Large-scale review links cannabis use to increased violence risk, both as perpetrators and victims

Comprehensive Analysis of Cannabis and Violence

Researchers at King's College London have conducted a sweeping meta-analysis of 63 studies encompassing more than 265,000 individuals, concluding that cannabis users face significantly elevated risks of both committing violent acts and becoming victims of violence themselves. The analysis, published in Psychological Medicine, represents one of the largest systematic reviews examining this relationship and provides what researchers describe as a more confident foundation for discussing cannabis-related violence risks.

The study separated analysis of the general population from those receiving psychiatric care, and employed the World Health Organization's expansive definition of violence—encompassing physical, sexual, and psychological harm in both intimate and non-intimate contexts. Researchers distinguished between self-reported violent incidents and those resulting in criminal convictions, focusing on the most severe form of violence when individual studies measured multiple types.

Key Findings on Violence Perpetration

The magnitude of increased risk varied depending on the population studied. In the general population, cannabis users were approximately twice as likely to commit violent acts compared to non-users. Among people receiving psychiatric care, the disparity widened considerably: cannabis users were roughly two and a half times more likely to engage in violent behavior than psychiatric patients who did not use cannabis. For violence severe enough to result in criminal conviction, the association intensified further, with cannabis users showing three to four times higher likelihood of conviction compared to non-users.

Interestingly, these associations appeared stronger in cross-sectional studies examining a single point in time compared to longitudinal research following individuals over extended periods, though temporal relationships remained significant. The researchers emphasized that these findings emerged from multiple studies examining the relationship across different populations and contexts, lending greater confidence to the overall pattern.

Victimization and Gender Differences

The review identified a second critical finding: cannabis users themselves experience elevated risk of becoming violence victims, with users approximately one and a half times more likely to experience violent acts than non-users. This victimization association demonstrated notable gender differences, proving substantially stronger among women than men—a distinction with potential public health and safety implications.

Dr. Marta Di Forti, co-author of the analysis, noted that while clinical experience has long suggested links between heavy cannabis use and violent behavior, the scale of this review permits more confident public statements about the risks while avoiding broad stigmatization of cannabis users generally.

Important Limitations and Caveats

The researchers exercised considerable caution in interpreting their findings, emphasizing that the review demonstrates association rather than causation. Cannabis use frequently co-occurs with numerous other risk factors for violence—including alcohol consumption, other substance use, and adverse social circumstances—any of which might independently contribute to violent behavior or victimization. The study cannot definitively isolate cannabis as the causal agent.

Methodological limitations constrain the conclusions further. Few included studies measured dosage or frequency of cannabis use, limiting understanding of dose-response relationships. Findings regarding criminal convictions rested on a comparatively limited number of studies. Critically, most research predates the emergence of highly potent cannabis products now common in legalized markets, raising questions about whether associations might be stronger or different with today's more concentrated formulations.

Public Health and Clinical Implications

Based on these findings, researchers recommend that mental health services routinely assess cannabis use when evaluating patients' violence risk. They further propose that public health communications about cannabis incorporate discussion of violence connections alongside other documented health risks. Senior author Professor Sir Robin Murray highlighted that as cannabis becomes increasingly commercialized and legalized worldwide, policy conversations have centered on individual users' health risks while largely ignoring the interpersonal violence dimension.

The timing of this analysis reflects significant shifts in cannabis regulation globally. As legalization expands access and normalization continues, understanding the full risk profile—particularly risks extending beyond individual users to those around them—gains urgency for clinicians, policymakers, and public health authorities.