A large-scale, exhaustive review led by researchers at King’s College London has concluded that individuals who use cannabis are significantly more likely both to commit violent acts and to experience violence themselves. The landmark study, which aggregates data from dozens of independent research projects across multiple decades, sheds new light on the complex social and behavioral risks associated with cannabis consumption at a time when global attitudes, commercialization, and legal frameworks surrounding the drug are rapidly shifting.
Researchers from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s College London systematically combined and analyzed data drawn from 63 distinct studies, encompassing a massive participant pool of more than 265,000 individuals. To ensure a nuanced understanding of the data, the research team analyzed the general population completely separately from individuals who were receiving active psychiatric care, allowing for clearer insights into how underlying mental health conditions might intersect with substance use and behavioral outcomes.
What the Review Examined
In executing this comprehensive review, the research team adopted the World Health Organization’s broad and comprehensive definition of violence. This inclusive framework encompasses physical, sexual, and psychological violence directed toward another person, capturing incidents that occur both inside and outside of intimate relationships. By casting a wide net, the investigators sought to capture the full spectrum of aggressive interactions rather than focusing solely on isolated definitions of physical assault.
Furthermore, the methodology distinguished carefully between self-reported violence and documented cases that culminated in formal criminal convictions. When individual studies measured multiple forms of violence simultaneously, the researchers deliberately focused on the most serious type reported to maintain analytical consistency. The complete findings of this extensive investigation have been published in the peer-reviewed journal Psychological Medicine.
Dr. Marta Di Forti, a co-author of the study from the IoPPN at King’s College London and the South London and Maudsley NHS Foundation Trust, reflected on the clinical significance of the findings from her perspective as a practicing physician. "As a clinician, I’ve seen how heavy cannabis use can be a factor in violence," Dr. Di Forti noted. "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."
Cannabis Use and Victimization
Beyond the well-documented examination of violent behavior perpetrated by users, the review uncovered a troubling parallel concerning victimization. The data revealed that individuals who consumed cannabis were approximately one and a half times as likely to become victims of violence compared to non-users. Interestingly, this association between cannabis use and personal victimization proved to be notably stronger among women than among men, pointing to potential gender-specific vulnerabilities that warrant further targeted investigation by public health experts.
Professor Sir Robin Murray, senior author of the study from the IoPPN at King’s College London, elaborated on the quantitative scale of the findings across different demographics and institutional settings. "In the general population, people who used cannabis were around twice as likely to have committed a violent act as those who didn’t; for those in psychiatric care, cannabis users were around two and a half times as likely to be violent as other psychiatric patients who didn’t use cannabis," Professor Murray explained.
He further highlighted the longitudinal consistency and the severe end of the legal spectrum identified in the data. "The link held in studies that followed people over time, though it was smaller than in studies that looked at a single point in time. For violence that led to a criminal conviction, people who used cannabis were three to four times as likely to have been convicted," he said.
As governments around the world continue to grapple with shifting legal landscapes, Professor Murray emphasized the timely nature and broader implications of the research. "As cannabis becomes more commercialized and legalized around the world, the conversation about its risks has focused mostly on the person using it. This review shows that violence, both committing it and experiencing it, needs to be part of that conversation too."
Implications for Mental Health and Public Health
In light of these findings, the research team argues that current healthcare and preventive frameworks must adapt to better address the intersection of substance use and interpersonal safety. Specifically, the authors recommend that mental health services routinely incorporate questions regarding cannabis use when conducting comprehensive evaluations of a person’s risk profile for violence. They contend that proactive screening could help clinicians identify vulnerable individuals earlier and provide more targeted interventions.
Additionally, the researchers advocate for a modernization of public health messaging surrounding cannabis. They argue that informational campaigns should explicitly include the potential connection between cannabis consumption and violence—both in terms of perpetration and victimization—so that consumers can make fully informed choices regarding their health and safety.
At the same time, the study’s authors emphasize a crucial scientific caveat: the review identifies a strong statistical association rather than proving direct causality. Cannabis use frequently co-occurs with a multitude of other complex socio-environmental and behavioral factors that are independently known to elevate the risk of violent behavior or victimization. These confounding variables include alcohol consumption, the use of other illicit or recreational drugs, and difficult social or economic circumstances, all of which must be carefully considered when interpreting the data.
Important Limitations of the Research
While the review represents one of the most comprehensive syntheses of cannabis-related behavioral data to date, the authors are transparent about several limitations inherent in the underlying literature. Most notably, only a small fraction of the studies included in the review measured quantitative metrics regarding how much cannabis people consumed or the precise frequency of their use. Consequently, the research could not conclusively determine whether casual, occasional use carries the same degree of risk as heavy, chronic consumption.
Furthermore, the findings involving criminal convictions were based upon a relatively limited number of studies, meaning that judicial outcomes should be interpreted with appropriate caution. Another critical consideration involves the temporal nature of the source data: the vast majority of the research evaluated was conducted prior to the widespread commercial availability of high-potency cannabis products. The researchers suggest that the daily use of today’s significantly more potent formulations could potentially be associated with even stronger effects, highlighting an urgent need for contemporary, forward-looking research as global drug markets continue to evolve.
The study received essential financial support from the National Institute for Health and Care Research (NIHR) Biomedical Research Centre based at Maudsley and the Medical Research Council under grant reference MR/T007818/1. The authors noted that the views, interpretations, and conclusions expressed within the study and its associated communications are strictly those of the researchers themselves and do not necessarily reflect the official positions of the NIHR or the Department of Health and Social Care.