A study published on June 17 in The Lancet Psychiatry reports that the commercial sale of cannabis is associated with increased health risks, including higher rates of addiction. The research, led by experts at the University of Bath in the UK and an international team, found that removing criminal penalties for personal possession or introducing tightly controlled legalization does not appear to increase overall levels of cannabis use.
The study examined global changes in cannabis policy between 2000 and 2025 and analyzed their impact on cannabis use, addiction, and psychiatric disorders. Co-authors Professor Tom Freeman and Dr. Rachel Lees Thorne from the Department of Psychology at Bath said their findings highlight distinct effects from different policy approaches worldwide.
According to the researchers, countries such as Uruguay have adopted tightly controlled legal frameworks for adult access to a restricted range of products. In these contexts, there was little evidence for changes in overall cannabis use following legalization. By contrast, many US states and Canada have implemented commercialized legal markets where for-profit sales make potent products widely available. In these environments, both usage rates and cases of addiction among adults have risen.
Professor Freeman said: "We found little evidence for changes in use after decriminalisation or tightly controlled legalisation. By contrast, in Canada and the US, policy changes have been more substantial through commercialised legalisation, which have increased sales and consumption." He added, "There are now more daily consumers of cannabis than daily consumers of alcohol in the US. What followed commercialised legalisation was a rise in cannabis addiction as well as increases in hospital admissions for psychosis..."
The study also reviewed medical cannabinoids' effectiveness based on clinical trials. Across 54 trials, cannabinoids showed limited benefits—modestly reducing withdrawal symptoms or improving sleep—but did not show meaningful effects on anxiety disorders or opioid dependence.
Freeman concluded: "As global cannabis policies continue to evolve, we need to do more to track their impact – particularly in countries outside of the US and Canada..." The new review is part of a collection published by The Lancet Psychiatry with contributions from international partners.
