A major systematic review led by King’s College London has established a significant association between cannabis use and an increased likelihood of engaging in violent behavior. The research, published in the journal Psychological Medicine, analyzed data from 63 studies involving more than 265,000 participants.
According to the findings, individuals in the general population who use cannabis are approximately twice as likely to commit violent acts compared to non-users. The risk profile is even steeper for those receiving psychiatric care; among this group, cannabis users were found to be two and a half times more likely to be violent than psychiatric patients who do not use the drug.
The study also examined the relationship between cannabis and victimization. People who used cannabis were about one and a half times more likely to become victims of violence themselves, with the analysis revealing that this association was stronger among women than men.
When focusing specifically on violence that resulted in criminal convictions, the disparity was even more pronounced. The researchers noted that cannabis users were three to four times as likely to have a criminal conviction related to violent acts.
Dr. Marta Di Forti, a co-author from the Institute of Psychiatry, Psychology & Neuroscience at King’s College London and South London and Maudsley NHS Foundation Trust, highlighted the clinical relevance of these findings. “As a clinician, I’ve seen how heavy cannabis use can be a factor in violence,” Di Forti said. “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.”
Professor Sir Robin Murray, the senior author of the study, emphasized the need to broaden the public discourse on cannabis risks. “As cannabis becomes more commercialized and legalized around the world, the conversation about its risks has focused mostly on the person using it,” Murray stated. “This review shows that violence, both committing it and experiencing it, needs to be part of that conversation too.”
The researchers utilized the World Health Organization’s broad definition of violence, which encompasses physical, sexual, and psychological aggression toward others, occurring both within and outside of intimate relationships. They differentiated between self-reported violent acts and those leading to criminal charges, prioritizing the most serious form of violence when individual studies reported multiple categories.
While the data shows a strong correlation, the authors stressed that the review identifies an association rather than proving that cannabis directly causes violence. The link persisted in longitudinal studies, although the effect size was smaller than in cross-sectional analyses. The researchers cautioned that cannabis use frequently coincides with other risk factors, such as alcohol consumption, use of other drugs, and adverse social circumstances, which may also contribute to violent behavior.
Based on these results, the authors recommend that mental health services routinely assess cannabis use when evaluating a patient’s risk of violence. They also call for public health communications to include information regarding the potential connection between cannabis and violent incidents.
The study acknowledged certain limitations, noting that few of the included studies measured the frequency or quantity of cannabis use. Additionally, most of the research was conducted prior to the widespread availability of high-potency cannabis products, leading researchers to suggest that daily use of modern, more potent strains could potentially be linked to even stronger effects.
The research was supported by the National Institute for Health and Care Research Biomedical Research Centre and the Medical Research Council.
With modern high-potency strains becoming common, I worry these figures might actually underestimate the current risk. We need updated data urgently.
I’m surprised by the stat about women being more likely to become victims. That’s a critical detail often lost in these broad summaries.
Correlation isn’t causation, though. Do violent people simply seek out cannabis, or does the drug cause the violence? The article admits the nuance.
This confirms what many clinicians have suspected for years. The link between heavy use and aggression is hard to ignore now.