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Major Studies of Drugs and Drug Policy
The Report of the Canadian Government Commission of Inquiry into the Non-Medical Use of Drugs - 1972


The Report of the Canadian Government Commission of Inquiry into the Non-Medical Use of Drugs - 1972

2. Cannabis and Its Effects


Some Subjective Characteristics of the Cannabis 'High'

The subjective psychological effects of cannabis vary greatly with a number of factors and are often difficult to predict. The dose, type of preparation, and rate and mode of administration can often greatly influence the response. Furthermore, the psychological effects depend to a considerable degree on the personality of the user, his past experience with cannabis or other drugs, his attitudes, the setting in which the drug is used and other idiosyncratic factors. The response of the naive subject may be much more variable and unpredictable than that of an experienced user. Recently Jones has shown significant differences between the effects of standard doses of marijuana given subjects in isolation and in groups in the same laboratory setting. 303

Becker has suggested that the nature of the cannabis 'high' traditionally depends on a number of social and learning factors. An individual must first learn the proper technique of smoking cannabis; he must learn to recognize some of the more subtle aspects of the subjective effects; and thirdly, because cannabis effects are not necessarily inherently pleasurable, the novice user must often learn to enjoy the response he has come to recognize as cannabis induced. In different situations, the effects experienced may be socially defined as positive or negative.39,40,42 This analysis is extended to adverse psychological reactions in a later section of this chapter.

Although hashish may be many times more potent than marijuana, the effects of these two forms of cannabis, as usually used in North America, are generally similar and often indistinguishable. It has been reported that most experienced individuals smoke to attain a certain effect or level of 'high', and adjust the dose according to the potency of the substance used. 'Grass' and 'hash' are generally used interchangeably in Canada. Although it is generally easier to consume excessive quantities of THC in the form of hashish, great variations in potency of different samples are usually accommodated by the experienced user through a "titration" of dose (intake is reduced or stopped when the smoker reaches the preferred level of intoxication). Comparable precision is generally not possible with cannabis taken orally, however, due to the long delay in action, and a "non-optimal" effect is therefore more likely to occur with this mode of administration. Both the phenomenon of "self titration" and the equivalence of the marijuana and hashish 'high' have not been well explored in the laboratory. In some Eastern countries, different social norms have evolved around the different forms of cannabis, and the pattern of drug use associated with bhang drinks may be quite different from that seen with the smoking of hashish. Long-term heavy cannabis users invariably prefer the more potent ganja or hashish.

It is often difficult to find descriptions of the subjective effects of marijuana that are free from value judgements. Many effects seem to take on good or bad connotations depending on the circumstances in which they occur, the personal attitudes of the individual undergoing the experience, and the orientation of the observer who is recording them. Moreover, since many of the significant psychological effects are intensely personal, the laboratory scientist often has little opportunity to make objective measurements, and must rely on subjective, introspective reports communicated verbally through a language system which is frequently inadequate.

As noted earlier, some investigators object to cannabis being classified with LSD and similar substances. It is often suggested that marijuana is a mild intoxicant, more like alcohol. It is clear, however, that high doses of cannabis, in some individuals, may produce effects somewhat similar to an attenuated LSD experience. While such effects are rarely reported, many milder aspects of the psychedelic experience regularly occur with a cannabis 'high'. The outline of potential reactions to psychedelic drugs presented in the Commission's Interim Report 106,483 include: psychotic and non-psychotic adverse reactions, psychodynamic, cognitive, aesthetic, and psychedelic-peak (transcendental) or religious experiences. While analogous experiences may occur in varying degrees with cannabis, the quality of the effects is reportedly different and, in general, the intensity of psychedelic effects is considerably lower and the overall response more controllable than with the more potent psychedelic drugs. It would be incorrect to say that cannabis in moderate doses actually produces a mild LSD experience; the effects of these two drugs are physiologically, behaviourally and subjectively quite distinct. Furthermore, since no cross-tolerance occurs between LSD and THC, the mechanism of action of the two drugs is thought to differ.297,631 

