Cannabis Use Tied to Greater Risk of Violence, Review

Think of public health as concentric circles. What affects the person in the center ripples outward to partners, families, and communities. A sweeping analysis now suggests that cannabis use is associated not only with harms to individual users but also with higher odds of violence in both directions: committing it and becoming a victim.

What the review examined and why it matters

Researchers at King’s College London pooled evidence from 63 studies covering more than 265,000 people to map connections between cannabis use and violent behavior. The findings, published in Psychological Medicine, show consistently higher rates of violent acts among people who used cannabis compared with non-users. The signal appeared in the general population and was even stronger among people receiving psychiatric care.

Numbers tell a blunt story. In community samples, cannabis users were roughly twice as likely to have committed a violent act as non-users. Among psychiatric patients, the odds rose to about two and a half times. For violent acts that led to criminal convictions, the association climbed further — studies suggested three to four times greater likelihood for those who used cannabis.

These patterns were observed across different study designs. Longitudinal studies that followed people over time still found an association, though the effect sizes tended to be smaller than those seen in cross-sectional snapshots. That consistency across methods strengthens the case that the link is not an artifact of one study type, even if it stops short of proving causation.

Different measures, same direction

The team intentionally separated groups and measurement types to check robustness. They analyzed general population samples separately from people in psychiatric services, and they contrasted self-reported violence with events recorded as criminal convictions. Violence was defined broadly using World Health Organization criteria, spanning physical, sexual, and psychological harm, whether inside relationships or in public.

When a study reported multiple forms of aggression, reviewers used the most serious form to avoid diluting the signal. That conservative choice helped ensure the association was not driven by minor or ambiguous incidents. Importantly, cannabis users were not only more likely to perpetrate violence; they were also more likely to experience it. Victimization odds were about 1.5 times higher for people who used cannabis, with the effect appearing stronger among women than men.

Professor Sir Robin Murray, who led the review team at the Institute of Psychiatry, Psychology & Neuroscience, noted that the conversation around cannabis risk has largely focused on the user. He argued that these findings make clear that any public-health discussion should also account for violence as a potential downstream concern, affecting people beyond the user alone.

Why this does not prove cannabis causes violence

Association is not causation. Cannabis use often co-occurs with other factors that elevate violence risk: alcohol and other substance use, socioeconomic stress, exposure to violent environments, and untreated mental-health problems. Those overlapping drivers complicate efforts to isolate cannabis as the causal agent.

Another key limitation: many studies did not measure dose or frequency with precision. How much cannabis someone used, how often, and whether products were high in THC were often unknown. Most of the included research predates the widespread availability of today's high-potency cannabis products. The authors caution that daily use of stronger formulations could have larger effects, but current data cannot confirm that.

Estimates based on criminal convictions came from fewer studies, and conviction data can reflect policing patterns and social inequities as much as individual behavior. In short, the evidence supports a reliable association but leaves open the question of how much cannabis itself contributes versus the social and clinical contexts in which use occurs.

Implications for clinical practice and public messaging

Given the association across diverse settings, the authors recommend that mental-health services routinely inquire about cannabis use when assessing someone’s risk of violence. That is a pragmatic step: identifying substance use is actionable in clinical settings and can shape risk management and treatment plans.

Public-health campaigns and policy debates about legalization and commercialization should also factor in these findings. If cannabis markets expand without attention to potential harms beyond the user, communities may face unanticipated social costs. Messaging that highlights safety, recognizes the role of poly-substance use, and directs people to support services is one practical response.

Expert Insight

Dr. Lena Carter, a forensic psychiatrist unaffiliated with the study, commented: "This review compels clinicians and policymakers to broaden their view. We cannot treat substance use in isolation. When cannabis use appears alongside other risks, the combined effect can raise the likelihood of harm to others as well as to the user. Screening and integrated care make a measurable difference."

Her point underscores a familiar public-health principle: interventions that address multiple, interacting risks tend to work better than single-issue approaches.

Conclusion

The King’s College-led review does not settle the question of cause, but it does change the terms of the debate. Cannabis use is associated with higher odds of both committing and experiencing violence across large and varied samples. This finding calls for more nuanced clinical protocols, informed public-health messaging, and fresh research that measures dose, potency, and context. Policymakers and clinicians should treat violence as a real dimension of cannabis-related harm, even as scientists continue to untangle the mechanisms behind the association.