Louis, Missouri. A standardised and validated
clinical interview schedule was used to elicit a history of
psychiatric symptoms found in 40 major psychiatric diagnoses,
including drug abuse and dependence. This information was used to
diagnose the presence or absence of a DSM-III diagnosis of drug
dependence (Anthony and Helzer, 1991). Although not a true random
sample of the American population, it is the best available data on
the prevalence of different types of drug dependence and their
correlates in a non-treatment population.

Illicit drug use was defined as "any non-prescription psychoactive
agents other than tobacco, alcohol and caffeine, or inappropriate use
of prescription drugs" (Anthony and Helzer, 1991, p116). To exclude
individuals who had only briefly experimented with illicit drugs,
individuals had to have used an illicit drug on more than five
occasions before they were asked about any symptoms of drug
dependence. The focus of the interview schedule was on the "consequent
psychiatric symptoms and behavioral changes that constitute the
syndromes of drug abuse and dependence" (p117).

The criteria used to define drug abuse and dependence were derived
from the DSM-III, which divided symptoms of abuse and dependence into
four main groups: (1) tolerance to drug effects; (2) withdrawal
symptoms; (3) pathological patterns of use; and (4) impairments in
social and occupational functioning due to drug use. Drug abuse
required a pattern of pathological use and impaired functioning. In
the case of cannabis, a diagnosis of dependence required pathological
use, or impaired social functioning, in addition to either signs of
tolerance or withdrawal. The problem had to have been present for at
least one month, although there was no requirement that all criteria
had to be met within the same period of time. In reporting the results
Anthony and Helzer report the prevalence of abuse and/or dependence
combined for all drug types.

Illicit drug use was relatively common in the sample, with 36 per cent
of persons having used at least one illicit drug. Cannabis was the
most commonly used illicit drug, having been used by 76 per cent of
those who had used any illicit drug more than five times. Drug abuse
and dependence were relatively common, with 6.2 per cent of the
population qualifying for such a diagnosis. Cannabis abuse and/or
dependence was the most common form of abuse and/or dependence, with
4.4 per cent of the population being so diagnosed compared with 1.7
per cent for stimulants, 1.2 per cent for sedatives, and 0.7 per cent
for opioid drugs. Two-thirds of cases of cannabis abuse and/or
dependence had used cannabis within the past year, and half had used
within the past month. "Almost two-fifths (38 per cent) of those with
a lifetime history of cannabis abuse and/or dependence reported active
problems in the prior year" (Anthony and Helzer, 1991, p123)

When DSM-III-R diagnoses of dependence and abuse were approximated,
three fifths of those with a diagnosis of dependence and/or abuse met
the criteria for dependence. The proportion of current users who were
dependent increased with age, from 57 per cent in the 18-29 year age
group to 82 per cent in the 45-64 year age group, reflecting the
remission of less severe drug abuse problems with age. Only a minority
of those who had a diagnosis of abuse and/or dependence (20 per cent
of men and 28 per cent of women) had mentioned their drug problem to a
health professional, even though 60-70 per cent had sought medical
treatment in the previous month. There were predictable age and gender
differentials in prevalence of drug abuse and/or dependence. Men had
higher prevalence than women (7.7 per cent versus 4.8 per cent). This
was largely due to differences in exposure to illicit drugs, since the
prevalence of a diagnosis of abuse and/or dependence among persons who
had used an illicit drug more than five times was the about the same
for men and women (21 per cent and 19 per cent). The highest
prevalence of abuse and/or dependence (13.5 per cent) was in the 18-29
year age group (16.0 per cent among men and 10.9 per cent among
women), declining steeply thereafter in both sexes.

It is difficult to make clear inferences about the prevalence of
cannabis dependence in the community from the ECA study, because
DSM-III rather than DSM-III-R criteria were used, and the data on the
prevalence of drug abuse and/or dependence have not been broken down
either by abuse and dependence or by drug class. The first of these
problems may not be too serious, since studies comparing DSM-III and
DSM-III-R criteria (e.g. Rounsaville et al, 1987) suggest that there
is reasonable agreement between a DSM-III diagnosis of abuse or
dependence and DSM-III-R dependence, in the case of cannabis
dependence. Any disagreements in diagnosis seem to be in the direction
of DSM-III-R identifying more cases as dependent than DSM-III,
suggesting that any errors in the prevalence of drug abuse in the ECA
study will be in the direction of underestimation.

