Cannabis doesn't make you violent—despite what recent reports have claimed
In what looked like a return to the dark days of "Reefer Madness"—a 1936 film that portrayed cannabis as a drug that could drive people to madness and murder—a recent article in the Daily Telegraph claimed that cannabis users are "twice as likely to be violent."
A recent article claimed that cannabis users are twice as likely to be violent, based on a review of 63 studies. However, this headline overstated the findings. The review itself found that cannabis users had 17% higher odds of violence than non-users, not twice the likelihood. This discrepancy arises because "odds" and "likelihood" are not the same thing.
The researchers attempted to account for confounding factors such as poverty, alcohol, other drugs, and difficult upbringings that could explain the link between cannabis use and violence. They also noted that the review's findings were based on mostly cross-sectional studies, which measure variables at a single point in time and may not establish causation.
Longitudinal studies, which follow participants over time, showed a weaker link between cannabis use and violence. The review contained several limitations, including the difficulty in determining what constitutes cannabis use and violence, as well as potential bias in study design and data collection. The review's authors acknowledged these limitations and rated the certainty of their evidence as very low.
Despite these concerns, the headline figure in the original report gave the impression that the evidence was much stronger than it actually was.
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