A comprehensive review led by researchers at King's College London indicates that cannabis users are at a higher risk of committing violent acts as well as experiencing violence themselves. The researchers from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) analyzed data from 63 studies that involved over 265,000 participants, distinguishing between the general population and those receiving psychiatric care.
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The review utilized the World Health Organization's broad definition of violence, which encompasses physical, sexual, and psychological violence within both intimate and non-intimate relationships. It differentiated between self-reported violent incidents and those leading to criminal convictions, focusing on the most serious reported forms of violence. The findings were published in the journal Psychological Medicine.
Dr. Marta Di Forti, a co-author from IoPPN, commented on the findings, acknowledging both the connection between heavy cannabis use and violence while cautioning against stigmatizing cannabis users more broadly.
In addition to violence perpetration, the review found that cannabis users were about 1.5 times more likely to be victims of violence, with this risk appearing more pronounced among women. Professor Sir Robin Murray, senior author of the study, noted that in the general population, individuals who used cannabis were approximately twice as likely to have committed a violent act compared to non-users. Among psychiatric patients, cannabis users were found to be about 2.5 times more likely to exhibit violent behavior. The review highlighted that those who used cannabis were three to four times more likely to receive a criminal conviction for violent acts.
The researchers suggest that as cannabis becomes more legalized and commercialized, conversations about its risks must include the potential for violence, both in committing and experiencing it. They recommend that mental health services routinely inquire about cannabis use in violence risk assessments and that public health information discusses the possible links between cannabis and violence.
However, it is important to note that this review identifies an association rather than proving causation. Cannabis use often coincides with other risk factors for violence, such as alcohol use and adverse social circumstances. The study also acknowledged limitations, including the small number of studies that quantified cannabis use, and indicated that most research predates the rise of high-potency cannabis, which may have stronger implications for violence risk. The study was supported by the National Institute for Health and Care Research (NIHR) and the Medical Research Council.