How cannabis policies shape use, disorder, and mental health outcomes

This comprehensive international review examined how different cannabis policy approaches affect usage rates, substance use disorders, and psychiatric health outcomes from 2000-2025. The research reveals a critical distinction between policy types: commercialised legal markets in Canada and the USA showed increased cannabis use, cannabis use disorder prevalence, and rising product potency among adults, while hospital admissions for psychosis and psychosis combined with cannabis use disorder also increased following legalisation. However, the relationship between policy and psychotic disorder prevalence remained inconsistent across studies, suggesting that simply legalising cannabis does not automatically cause population-wide increases in psychotic illness.

Importantly, the findings differentiate between commercial and non-commercial approaches to legalisation. Strictly regulated legalisation models—whether for medical or non-medical use—did not show strong associations with increased cannabis use or psychiatric harms, offering a potential middle ground between full prohibition and unrestricted markets. Meanwhile, poorly regulated medical cannabis access without rigorous efficacy and safety requirements emerged as a concern, while decriminalisation in Europe, Africa, Oceania, and Asia showed little evidence of increased cannabis use or psychiatric disorders, challenging assumptions that removing legal penalties automatically drives usage up.

These findings have significant implications for policymakers considering cannabis reform. The data suggests that how cannabis is legalised matters more than whether it is legalised—market commercialisation appears to be the key driver of increased use and related harms, not legalisation itself. The results support cautious, heavily regulated approaches to cannabis policy rather than either strict prohibition or open commercial markets, while highlighting the need for long-term monitoring of emerging policy models.