Cannabis Users Are More Likely to Commit Violence and Become Victims of It, Major Review Finds

People who use cannabis appear significantly more likely to both commit violence and become victims of it, according to a major review led by researchers at King’s College London. The analysis pooled data from 63 studies involving more than 265,000 participants worldwide.

Researchers from the Institute of Psychiatry, Psychology & Neuroscience examined data from the general population separately from people receiving psychiatric care. Their findings, published in Psychological Medicine, are among the most comprehensive analyses yet of the relationship between cannabis use and violence.

How researchers defined and measured violence

The review used the World Health Organization’s broad definition of violence, covering physical, sexual and psychological harm toward others, both within and outside intimate relationships. Researchers distinguished between self-reported violent behavior and incidents that resulted in criminal convictions.

When individual studies assessed multiple forms of violence, the authors focused on the most severe form recorded. This approach allowed them to compare findings across substantially different research designs and populations more consistently.

Higher risk of committing and experiencing violence

In the general population, people who used cannabis were about twice as likely to have committed a violent act as non-users. Among psychiatric patients, cannabis users were around two and a half times more likely to be violent than patients who did not use the drug.

The association persisted in studies that followed participants over time, although it was weaker than in studies capturing only a single point in time. When researchers examined violent acts resulting in criminal convictions, cannabis users were three to four times more likely to have been convicted.

The review also found that cannabis use was associated with a greater likelihood of experiencing violence. Users were roughly one and a half times more likely to become victims, with the association stronger among women than among men.

Clinical and public health implications

The authors say the findings should encourage mental health services to routinely ask about cannabis use when assessing a person’s risk of violent behavior or victimization. They also argue that cannabis-related public health campaigns should address potential links with violence alongside personal health effects.

Clinicians involved in the research report seeing heavy cannabis use as one factor among several in some violent incidents, particularly among patients already vulnerable because of mental illness. They stress, however, that most cannabis users are not violent and that the purpose of highlighting the association is risk awareness rather than stigma.

Association, not clear causation

Researchers emphasize that the review identifies an association and does not demonstrate that cannabis directly causes violence. Cannabis use frequently occurs alongside other risk factors, including alcohol use, other drugs, poverty, trauma and unstable living conditions.

Only a minority of the studies included in the review measured how frequently participants used cannabis or the potency of the products they consumed. This makes it difficult to determine whether heavy daily use or stronger cannabis products carry a distinctly greater risk.

Changing cannabis market and future research

Most of the studies included in the review were conducted before high-potency cannabis products became widespread across legal and illegal markets. Previous research has linked stronger cannabis products with higher risks of psychosis and dependency, raising questions about their possible relationship with violence.

The authors call for newer and more detailed research tracking frequency of cannabis use, product potency and the simultaneous use of other substances. They say clearer evidence could help inform regulations, clinical guidelines and public information campaigns in countries moving toward legalization or expanding commercial cannabis sales.

The study was supported by the National Institute for Health and Care Research Biomedical Research Centre at Maudsley and the UK Medical Research Council. The authors note that the views expressed are their own and do not necessarily represent those of the funding organizations or the Department of Health and Social Care.

Article prepared by Victoria Caldwell.