September 29, 2026

expert reaction to systematic review and meta-analysis of cannabis use and violence

Scientist comments on a systematic review and meta-analysis, published in Psychological Medicine, investigating cannabis use and violence. 

Prof Simon Moore, Professor of Public Health Research and Director of the Violence Research Group at Cardiff University, said:

“This meta-analysis suggests that cannabis users have about twice the odds of committing violence. However, it did not look at where, with whom or in what circumstances cannabis was used, and the main text does not say whether the original studies allowed for peer group, neighbourhood or exposure to violent environments. Results with and without adjustment were similar (OR 2.01 and 2.19), but this only shows that the factors adjusted for made little difference, not that context was taken into account. Studies that followed people over time found a much smaller association (OR 1.17), which suggests that some of the larger association seen in cross-sectional studies may reflect circumstances that were not measured. The gap between the two designs is close to twofold for both perpetration and victimisation, roughly the same size as the headline effect itself, and a confounder no stronger than commonly cited factors such as peer group or neighbourhood would be enough to account for the longitudinal estimate entirely. Without this information, the review cannot say whether cannabis itself or the environments in which it is used explain the violence. Because cannabis remains illegal in most jurisdictions, and illegal markets bring users into contact with people and places where violence is more likely, this omission is notable.”

‘Cannabis use is associated with increased risk of violence: A systematic review and meta-analysis’ by Giulia Trotta et al. is published in Psychological Medicine

DOI: 10.1017/S0033291726105856

Declared interests

Prof Simon Moore: Simon has no interests or conflicts to declare.