The absence of detailed ECA reports on the separate prevalence of drug
abuse and dependence is more difficult to circumvent. If we assume
that any differences between drug types in the proportion of users who
became dependent would have been reported (and hence that the ratio of
cases of dependence to abuse for cannabis is 3:2), then the prevalence
of cannabis dependence in the USA in 1982-1983 would have been 2.6 per
cent of the population. If we also assume that the ratio of cases of
cannabis dependence to cases of cannabis abuse was the same for men
and women, then 3.2 per cent of men and 2.0 per cent of women would
have been diagnosed as cannabis dependent.

Similar estimates of the population prevalence of cannabis dependence
were produced by a community survey of psychiatric disorder conducted
in Christchurch, New Zealand, in 1986, using the same sampling
strategy and diagnostic interview as the ECA study (Wells et al,
1992). This survey used the DIS to diagnose a restricted range of
DSM-III diagnoses in a community sample of 1,498 adults aged 18-64
years of age. The prevalence of having used cannabis on five or more
occasions was 15.5 per cent, remarkably close to that of the ECA
estimate, as was the proportion who met DSM-III criteria for marijuana
abuse or dependence, namely 4.7 per cent. The fact that this survey
largely replicated the ECA findings for most other diagnoses,
including alcohol abuse and dependence, enhances confidence in the
validity of the ECA study findings.



7.3.5 The risk of cannabis dependence

It is important to put the existence of a cannabis dependence syndrome
into perspective to avoid a falsely alarmist impression that all
cannabis users run a high risk of becoming dependent upon cannabis. A
variety of estimates suggest that the crude risk is small, and
probably more like that for alcohol rather than nicotine or the
opioids. Other data suggests that certain characteristics of users
increase the risk of dependence developing, although in most cases it
is impossible to place quantitative estimates on the latter risks.

As with all drugs of dependence, persons who use cannabis on a daily
basis over periods of weeks to months are at greatest risk of becoming
dependent upon it. The ECA data suggested that approximately half of
those who used any illicit drug on a daily basis satisfied DSM-III
criteria for abuse or dependence (Anthony and Helzer, 1991). Since
this estimate was based upon drug abuse and dependence for all drug
types, including opioids, it probably overestimates the risks of
dependence among daily cannabis users. Kandel and Davis (1992)
estimated the risk of dependence among near daily cannabis (according
to approximated DSM-III criteria) at one in three.

The risk of developing dependence among less frequent users of
cannabis, including experimental and occasional users, would be
substantially less than that for daily users. A number of reasonably
consistent estimates of the risks of a broader spectrum of users
becoming dependent on cannabis can be obtained from recent studies. A
crude estimate from the ECA study was that approximately 20 per cent
of persons who used any illicit drug more than five times met DSM-III
criteria for drug abuse and dependence at some time. The specific rate
of abuse and dependence for cannabis (calculated by dividing the
proportion who met criteria for abuse and dependence by the proportion
who had used the drug more than five times) was 29 per cent. A more
conservative estimate which removed cases of abuse (40 per cent) from
the overall estimate of cannabis abuse and dependence would be that 17
per cent of those who used cannabis more than five times would meet
DSM-III criteria for dependence.

