Jodi Gilman from Massachusetts General Hospital emphasizes the necessity for comprehensive epidemiological studies to evaluate the long-term mental health impacts of cannabis legalization, particularly on vulnerable groups.

The research highlights a significant public health challenge posed by the increased potency and frequency of cannabis use, especially among youth.

These findings underscore the urgent need for ongoing research into the long-term consequences of cannabis policy on the prevalence of psychotic disorders.

A recent study has established a concerning link between Canada's cannabis legalization and a notable rise in schizophrenia cases associated with cannabis use disorder (CUD) in Ontario.

The population-attributable risk fraction (PARF) for CUD related to schizophrenia surged from 3.7% before legalization to 10.3% during the legalization period.

Following the legalization of non-medical cannabis in 2018, emergency department visits and hospitalizations for CUD skyrocketed by 270%, highlighting the growing public health concern.

It is estimated that approximately 10% of new schizophrenia cases during the legalization phase could have been avoided if individuals with severe CUD had stopped using cannabis, with this figure increasing to 18% for young men aged 14 to 24.

Published online on February 4, 2025, in JAMA Network Open, the study received support from the Canadian Institutes of Health Research and ICES.

Study investigator Daniel Myran cautions that legalization does not eliminate the risks associated with cannabis use, similar to the dangers posed by legal substances like alcohol and tobacco.

The significant increase in schizophrenia cases linked to CUD indicates an urgent need for targeted prevention strategies, particularly aimed at younger populations.

Utilizing robust health administrative data, the study assessed the effects of cannabis policy changes on mental health outcomes over time.

While the study does not definitively establish that heavy cannabis use causes schizophrenia, it suggests that regular users may experience earlier onset and more severe symptoms.