New research from the United Kingdom has identified a significant association between cannabis use and violent behaviour, suggesting that people who use the drug may face higher risks of both committing and experiencing violence.
The findings come from a comprehensive review of 63 previous studies involving roughly 250,000 people.
Researchers examined evidence from the general population as well as people receiving psychiatric treatment to assess whether cannabis consumption was associated with interpersonal violence.
The review found that cannabis users in the general population were about twice as likely to engage in violent behavior as people who did not use the drug. Among psychiatric patients, the likelihood was approximately 2.5 times higher.
The association appeared even stronger when researchers focused specifically on violence resulting in a criminal conviction. In the general population, cannabis use was linked to a 3.75-fold increase in the risk of such violence.
The study also found that cannabis users were approximately 50% more likely to become victims of violence.
“The findings of our study underscore the importance of addressing this issue at both a societal and clinical level,” the researchers wrote in their paper, published in the journal Psychological Medicine.
However, the researchers stressed that their findings do not establish that cannabis directly causes people to become violent.
Marta Di Forti, a professor of drug use, genetics and psychosis at King’s College London and an author of the study, said clinical experience had already highlighted concerns about heavy cannabis consumption and violence.
“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,” said study author Marta Di Forti, a professor of drug use, genetics and psychosis at Kings College London, in a statement from the university.
Why cannabis may be associated with violence
The researchers point to several possible explanations for the relationship. Cannabis can affect cognitive abilities such as attention, decision-making, impulse control and problem-solving. Heavy, prolonged consumption may also interfere with emotional regulation, including the ability to manage anger.
Paranoia and other changes in perception may also occur more frequently among regular cannabis users, potentially contributing to situations in which conflict or violence becomes more likely.
But the researchers caution that cannabis may not be acting independently. Regular users may already be more likely to display impulsive behavior or participate in other risky activities. This could partly explain why they experience or perpetrate violence at higher rates.
The increased likelihood of being a victim of violence could similarly reflect differences in lifestyle or circumstances. Cannabis users may, for example, spend more time in environments where exposure to violent situations is already elevated.
The authors therefore argue that the relationship is likely to involve several overlapping factors rather than one straightforward biological pathway.
“The association between cannabis use and violence is likely to reflect multiple interacting pathways rather than a single direct causal mechanism.”
Risk may be greater with heavy use
Previous research has identified potential links between cannabis and violence in particular groups, including young people and individuals with serious mental health disorders. The new review suggests that an association may also exist among cannabis users more broadly.
At the same time, the researchers noted important limitations in the available evidence. The studies included in the review differed in design, population and methodology, meaning the strength of the relationship varied.
Research that tracked participants over time generally identified a weaker association than studies that assessed people at a single point. This difference further underscores why the findings should not be interpreted as proof that cannabis use directly produces violent behavior.
Another concern is that many of the studies reviewed were conducted before the widespread availability of modern cannabis products containing substantially higher concentrations of THC. If stronger cannabis products carry greater risks, the researchers said, older studies may not fully capture the potential dangers associated with today’s products.
The findings do not mean that cannabis users are generally violent. Millions of people consume cannabis without committing violent acts or harming themselves or others. The researchers also emphasized that potential harms tend to be more pronounced among people who use cannabis heavily and persistently.
Rather than portraying cannabis as an automatic trigger for violence, the researchers say their findings support treating cannabis use as one potentially changeable factor among several that can contribute to violent behavior.
“From a public health perspective, violence should be considered alongside other established cannabis-related harms when developing prevention strategies, public education campaigns, and regulatory policies, particularly in jurisdictions where cannabis has been legalized or decriminalized,” they wrote.