Estimates derived from a number of other studies suggest that the ECA
estimates of the risk of dependence are reasonable. The crude
percentage of cases of dependence and abuse among persons who had used
cannabis five or more times in the Christchurch epidemiology study
(Wells et al, 1992) was 30 per cent, while an estimate derived from
Newcombe's community survey of young adults was 25 per cent of those
who had ever used cannabis. A comparable estimate can be derived from
Kandel and Davies' (1992) study of near daily cannabis users. [This
was done by multiplying the ECA estimate of the proportion of daily
users who met criteria for abuse and dependence (50 per cent) by the
proportion of near daily users in Kandel and Davis sample (44 per
cent), and adding this to the ECA estimate of the proportion of
non-daily illicit drug users who met the criteria (30 per cent)
multiplied by their proportion in the Kandel and Davies sample (55 per
cent)]. On Kandel and Davies data the estimated rate of abuse and
dependence among those who had used cannabis 10 or more times was 39
per cent, the higher rate reflecting the higher number of times of use
required to be counted as a cannabis user in Kandel and Davies study
(10 times versus five times in ECA). A lower estimate of 12 per cent
for DSM-III-R cannabis dependence was obtained by McGee and colleagues
(1993) in a prospective study of 18-year-old youth in Dunedin, New
Zealand. A lower estimate was to be expected given the youth of the
sample, and the fact that the estimate is the proportion of dependent
users among those who had ever used cannabis.

Although one would not want to claim a great deal of precision for any
of these individual estimates of the risk of cannabis dependence, it
is reassuring that they are within a range of 12-37 per cent, and that
the estimates vary in predictable ways with the ages of the samples
and the stringency of the criteria used in defining cannabis use. The
reasonable consistency of the estimates suggests the following rules
of thumb about the risks of cannabis dependence. For those who have
ever used cannabis, the risks of developing dependence is probably of
the order of one chance in 10. The risk of dependence rises with the
frequency of cannabis use, as it does with all drugs, so that among
those who use the drug more than a few times the risk of developing
dependence is in the range of from one in five to one in three. The
range of the estimates reflects variations in the number of occasions
of use that is taken to reflect more than simple experimentation, with
the general rule being that the more often the drug has been used, and
the longer the period of use, the higher is the risk of becoming
dependent. Although there have been few formal comparisons of the
dependence potential of cannabis with that of other drugs, these risks
are probably more like those associated with alcohol than those
associated with tobacco and opiates (Woody, Cottler and Cacciola,
1993).

Apart from frequency of use, other risk factors have been identified
in the series of prospective studies of adolescent illicit drug use
reviewed above. These include the following factors which have been
shown to predict continued use and more intensive involvement with
illicit drugs: poor academic achievement; deviant behaviour in
childhood and adolescence; nonconformity and rebelliousness; personal
distress and maladjustment; poor parental relationships; earlier use;
and a parental history of drug and alcohol problems (Brook et al,
1992; Kandel and Davies, 1992; Newcombe, 1992; Shedler and Block,
1990). For most of these variables it is difficult to attach any
quantitative estimates to the increased risk of dependence, because
they have been measured in different ways in different studies.

These overall statements of the risks of cannabis dependence ignore
the fact that the risk of dependence is not equally distributed in the
population. The ECA study suggested that men have a higher risk of
developing dependence than women, and that the risk was highest among
the younger 18-29 year old cohort. In both cases, however, the most
likely explanation was the different rates of exposure to cannabis
among men and women, and among younger and older persons (Anthony and
Helzer, 1991). When this was controlled by looking at the rates of
dependence among daily users of the drug among men and women and
younger and older persons, the differences in the risk of dependence
largely disappeared (Anthony and Helzer, 1991).



7.3.6 The consequences of cannabis dependence

Another important issue that needs to be considered when placing the
risks of cannabis dependence into perspective is that of the
consequences of developing dependence. How easy or difficult is it for
those who decide to stop using cannabis to achieve and maintain
abstinence? This question is difficult to answer in the absence of
systematic research on the natural history of cannabis dependence. The
following are reasonable inferences about what the rate of remission
might be. First, cannabis dependence resembles alcohol dependence in
the risk of dependence, and the similarity in the age and gender
distributions of heaviest use, and abuse, and dependence. It seems
reasonable then to suppose that there is likely to be a high rate of
remission without treatment in cannabis dependence, as there is in as
in alcohol dependence in the community (Helzer, Burnham and McEvoy,
1991). The large discrepancy between the ECA estimates of cannabis
abuse and dependence in the community, and the proportions of cannabis
users among drug users seeking treatment provides indirect support for
this inference. Kandel and Davies' (1992) findings provide more direct
support. They found that 44 per cent of those who had used cannabis
more than 10 times became near daily users for an average period of
three years. Yet by age 28-29, less than 15 per cent of those who had
ever been daily users were still daily users, indicating a very high
rate of remission during the 20s.

