Commercial Cannabis Markets Linked to Higher Use, Addiction, and Psychosis: Global Study Findings

The Lancet Psychiatry study, published 17 June 2024 and led by Professor Tom Freeman and Dr Rachel Lees Thorne of the University of Bath, analysed cannabis-policy shifts in 30 jurisdictions from 2000 to 2025. De-criminalisation or tightly regulated legalisation—exemplified by Uruguay’s pharmacy-based system—showed little change in consumption. By contrast, commercial for-profit markets in the United States and Canada were linked to higher THC potency, increased daily use, and greater addiction rates.

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In the United States, daily cannabis users now outnumber alcohol users. Commercial markets have raised THC concentrations and spurred a surge in psychosis admissions, often co-occurring with cannabis-use disorder. While psychosis incidence does not consistently rise, the admission increase signals heightened risk from high-potency products.

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A review of 54 trials from institutions including the University of Queensland, NYU Grossman School of Medicine and the University of Toronto found modest benefits of cannabinoids for cannabis-withdrawal relief, insomnia and autism-related traits. No meaningful improvement was found for anxiety, PTSD, psychosis, opioid dependence or depression; one trial noted increased cocaine craving. No trials examined depression outcomes.

Legalising cannabis increases use and addiction – unless it's tightly controlledNeuroscience News

Professor Freeman stressed that “the type of policy change is critical” and called for monitoring. Dr Lees Thorne highlighted separating criminal-justice harms from health risks. The London Drugs Commission’s 2025 report, commissioned by Mayor Sadiq Khan, recommends de-criminalising possession to shift enforcement toward healthcare and reduce policing of Black communities. UK Advisory Council on the Misuse of Drugs is reviewing the 2018 medical-cannabis regime. Funding came from UK Research and Innovation.

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The authors criticize for-profit cannabis markets for prioritising profit over health, likening them to the alcohol and tobacco industries. While the review found no consistent link between policy shifts and psychosis prevalence, commercial markets were associated with increased psychosis-related admissions. Evidence from Europe, Africa, Oceania and Asia remains limited, restricting assessment of de-criminalisation effects outside North America. Long-term outcomes of tightly regulated models like Uruguay’s require further study.

Legalising cannabis increases use and addiction – unless it's tightly controlled

• “We found little evidence for changes in use after decriminalisation or tightly controlled legalisation.” — Prof Tom Freeman, University of Bath

Legalising cannabis increases use and addiction – unless it's tightly controlled

• “There are now more daily consumers of cannabis than daily consumers of alcohol in the US.” — Prof Tom Freeman

Legalising cannabis increases use and addiction – unless it's tightly controlled

• “The emergence of a for-profit cannabis industry can result in commercial interests being prioritised over public health – just as we have seen with the alcohol and tobacco industries.” — Prof Tom Freeman

Legalising cannabis increases use and addiction – unless it's tightly controlled

• “Alternative policies – such as decriminalisation or strictly regulated legalisation – can remove the harms of criminalising people who use cannabis, while limiting changes in use.” — Prof Tom Freeman

Legalising cannabis increases use and addiction – unless it's tightly controlled