A new study published in JAMA Network Open has revealed a nearly threefold increase in schizophrenia cases linked to cannabis use disorder (CUD) following the legalization of nonmedical cannabis. The research highlights concerns over the potential mental health impact of widespread cannabis use and the need for ongoing monitoring of policy changes.

Study Details and Key Findings

Conducted by Dr. Daniel T. Myran and colleagues at the Ottawa Hospital Research Institute in Canada, the population-based cohort study examined data from 13.5 million individuals aged 14 to 65 who had no prior history of schizophrenia. The researchers aimed to determine how the proportion of schizophrenia cases linked to CUD changed before and after cannabis policy reforms in Canada.

According to the findings, 0.9% of participants had CUD, and 0.7% developed schizophrenia. Among individuals with CUD, the schizophrenia rate was significantly higher at 8.9%. The population-attributable risk fraction (PARF) for CUD-associated schizophrenia nearly tripled from 3.7% in the prelegalization period to 10.3% after nonmedical cannabis was legalized.

The impact varied across demographics, with men aged 19 to 24 experiencing the highest postlegalization PARF at 18.9%, while women aged 45 to 65 had the lowest at 1.8%. Although the overall incidence of schizophrenia remained stable, cases of psychosis not otherwise specified (NOS) increased significantly, from 30.0 to 55.1 per 100,000 individuals.

Concerns Over Cannabis Policy and Mental Health

The study also observed a steady rise in schizophrenia cases linked to CUD over time, with no sudden accelerations following policy changes. However, after medical cannabis liberalization, CUD-related psychosis NOS cases surged, raising concerns about the potential risks associated with increased cannabis accessibility.

The findings underscore the need for continued research into the long-term effects of cannabis policy changes on public mental health. "Ongoing research is needed on long-term trends in the incidence of psychotic disorders associated with changes in cannabis policy," the study authors emphasized.

As cannabis use becomes more widespread, health experts urge policymakers to consider stronger public health strategies, including awareness campaigns and mental health screenings, to mitigate potential risks associated with cannabis use disorder.