Among those who develop cannabis dependence, how disruptive to
everyday life and functioning is it? This is even more difficult to
answer. All that can be said with confidence is that there are some
cannabis users who are sufficiently troubled by the consequences of
their dependence to seek assistance. The experience of Roffman and
colleagues suggests that this number may be increased if more effort
was made to attract dependent cannabis users into treatment. Among the
population of cannabis dependent persons seeking treatment, the major
complaints have been the loss of control over their drug use,
cognitive and motivational impairments which interfere with
occupational performance, lowered self-esteem and depression, and the
complaints of spouses and partners (see above). There is no doubt that
some dependent cannabis users report impaired performance and a
reduced enjoyment of everyday life, but more detailed research is
necessary to make a better judgment about how common this is, and how
severe the impairment typically produced by cannabis dependence is.

7.3.7   The treatment of cannabis dependence

Given the widespread scepticism about the existence of a cannabis
dependence syndrome, the question of what should be done to assist
those who present for help with their cannabis use has largely been
ignored (see Kleber, 1989). Indeed, Stephens and Roffman (1993) have
suggested that there is a widespread view among drug and alcohol
treatment practitioners that cannabis dependence does not require
treatment because the withdrawal syndrome is so mild that most users
can quit without assistance. Although, as argued above, it is likely
that rates of remission without treatment are substantial, the fact
that many users succeed without professional assistance does not mean
we should ignore requests for assistance from those who are unable to
stop on their own. As with persons who are nicotine dependent, those
dependent cannabis users who have repeatedly failed in attempts to
stop their cannabis use need professional assistance to do so. But
what types of treatment should be offered?

There is not a lot of information on which to base useful
recommendations. The available literature largely consists of
treatment suggestions based upon personal experience, or upon clinical
wisdom derived from opinions about the best forms of treatment for
other related forms of dependence, such as alcohol and tobacco (e.g.
de Silva, DuPont, and Russell, 1981). Jones (1984), for example,
suggested that because cannabis was usually smoked in social settings,
the treatment for cannabis dependence should be based upon principles
derived from successful forms of treatment for nicotine dependence.
Such treatment would include: assisted cessation of cannabis use
accompanied by education about the acute and chronic effects of the
drug; social skills training in resisting the social cues for cannabis
use; and the mobilisation of peer support to maintain abstinence
through self-help groups.

Others have preferred to adopt approaches adapted from those developed
to treat alcohol dependence. Hannifin (1988), in arguing for the
concept of "cannabism" by analogy to "alcoholism", implied that it be
managed in much the same way. Miller and his colleagues (Miller and
Gold, 1989; Miller, Gold and Pottash, 1989) have recommended a
treatment model based upon the preferred form of treatment for alcohol
dependence in the United States, namely, detoxification, a 12-step
program delivered during an extended inpatient stay, and enrolment in
Alcoholics Anonymous or Narcotics Anonymous after discharge. Stephens
and Roffman (1993) and Zweben and O'Connell (1992) have suggested
eclectic approaches combining management of withdrawal, relapse
prevention methods, and enrolment in 12-step programs. Tunving et al
(1988) have described their experience with a similar eclectic
outpatient program for cannabis users in Sweden. De Silva et al (1981)
provide short accounts of a variety of treatment approaches for
marijuana dependent adolescents.

