A comprehensive and far-reaching review led by researchers at King’s College London has uncovered a significant association between cannabis use and violence, revealing that individuals who use the drug are notably more likely to both perpetrate violent acts and become victims of violence themselves. The study, which represents one of the most extensive syntheses of data on this subject to date, suggests that the relationship between cannabis and aggression is more complex and pervasive than previously understood, affecting both the general population and those already receiving specialized mental health care.
The research was spearheaded by the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s College London. To reach their conclusions, the research team conducted a meta-analysis that combined data from 63 individual studies, spanning a diverse range of demographics and geographic locations. In total, the review analyzed the experiences and behaviors of more than 265,000 people, providing a robust statistical foundation for the findings. By synthesizing decades of research, the team sought to provide a clearer picture of the risks associated with cannabis, a substance that is seeing a global trend toward decriminalization, legalization, and commercialization.
What the Review Examined
In designing the study, the researchers adopted a rigorous and inclusive methodology to ensure the findings captured the full spectrum of violent behavior. They utilized the World Health Organization’s (WHO) broad definition of violence. This definition is not limited to physical battery but encompasses a wide array of harmful behaviors, including sexual violence and psychological aggression. The scope of the review covered acts committed against others both within the home—such as intimate partner violence—and in the broader community.
A key strength of this review was its effort to distinguish between different types of evidence. The researchers carefully separated instances of self-reported violence from cases that resulted in formal criminal convictions. This distinction is crucial for understanding the gap between everyday aggressive behavior and the type of violence that intersects with the legal system. Furthermore, when individual studies measured multiple forms of violence, the King’s College team prioritized the most serious type reported, ensuring that the gravity of the outcomes was accurately reflected in their final analysis. The comprehensive findings of this review have been published in the prestigious journal Psychological Medicine.
Dr. Marta Di Forti, a co-author of the study and a prominent figure at the IoPPN as well as the South London and Maudsley NHS Foundation Trust, highlighted the clinical significance of these findings. Dr. Di Forti noted that while frontline healthcare workers have long observed these patterns, the scientific community has historically been hesitant to draw firm conclusions without the backing of a large-scale data set.
"As a clinician, I’ve seen how heavy cannabis use can be a factor in violence," Dr. Di Forti explained. "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." Her comments underscore a growing consensus that the public needs a more nuanced understanding of the drug’s potential side effects, moving beyond the binary of "harmless" versus "dangerous."
Cannabis Use and Victimization
