A new review has found that decriminalizing cannabis possession or strictly regulating access does not appear to increase usage, but commercial sales lead to more users and higher rates of psychosis. The study, published in Lancet Psychiatry, analyzed global policy shifts from 2000 to 2025.
Commercial Markets Drive Increases
In regions like the US and Canada, where commercial cannabis markets opened, researchers observed more users, higher drug potency, and increased hospital visits for psychosis. In contrast, decriminalization in Europe, Africa, Oceania, and Asia showed little change in usage or psychiatric illness. Uruguay, which legalized cannabis but tightly controls it, saw similar results to decriminalization.
Tom Freeman, professor of psychology at the University of Bath and lead author, said: “When we look globally, there’s been a rapid shift towards more liberal cannabis policies. That gives us a chance to evaluate what happened from before to after.”
Policy Implications
Freeman noted the findings are “encouraging” for policymakers considering decriminalization or strict regulation. However, open markets resemble alcohol and tobacco sales, where profit motives lead to cheaper, higher-potency products. “When there’s a for-profit industry, particularly for an addictive product, there’s an incentive to sell cheaper products, and high-potency products,” he added.
In the UK, cannabis remains a class B drug with penalties of up to five years in prison. A 2023 report by the London Drugs Commission, commissioned by Mayor Sadiq Khan, proposed decriminalizing recreational use, citing racial disparities in enforcement.
Expert Consensus
Sir Robin Murray, professor at King’s College London, said: “Commercialisation of supply rather than simple legislation for recreational use is the critical factor.” He warned that in North America, legalization led to “rampant commercialisation” driven by advertising. Alex Stevens, professor at the University of Sheffield, called the review “absolutely essential” for policymakers, noting that restricted regulation and decriminalization do not necessarily increase use.