There have been very few controlled evaluations of the effectiveness
of these recommendations. Smith et al (1988) reported a simple
pre-treatment and post-treatment comparison of cannabis use among
patients who received outpatient aversion therapy and group
self-management counselling. They found good self-reported rates of
abstinence, but these were obtained from telephone interviews
conducted by the therapists who delivered the treatment. Roffman et al
(1988) have reported a randomised controlled trial comparing group
based relapse prevention or social support. Subjects were 120 men and
women (average age 32 years with an average history of 16 years
marijuana use) who had answered advertisements publicising a treatment
program for adults seeking help to stop using marijuana. Their results
at one month follow-up were much less positive than those of Smith et
al: only 30 per cent of their patients were still abstinent, although
75 per cent had set abstinence as a treatment goal. By the end of a
year the abstinence rate had dropped to 17 per cent. Results were a
little more positive when evaluated in terms of average number of days
of use, and in problems experienced, suggesting that the outcome of
cannabis cessation treatment is much like that for alcohol and tobacco
(Heather and Tebbutt, 1989).

Much more research is clearly required before sensible advice can be
given about the best ways to achieve abstinence from cannabis. In the
absence of better evidence of treatment effectiveness, those who offer
treatment for cannabis dependence should avoid replicating experience
in the alcohol field, where intensive and expensive forms of inpatient
treatment have been widely adopted in the absence of any good evidence
that they are more effective than less intensive outpatient forms of
treatment (Heather and Tebbut, 1989; Miller and Hester, 1986).



7.3.8 Conclusions

In 1982 Edwards reviewed the available evidence on the question of
whether there was a cannabis dependence syndrome as defined by the
1981 World Health Organisation criteria. Although he argued that there
was good evidence of tolerance and a withdrawal syndrome, there was
insufficient evidence bearing on the criteria of compulsion, narrowing
of repertoire, reinstatement after abstinence, use to relieve or
prevent withdrawal symptoms and salience of cannabis use. He added
that although tolerance and withdrawal were insufficient to prove the
existence of a dependence syndrome, they nonetheless constituted
"grounds for believing that such a syndrome may exist" (p38). Until
these issues were resolved, he concluded, the question remained "very
open".

On the basis of evidence gathered since Edwards wrote, we conclude
that there probably is a cannabis dependence syndrome like that
defined in DSM-III-R which occurs in heavy chronic users of cannabis.
There is good experimental evidence that chronic heavy cannabis use
can produce tolerance and withdrawal symptoms, and some clinical and
epidemiological evidence that some heavy cannabis users experience
problems controlling their cannabis use, and continue to use despite
the experience of adverse personal consequences of use. There is
reasonable observational evidence that there is a cannabis dependence
syndrome like that for alcohol, cocaine and opioid dependence. If the
estimates of drug dependence from the ECA study are approximately
correct, cannabis dependence is the most common form of dependence on
illicit drugs, reflecting its high prevalence of use in the community.
The risk of developing the syndrome is probably of the order of: one
chance in ten among those who ever use the drug; between one in five
and one in three among those who use more than a few times; and around
one in two among those who become daily users of the drug.

Recognition of the cannabis dependence syndrome has been delayed
because of its apparent rarity in Western societies, which reflects a
number of factors. First, heavy daily cannabis use has been relatively
uncommon by comparison with the intermittent use of small quantities
of cannabis. Second, until recently there have been few individuals
who have presented requesting assistance for cannabis related
problems. This may have been because it is easier to stop using
cannabis than opioids or alcohol without specialist assistance, or it
may be that the impact of cannabis dependence on the user is not as
transparently adverse as that of alcohol or opioid problems to users
and their families. Third, an overemphasis on the occurrence of
tolerance and a withdrawal syndrome in the past has hindered its
recognition in those individuals who have presented for treatment.
Fourth, cannabis dependence (which is widespread among opioid
dependent persons) has been perceived to be a less serious problem
than dependence on alcohol, opioids and stimulants, which have
accordingly been given priority in treatment (Hannifin, 1988).

Given the widespread use of cannabis, and its continued reputation as
a drug which is free of the risk of dependence, the clinical features
of cannabis dependence deserve to be better delineated and studied.
This would enable its prevalence to be better estimated, and
individuals with this dependence to be better recognised and treated.
Treatment should probably be on the same principles as what is
effective for other forms of dependence. Treatment for tobacco
dependence may provide a better model than treatment for alcohol
dependence, although this area is in need of research.

