Rates of Cannabis Use Disorder Associated With Schizophrenia and Psychosis Increased With Cannabis Legalization in Canada

Cannabis use is associated with the development of psychosis and schizophrenia; frequent use of a high-potency product may elevate this risk. This study investigated the population-attributable fraction (PARF) for cannabis use disorder (CUD) associated with schizophrenia and psychosis not otherwise specified (NOS) in the province of Ontario, Canada across three cannabis policy periods.* Researchers leveraged retrospective population-based data of Ontario residents (ages 18–64), 2006–2022.

• PARF for CUD associated with schizophrenia significantly increased from 4 percent (pre-legalization) to 10 percent (post-legalization). The highest PARF was seen in men 19–24 years of age, post-legalization.
• PARF for CUD associated with psychosis NOS significantly increased from 5 percent (pre-legalization) to 12 percent (post-legalization).
• Gradual increases in PARF for CUD associated with schizophrenia occurred across all policy periods, while an acceleration in PARF for CUD associated with psychosis NOS after medical cannabis liberalization was noted.

* Canadian policy reform encompassed three distinct periods: pre-legalization (2006–2015), liberalization of medical cannabis and non-medical cannabis (2015–2018), and legalization of non-medical cannabis (2018–2022).

Comments: While CUD associated with psychosis NOS accelerated with liberalization of cannabis in this population, the steady increase of CUD associated with schizophrenia across policy reform periods suggests that other factors could be at play (i.e., drop in perceived risk, increased potency, and accessibility of products on the market). Rates of new CUD diagnoses associated with shifts in cannabis policy could be the subject of future studies to inform policymakers as they weigh decisions related to cannabis reform.

Emily Nields, DO

Reference: Myran DT, Pugliese M, Harrison LD, et al. Changes in incident schizophrenia diagnoses associated with cannabis use disorder after cannabis legalization. JAMA Netw Open. 2025;8(2):e2457868.