As cannabis becomes more commercialized and legalized around the world, discussion of its risks has largely focused on what happens to the person using it. However, a large new review adds another dimension, because any connection to violence could affect not only cannabis users themselves but also the people around them.
A comprehensive review led by researchers at King’s College London found that people who used cannabis were more likely both to commit violent acts and to experience violence themselves. The analysis brought together 63 studies involving more than 265,000 people, making it one of the most extensive examinations of the relationship to date. The findings were published in the peer-reviewed journal Psychological Medicine.
Violence Rises Across Both General Population and Psychiatric Care
The researchers analyzed the general population separately from people receiving psychiatric care because the relationship between cannabis use and violence could differ between those groups. 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.
Furthermore, the link held in longitudinal studies that followed people over time, though it was smaller than in cross-sectional 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,” said Professor Sir Robin Murray, senior author of the study from the Institute of Psychiatry, Psychology & Neuroscience at King’s College London.
Different Measures Point the Same Way
The team distinguished violence reported by participants themselves from acts that resulted in criminal convictions. They defined violence broadly using the World Health Organization’s criteria, which include physical, sexual, and psychological violence against another person, whether it occurs within a relationship or outside one. When an individual study measured several forms of violence, the researchers used the most serious form reported. That approach allowed them to examine whether the association appeared across different definitions and settings rather than depending on a single measure.
Cannabis Users Also Faced More Violence
The relationship was not limited to perpetration. Cannabis users were also about one and a half times as likely to become victims of violence. Moreover, the association with victimization was stronger among women than among men.
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, said the scale of the evidence allowed researchers to characterize the relationship more confidently without treating cannabis use as proof that someone will become violent.
“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,” Di Forti said.
Analysis: What This Means for Public Health and Risk Assessment
1. Association is consistent, but not causation: The review found a consistent link across 63 studies, including longitudinal designs. However, it cannot prove cannabis itself causes violence.
2. Co-occurring factors matter: Cannabis use often occurs alongside alcohol and other drug use, as well as difficult social conditions, making it difficult to isolate cannabis-specific effects.
3. Clinical implication: The researchers say results support routinely asking about cannabis use when mental health services assess a person’s risk of violence.
4. Public health messaging gap: Authors argue that the possibility of violence, both committing and experiencing it, should be included in public health messaging about cannabis as legalization expands.
5. Potency question remains unanswered: Most included research was conducted before high-potency cannabis became widespread. The researchers suggest daily use of today’s more potent forms may produce greater effects, but the reviewed studies could not establish that.
The Evidence Cannot Establish Causation – Key Limitations
Although the association appeared across multiple kinds of studies, the evidence cannot establish that cannabis itself causes violence. Several limitations affect interpretation.
First, few studies measured how much cannabis people used or how often they used it, so dose-response relationships remain unclear. Second, estimates involving criminal convictions came from a relatively small number of studies. Third, most research predates the current era of high-potency products.
Therefore, experts caution against stigmatizing all cannabis users or assuming individual risk from population-level data.
Q&A
Q: How many people were included in the cannabis and violence review?
A: The review analyzed 63 studies involving more than 265,000 people, led by King’s College London and published in Psychological Medicine.
Q: How much more likely were cannabis users to commit violence?
A: In the general population, cannabis users were about twice as likely to have committed violence. In psychiatric care, they were about 2.5 times as likely. For convictions, the risk was 3 to 4 times higher.
Q: Were cannabis users also more likely to be victims of violence?
A: Yes, cannabis users were about 1.5 times as likely to experience violence themselves, with a stronger association observed among women.
Q: Does cannabis cause violence?
A: No, the review found an association, not causation. Co-occurring factors like alcohol, other drugs, and social conditions make it difficult to attribute risk specifically to cannabis.
FAQ
1. What definition of violence did researchers use?
They used WHO criteria including physical, sexual, and psychological violence against another person, inside or outside relationships, using the most serious form reported in each study.
2. Did the study look at different potency or frequency of use?
Few studies measured amount or frequency, and most were done before high-potency cannabis became common, so potency effects could not be established.
3. What do experts recommend for mental health services?
Authors recommend routinely asking about cannabis use during violence risk assessments in mental health settings.
4. Does this mean all cannabis users become violent?
No. The review reports increased likelihood at the population level. Dr. Di Forti emphasized caution not to stigmatize people who use cannabis broadly.
5. Where was the study published?
In Psychological Medicine, a peer-reviewed journal, by researchers from the Institute of Psychiatry, Psychology & Neuroscience at King’s College London.
Disclaimer; This article is for general news and educational purposes only.
