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Marihuana, A Signal of Misunderstanding - Table of Contents

National Commission on Marihuana and Drug Abuse

Marihuana: A Signal of Misunderstanding

Chapter III

Social Impact of marihuana use

Marihuana and Violent Crime

As indicated earlier, the belief that marihuana causes or leads to the commission of violent or aggressive acts first emerged during the 1930's and became deeply embedded in the public mind. Until recently, however, these beliefs were generally based on the anecdotal case examples of law enforcement authorities, a few clinical observations and several quasi-experimental studies of selected populations comprised of military offenders, convicted or institutionalized criminals or delinquents and small groups of college students. Few efforts were made to compare the incidence of violent or aggressive behavior in representative samples of both user and non-user populations.

Even in these early observations and investigations, however, no substantial evidence existed of a causal connection between the use of marihuana and the commission of violent or aggressive acts. Indeed, if any relationship was indicated, it was not a positive and direct causal connection but in inverse or negative statistical correlation.

Rather than inducing violent -or aggressive behavior through its purported effects of lowering inhibitions, weakening impulse control and heightening aggressive tendencies, marihuana was usually found to inhibit the expression of aggressive impulses by pacifying the user, interfering with muscular coordination, reducing psychomotor activities and generally producing states of drowsiness lethargy, timidity and passivity.

In fact, only a small proportion of the marihuana users among any group of criminals or delinquents known to the authorities and appearing in study samples had ever been arrested or convicted for such violent crimes as murder, forcible rape, aggravated assaultor armed robbery. When these marihuana-using offenders were compared with offenders who did not use marihuana, the former were generally found to 'have committed less aggressive behavior than the latter.

In an effort to accumulate data on the relationship between marihuana use and aggressive or violent criminal behavior, the Commission sponsored several studies designed to assess the purported causal relationship.

First, the Commission wanted to tap the unique experience of the law enforcement and criminal justice communities. Representative samples of prosecuting attorneys, judges, probation officers and court clinicians were asked their opinions about the relationship between marihuana use and the commission of aggressive or violent criminal acts. When asked to evaluate the statement that "most aggressive acts or crimes of violence committed by persons who are known users of marihuana occur when the offender is under the influence of marihuana," three-quarters of the judges, probation officers and clinicians indicated either that the statement was probably untrue or that they were unsure of its accuracy. Of these three groups, a greater proportion of clinicians (76.5%) thought the statement false than did the probation officers (60%)and judges (44.2%).

In a separate mail survey of the chief prosecuting attorneys in the 50 states-the group which has often supported the causal hypothesis-52% of the respondents stated that they either did not believe or were uncertain of the truth of the proposition that use of marihuana leads to aggressive behavior.

We have already noted that only a small fraction of the offender populations in past studies were found to have been arrested for crimes of violence. Similarly, in a Commission-sponsored study of 1,776 16to-21-year-olds arrested in five New York counties for marihuana law violations between 1965 and 1969, onlv a small percentage bad either previously or subsequently come to the attention of authorities for such offenses as assault or robbery. In fact, less than 1% of the offenders in this sample had been arrested for these offenses prior to their first marihuana arrest, and less than 3% were known to the Federal Bureau of Investigation for these offenses subsequent to their marihuana violation.

Perhaps more important than professional opinion or the incidence of violent offenses in an offender population, however, is the determination of the extent to which marihuana use is related to violent or aggressive behavior in the general population.

In a Commission-sponsored survey, face-to-face interviews were conducted with a representative sample of 559 West Philadelphia residents in order to ascertain the extent of marihuana use in this heterogeneous population and the relative involvement of marihuana users and nonusers in violent criminal behavior. In corroboration of the earlier findings, the researchers found no significant differences in the proportions of users and non-users; who stated that they had committed any of the aggressive or violent crimes enumerated.

Further, no findings indicated that marihuana was generally or frequently used immediately prior to the commission of offenses in the very small number of instances in which these offense's did occur. In contrast, however, the aggressive and violent offenders in this sample did report with significantly greater frequency the use of alcohol within 24 hours of the offense in question.

These findings should be considered in fight of an earlier West Coast study of disadvantaged minority-group youthful marihuana users, many of whom were raised in a combative and aggressive social milieu similar to that found in several of the West Philadelphia sampled neighborhoods. The data show that marihuana users were much less likely to commit aggressive or violent acts than were those who preferred amphetamines or alcohol. They also show that most marihuana users were able to condition themselves to avoid aggressive behavior even in the face of provocation. In fact, marihuana was found to play a significant role in youth's transition from a "rowdy" to a "cool," non-violent style.

The Commission is aware of the claim that a few emotionally unstable or impulsive individuals have become particularly aggressive or impulsive under the influence of marihuana. As we have noted, some newspaper accounts have attributed sensational homicides or sexual assaults to marihuana-induced transitory psychotic states on the part of the user. No evidence exists, however, to indicate that marihuana was responsible for generating or creating excessive aggressiveness or impulsivity in individuals having no prior history of impulse or personality disorder. The most that can be said is that in those rare instances, marihuana may have aggravated a preexisting condition.

In sum, the weight of the evidence is that marihuana does not cause violent or aggressive behavior, if anything, marihuana generally serves to inhibit the expression of such behavior. Marihuana-induced relaxation of inhibitions is not ordinarily accompanied by an exaggeration of aggressive tendencies.

No evidence exists that marihuana use will cause or lead to the commission of violent or aggressive behavior by the large majority of psychologically and socially mature individuals in the general population.


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