Although the altered state of consciousness produced by cannabis is undoubtedly multi-dimensional, as Tart has argued,598 there seems to be a common factor of 'highness' which can be reliably rated by subjects under certain laboratory and social situations. However, there is currently considerable controversy regarding the ability of even regular users to discriminate among different doses of cannnabis and similar but inactive placebo material.111,298,303,397,399,400,431 While many of the subjective effects of cannabis are obviously difficult to quantify, subjects in Commission experiments were fairly efficient at differentiating the various doses on subjective indices and were not deceived for long by the placebo. Clear dose and time-response effects were seen on a simple "highness" rating scale, and subjective measures correlated significantly with a number of objective behavioural and physiological variables. Some of the inconsistencies in the literature with respect to the reliability of subjects' phenomenological evaluations in the laboratory are probably due, at least in part, to the lack of standardized smoking techniques in most experiments.

The role of learning in the subjective effects of cannabis is perhaps most apparent in the phenomenon often referred to as a 'contact high'. Persons familiar with cannabis use may report feeling some of the milder subjective effects of the drug, without using it, when they are interacting with persons who are 'high'. Similar occurrences have been reported with other drugs, including alcohol.

A cannabis 'high' typically involves numerous phases. The initial effects are often somewhat stimulating and, in some individuals, may elicit mild tension or anxiety which is usually replaced by a pleasant feeling of well being. The later effects usually tend to make the user introspective and tranquil. Rapid mood changes often occur. A period of enormous hilarity may be followed by a contemplative silence. Many users report that they have some control over the degree to which they are involved in the subjective effects and that, when necessary, they can 'come down' and perform normally. Such a phenomenon may account for some of the discrepancies which exist between the substantial subjective changes that are often reported in the absence of significant objectively verifiable behavioural effects. The ability of subjects to 'come down' at will has not been adequately explored experimentally.

Subjective effects which are typically reported by users include: happiness, Increased conviviality, a feeling of enhanced interpersonal rapport and Communication, heightened sensitivity to humour, free play of the imagination, unusual cognitive and ideational associations, a sense of extraordinary reality, a tendency to notice aspects of the environment of  which one is normally unaware, enhanced visual imagery, altered sense of time in which minutes may seem like hours, changes in visually perceived spatial relations, enrichment of sensory experiences (subjective aspects of sound and taste perception are often particularly enhanced), increased personal understanding and religious insight, mild excitement and energy (or just the opposite), increased or decreased behavioural activity, increased or decreased verbal fluency and talkativeness, lessening of inhibitions and emotional control, and at higher doses, a tendency to lose or digress from a train of thought. Feelings of enhanced spontaneity and creativity are often described, although an alteration in creative performance is difficult to establish scientifically. While most experts agree that cannabis has little specific aphrodisiac (sex-stimulating) effect, many users report increased enjoyment of sex and other intimate human contact while under the influence of the drug. 227,232,238,239,249,349,350,351,438,440,481,598

Unpleasant experiences may occur in different individuals, or possibly in the same individual at different times, although significant acute adverse effects are relatively infrequent. Apparently most regular cannabis users have experienced some undesirable side effects from the drug.

Some of these reactions may include: fear and anxiety, depression, irritability, nausea, headache, cold hands and feet, backache, dizziness, blurred vision, a dulling of attention, confusion, lethargy, and a sensation of heaviness, weakness and drowsiness. Disorientation, depersonalization, delusions, suspiciousness, paranoia and, in some cases, panic, loss of control, and acute psychotic and depressive reactions have also been reported. Schwarz has compiled an extensive catalogue of reports of negative effects 541 which have at different times been attributed to cannabis in the literature. Adverse psychological reactions to cannabis are discussed in more detail in a separate section below.

Experimental Evidence of Sensory-Perceptual Effects 

Attempts to objectively demonstrate in the laboratory the phenomenological experiences described by users have met with mixed success. Little research has been done using modern signal detection methods, and the majority of studies have focussed on rather gross sensory aspects of the perceptual phenomenon of ultimate interest.