Although cannabis dependence is likely to be a larger problem than
previously thought, we should be wary of over-estimating its social
and public health importance. It will be most common in the minority
of heavy chronic cannabis users. Even in this group, the prevalence of
drug-related problems may be relatively low by comparison with those
of alcohol dependence, and the rate of remission without formal
treatment is likely to be high. While acknowledging the existence of
the syndrome, we should avoid exaggerating its prevalence and the
severity of its adverse effects on individuals. Better research on the
experiences of long-term cannabis users should provide more precise
estimates of the risk.



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7.4 Effects of chronic cannabis use on cognitive functioning

Because cannabis use acutely impairs cognitive processes, a concern
has arisen that chronic cannabis use may cause chronic cognitive
impairment. Such a chronic effect need not necessarily be permanent,
but it would persist beyond the elimination of cannabinoids from the
body, and hence would be the result of secondary changes induced by
cumulative exposure to cannabinoids. Such chronic effects could
produce relatively enduring behavioural deficits which presumably
reflect changes in brain function.

This chapter deals with the evidence from a variety of different types
of study about the cognitive effects of chronic cannabis use. The
caveats mentioned in the introduction must be born in mind whilst
critically assessing this evidence: many other factors must be
controlled in order to confidently attribute any cognitive effects to
cannabis use. Among these, the most important are ensuring that the
cognitive impairment did not precede cannabis use, and ensuring that
the cognitive effects are not the result of the multiple drug use that
is especially common among heavy cannabis users (Carlin, 1986).



7.4.1 Clinical observations

Concerns about the cognitive effects of chronic cannabis use during
the early 1970s were first prompted by clinical reports of mental
deterioration in persons who had used cannabis heavily (at least
daily) for more than one year (Fehr and Kalant, 1983). Kolansky and
Moore (1971, 1972), for example, reported cases of psychiatric
disorder in adolescents and young adults (38 cases) and among adults
(13 cases) who had used marijuana at least twice per week. The
clinical picture was one of "very poor social judgment, poor attention
span, poor concentration, confusion, anxiety, depression, apathy,
passivity, indifference and often slowed and slurred speech" (Kolansky
and Moore, 1971). Cognitive symptoms included: apathetic and sluggish
mental and physical responses; mental confusion; difficulties with
recent memory; and incapability of completing thoughts during verbal
communication. These symptoms typically began after cannabis use and
disappeared within three to 24 months of abstinence. The course and
remission of symptoms also appeared to be correlated with past
frequency and duration of cannabis smoking. Those with a history of
less intensive use showed complete remission of symptoms within six
months; those with more intensive use took between six and nine months
to recover; while those with chronic intensive use were still
symptomatic nine months after discontinuation of drug use.

These clinical reports, similar observations by Tennant and Groesbeck
(1972) among hashish smoking US soldiers in West Germany, and a report
of cerebral atrophy in young cannabis users (Campbell et al, 1971)
excited substantial controversy about the cognitive effects of chronic
cannabis use. Critics were quick to object to the lack of objective
measures of impairment and the biased sampling from psychiatric
patient populations. It was also difficult to rule out alternative
explanations of the apparent association between cannabis use and
cognitive impairment, namely, that many of these effects either
preceded cannabis use, or were the result of other drug use. Whatever
their limitations, these clinical reports alerted the community to the
possible risks of using cannabis when it was becoming popular among
the young in Western countries; they also prompted better controlled
empirical research on the issue.



7.4.2 Cross-cultural studies

In response to public anxiety about the increase in marijuana use in
the late 1960s, the National Institute on Drug Abuse (NIDA) in the
United States commissioned three cross-cultural studies in Jamaica,
Greece and Costa Rica to assess the effects of chronic cannabis use on
cognitive functioning (among other things). The rationale for these
studies was that any cognitive effects of chronic daily cannabis use
would be most apparent in cultures with a long-standing tradition of
heavy cannabis use.



7.4.2.1 Jamaica

Bowman and Pihl (1973) conducted two field studies of chronic cannabis
use in Jamaica, one with a small sample of 16 users and 10 controls
from rural