Increase Seen in Cases of Schizophrenia Linked to Cannabis Use Disorder

Schizophrenia-associated increase seen from prelegalization to legalization of nonmedical cannabis periods

By Elana Gotkine HealthDay Reporter

FRIDAY, Feb. 7, 2025 (HealthDay News) — The proportion of incident cases of schizophrenia associated with cannabis use disorder (CUD) almost tripled from the prelegalization to legalization of nonmedical cannabis periods, according to a study published online Feb. 4 in JAMA Network Open.

Daniel T. Myran, M.D., M.P.H., from the Ottawa Hospital Research Institute in Ontario, Canada, and colleagues conducted a population-based cohort study among 13,588,681 people aged 14 to 65 years without a history of schizophrenia to examine changes in the population-attributable risk fraction (PARF) for CUD associated with schizophrenia after liberalization of medical cannabis and legalization of nonmedical cannabis in Canada.

Of the participants, 0.9 percent had CUD. The researchers found that 0.7 percent of individuals in the cohort developed schizophrenia (0.6 percent in the general population and 8.9 percent of those with CUD). From the prelegalization to legalization periods, there was an almost threefold increase in the PARF for CUD associated with schizophrenia from 3.7 to 10.3 percent. The PARF in the postlegalization period varied from 18.9 to 1.8 percent among men aged 19 to 24 years and women aged 45 to 65 years, respectively. Over time, the annual incidence of schizophrenia was stable, while the incidence of psychosis not otherwise specified (NOS) increased from 30.0 to 55.1 per 100,000 individuals in the postlegalization versus the prelegalization periods. During the study, there was a steady increase in the PARF for CUD associated with schizophrenia, with no accelerations observed after cannabis policy changes. After medical cannabis liberalization, increases in the PARF for CUD-associated psychosis NOS accelerated.

“Ongoing research is needed on long-term trends in the incidence of psychotic disorders associated with changes in cannabis policy,” the authors write.

One author disclosed ties to the pharmaceutical industry.