At moderate doses, cannabis users often report a feeling of improved visual clarity and acuity. At high doses, some blurred vision and difficulty with focussing may be noted and, occasionally, users report decreased or intensified depth perception.598 Experimental attempts to demonstrate effects in visual acuity and depth perception have found no consistent change, however.134,455 In a Commission experiment there was a suggestion of decreased depth perception with the higher marijuana dose, but no effect was seen on general visual acuity.518 Caldwell found no cannabis effects on brightness discrimination at apparently low doses.98 These visual functions should be further explored utilizing signal detection techniques. 236

In a pilot study which has received considerable publicity, Frank and associates suggested that visual recovery from bright-light glare was delayed by several seconds after marijuana smoking.199 It was implied that this increase in recovery time might increase the danger of night driving after cannabis use. However, later statistical analysis of the data showed no significant effect.263 Furthermore, in the same study, marijuana did not produce any change in illumination threshold. In another pilot study. these same investigators found no cannabis effects on simple dark adaptation.263 An exploratory study by the Commission using five subjects, run twice with a moderate dose of marijuana and twice on placebo, also found no statistically significant effect of marijuana on the recovery of dim-light visual acuity after bright-light glare.603 In addition, in a more comprehensive experiment using higher doses, Moskowitz found no cannabis effects on glare-recovery.455 Some cannabis users have reported a subjective sensation that visual after-images are retained for a longer period of time when 'high'. This effect might be explained by the general tendency of subjects to overestimate the passage of time after taking cannabis.

In a Commission experiment a significant improvement in two-flash fusion threshold (a measure of temporal acuity) was found one hour after subjects smoked cannabis.40 No change was seen in the Archimedes rotating spiral visual after-image test in this study. An enhancement of visual evoked cortical potential 611suggests some alteration in visual sensation with cannabis.

Almost uniformly reported by users are a variety of changes in eyes-closed visual imagery even in persons who rarely experience the phenomenon normally. In Commission experiments, dose-dependent increases in vividness, clarity, colour, movement, depth and complexity of eyes-closed visual imagery were demonstrated.558 In a few instances at the higher dose, synesthesia was reported (some imagery contained qualities experienced through other senses as well). This phenomenological analysis confirms the view that cannabis produces visual imagery changes somewhat similar to those reported with mescaline and LSD. 293,342,366,454,557 In rare instances, usually involving very high doses, eyes-open imagery or visual hallucinations may be seen with cannabis .324

Increased sensitivity to sound and greater appreciation of the subtleties of music are widely reported by cannabis users. While these subjective phenomena are not readily amenable to laboratory testing, simple sensory tests have found only minor and inconsistent changes in both directions in a variety of auditory differential discriminations and thresholds.98,134,461,670

Cannabis users frequently report an increased sensitivity to, and awareness of touch. While some investigators have found indication of enhanced sensation on certain measures,527 little or no change has been found in most laboratory experiments.564 Cannabis has been widely used in the past as a pain reducer. Its analgesic effects may not apply to all types of pain, however, and in some situations cannabis might even increase sensitivity to pain. In one continuing study, cannabis was found to be an effective analgesic.631  Little systematic investigation has been done in this area, however. The analgesic effects of cannabis, alone and perhaps in conjunction with other analgesic drugs, may have considerable therapeutic potential and should be fully explored. In spite of common reports from cannabis users that taste sensations are greatly enhanced by the drug, in one laboratory experiment no change was found in taste and olfactory sense.631,670 This is another area which has not been adequately explored.

Change in time perception is one of the most consistently reported features of the cannabis 'high'. Subjective time is almost invariably faster with the drug than without it, and cannabis usually results in an overestimate of the passage of clock time. Time production, rather than estimation, is less often affected.161[q] In some instances, subjects' estimates of clock time after marijuana are more accurate than with placebo, because of a normal tendency to underestimate time in certain conditions. All of these various time perception effects have been corroborated on different measures in Commission experiments.440,603 Time perception effects may be related to changes in short-term memory or may reflect a general speeding up of an "internal clock".

Caldwell and associates report that one of the more sensitive objective indices of a marijuana 'high' is an increase in the auto-kinetic effect 96 - a measure of apparent movement of a small stabilized light source in an otherwise dark environment. A similar increase in auto-kinesis was found in a Commission experiment. No consistent effect on the rod and frame test or other putative measures of field dependence have been reported in the literature.  111,282,308

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