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Cannabis and Aggression

Cannabis is widely regarded as a "peace" inducing drug, a legacy of the hippie era in the 1960s. Relaxation and stress relief are among the most commonly reported reasons for use of the drug, and IDMU surveys have found "reduced aggression" to be a commonly-perceived "benefit" of using the drug. Several synthetic cannabinoids have been investigated as sedative/relaxants. Studies of cannabis and driving have identified a reduction in aggressive driving or risky manoevres as an explanation for the relatively low level of impairment, or even beneficial effects, on driving performance. However, firm evidence of reduced aggression in humans is limited.

In a study of urine toxicology following psychiatric emergency admissions, Dhossche reported "Various indices of substance abuse, including... cannabis, were not associated with aggressive behavior." In a study of offenders referred to a South African psychiatric unit, Hemphill et al concluded "(cannabis) appeared to diminish the action of alcohol, and may inhibit urges toward violence and rape in aggressive persons and psychopaths." In Egypt, Souief reported "Compared with controls, cannabis takers were... low on quarrelsomeness and high on selflessness"

In mice, cannabinoids appear to reduce "attack" behaviour, increase submissive behaviour, the "flight" response to aggression. "Intruder males" treated with hashish "were more frequently attacked and submission and flight was increased". Ham et al found "THC produced a dose dependent depression of aggression in isolated mice" while Cutler et al also found a rebound effect, with dominant males showing an increase in aggression one week following withdrawal of cannabis. In rats, THC (but not CBD) was found to reduce aggressive responses and increase avoidance behaviour in male-male encounters, as well as to reduce predatory aggression.

In baboons, Sieber reported "In the "approaching" male the drug reduced "approach" and the aggressive elements "hit-ground", "brows-back" and "attack" but increased the frequency of "retreat". Social interactions were generally diminished. In the "retreating" male friendly social interactions as "lipsmack" and "touch-back/handle-genitals" were suppressed but the threatening elements "open-mouth" and "tooth-grind" were stimulated. "Retreat" was additionally more frequent.", However Lewett et al reported that baboon responses varied considerably between individual animals, and Sassenrath et al, working with monkeys, found a biphasic reponse with increased aggressive responses following development of tolerance to the drug effects.

However some researchers have reported increased "aggressive" responses on human or animal behavioural models, Carlini et al reported increased aggressive behaviour in THC-dosed rats following deprivation of REM sleep, or after developing tolerance to morphine. Dorr et al reported that a high THC dose (2.5 mg/kg) "markedly increased the percentage of animals which showed both aggression and flight acts--a rare combination among controls." Clinicians have reported a toxic psychosis following prolonged or heavy cannabis use, including aggressive behaviour or panic disorder, however the existence of a specific "cannabis psychosis" is not firmly established in the absence of an underlying psychopathology.

Drugs used to treat aggression and violence have included antipsychotic drugs (major tranquilliers such as chlorpromazine), minor tranquillisers (benzodiazepines), lithium, anticonvulsants, and hormonal therapies. All of the above therapies involve risks, including extrapyramidal symptoms (uncontrolled movements) from phenothiazines, and severe dependence from benzodiazepines.

While the effects of cannabis on aggression in humans have not been adequately studied, there is evidence from animal studies that cannabis (THC) can reduce aggressive behaviour in response to challenge, rendering the subject more likely to avoid an aggressive incident or aggressive responses to a threat. However, for some individuals heavy use of cannabis may precipitate a psychotic reaction with aggressive outbursts. These incidents are relatively rare, and highlight the varied individual responses to the drug. The preponderance of scientific evidence does suggest cannabis may have a role in reducing aggressive behaviour, and the drug is certainly perceived to do so by a large number of cannabis users.

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