Cannabis Use Tied to Double the Odds of Violence, Massive Study Finds

Cannabis has a reputation for mellowing people out, not winding them up. A sweeping new analysis complicates that picture. People who use cannabis have about twice the odds of committing a violent act as those who don’t, according to one of the largest reviews of its kind, drawing on data from more than 265,000 people. In studies that measured violence through criminal convictions, cannabis users had close to four times the odds of non-users.

Marijuana has been moving toward mainstream acceptance for years. Twenty-four U.S. states plus the District of Columbia now allow recreational use, and countries from Canada to Germany have opened the door to legal sales. Most of the public conversation around cannabis centers on its effects on the user: memory problems, addiction risk, links to psychosis. Far less attention has gone to a harder question, whether cannabis use might make someone more likely to hurt another person, or become a victim themselves.

A team of researchers based at King’s College London decided to dig into that gap. They combed through decades of scientific literature and pulled together 63 separate studies covering more than a quarter million people, then crunched the numbers to see what the overall pattern looked like. Writing in the journal Psychological Medicine, they reported a consistent, sizable link between cannabis use and violence, one that held up across different countries, age groups, and study designs.

How Researchers Linked Cannabis Use to Violence

Rather than running a new experiment, the team conducted what’s called a meta-analysis, gathering every relevant study they could find and combining the results into one big picture. They searched three major medical research databases for studies published up through November 2024, screened more than 7,500 records, and eventually narrowed things down to 63 studies that measured cannabis use and some form of violence, either as a perpetrator or as a victim.

Those studies covered nearly 209,000 people tracked for whether cannabis use predicted them committing violence, and another roughly 86,500 people tracked for whether cannabis use predicted them becoming a victim. Most participants came from the general population, though thirteen of the studies focused specifically on psychiatric patients. The violence measured ranged from fighting and assault to sexual aggression and robbery, and some studies relied on people self-reporting their own behavior while others used official criminal records.

Because the studies varied so much in design, some following people over years and others taking a single snapshot in time, the researchers ran the numbers separately for each type and also broke results down by gender, by population (general versus psychiatric), and by how severe the violence was.

Breaking Down the Cannabis-Violence Numbers

Among the general population, cannabis users showed much higher odds of committing a violent act than non-users. That risk showed up in both long-term tracking studies and one-time surveys, though it was stronger in the snapshot studies. When the researchers zoomed in on studies that measured violence through criminal conviction records rather than self-reports, the link got much stronger in both the general population and psychiatric patients.

That pattern held up, and even intensified, among people with serious mental illness. Cannabis-using psychiatric patients showed higher odds of committing violence than cannabis-using members of the general population, a finding that echoes earlier research on the topic.

Gender differences showed up too. Among people who committed violence, the link to cannabis use was somewhat stronger in females than in males. On the flip side, cannabis use was also tied to a higher risk of being a victim of violence, and here again, the risk was more pronounced in females and in mixed-gender groups than in men alone. The setting mattered as well: the link was weaker for violence between intimate partners or dates, and stronger in other kinds of violent encounters.

Researchers also checked whether their results could be explained away by lower-quality studies or by which studies got published in the first place. After running statistical checks for publication bias and re-running the analysis while excluding weaker studies, the core findings held steady. Results that accounted for other factors came out broadly similar to those that didn’t, though the researchers were careful to note that influences they couldn’t fully rule out might still help explain the link.

Why Cannabis Use Might Lead to Violence

Researchers stopped short of claiming cannabis directly causes people to become violent. Instead, they laid out several possible explanations that likely work together. Heavy cannabis use can impair attention, decision-making, and impulse control. It can also affect mood, sometimes fueling irritability or anger, especially during withdrawal. Regular use has also been tied to increased paranoia, which could lead someone to misread a neutral situation as threatening and react defensively.

There’s also the matter of who tends to use cannabis in the first place. People with higher impulsivity or antisocial tendencies may be more likely both to use cannabis and to engage in risky or violent behavior, meaning cannabis use and violence might sometimes be two symptoms of the same underlying pattern rather than one directly causing the other. The researchers note that the relationship likely involves several overlapping factors rather than one simple cause-and-effect chain.

As for the victimization findings, the authors pointed to increased vulnerability rather than direct cause and effect. Cannabis users may spend more time in risky situations or around peers involved in substance use, which could raise their exposure to violent situations without cannabis itself being the direct trigger.

What the Cannabis-Violence Findings Mean Going Forward

This analysis does not prove that smoking or eating cannabis flips a switch that makes someone violent. What it does show is a pattern too large and too consistent to dismiss, one that shows up across dozens of studies, different countries, and different ways of measuring both cannabis use and violence. As more places move to legalize and commercialize marijuana, this research is a reminder that public health conversations about cannabis need to account for its effects on the people around the user, not only the user. For psychiatric patients in particular, the findings make a case for treating cannabis use as a routine part of assessing violence risk, not an afterthought.

Disclaimer: This article summarizes a systematic review and meta-analysis of observational studies. Such research can identify associations between cannabis use and violence but cannot establish that cannabis use directly causes violent behavior. Most included studies were cross-sectional, and the researchers noted that factors they could not fully measure, such as alcohol or other drug use, may contribute to the link.

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