A comprehensive review by researchers at King’s College London shows that cannabis users face a higher likelihood of both committing violent acts and experiencing violence as victims.
The team from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) pooled data from 63 studies covering over 265,000 participants, examining the general population and psychiatric patients separately.
What the Review Examined
They adopted the WHO’s expansive definition of violence, encompassing physical, sexual and psychological aggression toward others, regardless of relationship context.
The investigators distinguished self‑reported incidents from official convictions and, where studies covered multiple violence types, concentrated on the most severe form observed. The results appear in Psychological Medicine.
Dr. Marta Di Forti, co‑author of the study from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s College London and South London and Maudsley NHS Foundation Trust, said:
“As a clinician, I’ve seen how heavy cannabis use can be a factor in violence. We’ve been cautious for a long time about how far we could go in describing this link, but a review of this size lets us speak with more confidence about the risks, while being careful not to stigmatize people who use cannabis more broadly.”
Cannabis Use and Victimization
The analysis also revealed that cannabis users were about one‑and‑a‑half times more likely to become victims of violence, with the association being stronger in women than in men.
Professor Sir Robin Murray, senior author of the study from the Institute of Psychiatry, Psychology & Neuroscience at King’s College London, said:
“In the general population, people who used cannabis were around twice as likely to have committed a violent act as those who didn’t; for those in psychiatric care, cannabis users were around two and a half times as likely to be violent as other psychiatric patients who didn’t use cannabis. The link held in studies that followed people over time, though it was smaller than in studies that looked at a single point in time. For violence that led to a criminal conviction, people who used cannabis were three to four times as likely to have been convicted.
“As cannabis becomes more commercialized and legalized around the world, the conversation about its risks has focused mostly on the person using it. This review shows that violence, both committing it and experiencing it, needs to be part of that conversation too.”
Implications for Mental Health and Public Health
Based on these findings, the authors recommend that mental‑health practitioners routinely screen for cannabis use when assessing violence risk and that public‑health messages address the potential link to violent behavior.
However, the researchers stress that the review identifies an association and does not prove that cannabis directly causes violence. Cannabis use often occurs alongside other factors that can also increase the risk of violent behavior or victimization, including alcohol use, other drug use and difficult social circumstances.
Important Limitations
Only a small number of the studies measured how much cannabis people used or how often they used it. The findings involving criminal convictions were also based on a relatively limited number of studies.
Most of the research was conducted before high‑potency cannabis became common. The researchers suggest that daily use of today’s more potent cannabis products could potentially be associated with stronger effects.
The study was supported by the National Institute for Health and Care Research (NIHR) Biomedical Research Centre: Maudsley and the Medical Research Council (MR/T007818/1). The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care.
