Researchers at King’s College London pooled information from 63 studies into a review covering more than 265,000 individuals, and found that cannabis use was linked to higher rates of both committing violent acts and being a victim of them.
The Numbers Behind the Link
According to ScienceDaily’s review, individuals who used cannabis were roughly twice as likely to commit a violent act compared to those who did not use it. Among people receiving psychiatric care, cannabis users were about two and a half times as likely to be violent as patients who did not use the drug.
Violence against individuals followed a similar trend. People who used cannabis were roughly one and a half times more likely to be targeted by violent acts, and this connection was stronger for women than for men.
What the Review Looked At
The scientists relied on the World Health Organization’s wide-ranging definition of violence, which includes physical, sexual and psychological injury inflicted upon another person, whether within or beyond intimate relationships. They distinguished between incidents reported by participants themselves and those that led to criminal convictions.
The review centered on the most severe form of violence reported when individual studies measured multiple kinds. The results appeared in Psychological Medicine.
Why the Clinicians Cautiously Welcome the Results
Co-author Dr. Marta Di Forti said the review gives doctors a firmer basis for discussing the dangers involved, without casting shame on people who simply consume cannabis.
“As a clinician, I’ve seen how heavy cannabis use can be a factor in violence,” she 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.”
The Broader Context of the Review
The findings showed that individuals who used cannabis were between three and four times more likely to have received a conviction for violent offenses that resulted in a criminal record.
The senior author of the study, Professor Sir Robin Murray, says the discussion around the dangers of cannabis has mostly revolved around the individual taking it. He argues that violence should also enter that conversation.
“As cannabis becomes more commercialized and legalized around the world, the conversation about its risks has focused mostly on the person using it,” he said. “This review shows that violence, both committing it and experiencing it, needs to be part of that conversation too.”
What the Findings Mean for Practice
When assessing a person’s risk of violence, the researchers recommend that mental health services routinely inquire about cannabis use. They further contend that any public health messaging on cannabis should address the possible link to violence.
The Limits of the Evidence
The review points to a connection rather than proving that cannabis directly leads to violence. Cannabis consumption frequently happens alongside other things that can raise the risk of violent behavior or being harmed, such as drinking alcohol, using other drugs, and hard social conditions.
A relatively small number of the studies looked at how much cannabis people used or how often they used it. Similarly, the findings involving criminal convictions came from a relatively limited number of studies.
The bulk of the study took place prior to high-potency cannabis becoming widespread. So the investigators propose that current heavy users of much stronger products might experience more pronounced effects than those observed in earlier research.
Funding and Disclosure
The research received funding from the NIHR Biomedical Research Centre at the Maudsley and the Medical Research Council (MR/T007818/1). Any opinions stated are those of the researchers alone and do not represent the views of the NIHR or the Department of Health and Social Care.
Key Facts at a Glance
- More than 265,000 people across 63 studies were included.
- Cannabis users were roughly twice as likely to commit violent acts.
- Women showed a stronger link to victimization than men.
- Criminal conviction cases showed a three to four times higher risk.
- The review was published in Psychological Medicine.
The review raises real concern without settling blame.
Source material: “Cannabis users were twice as likely to commit violence, review finds,” ScienceDaily.
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