The Share of Schizophrenia Cases Linked to Cannabis Use Disorder Nearly Tripled After Legalization
In Ontario, the proportion of new schizophrenia cases attributable to cannabis use disorder rose from 3.7% before legalization to 10.3% after, reaching 18.9% among young men aged 19-24.
Quick Facts
What This Study Found
The population-attributable risk fraction (PARF) for CUD associated with schizophrenia nearly tripled from 3.7% pre-legalization to 10.3% post-legalization. Among males aged 19-24, the PARF reached 18.9%. The overall incidence of schizophrenia remained stable, but psychosis NOS increased 83.7% post-legalization. The PARF increase was steady over time without acceleration after specific policy changes.
Key Numbers
13,588,681 individuals; 118,650 (0.9%) had CUD; 91,106 (0.7%) developed schizophrenia; PARF rose from 3.7% to 10.3%; PARF for males 19-24 reached 18.9%; PARF for females 45-65 was 1.8%; psychosis NOS incidence rose from 30.0 to 55.1 per 100,000 (83.7% increase).
How They Did This
Population-based cohort study of 13.6 million Ontario residents aged 14-65 without prior schizophrenia history, from 2006-2022, using segmented linear regression to examine changes across three policy periods: pre-legalization, medical liberalization, and non-medical legalization.
Why This Research Matters
This is among the most comprehensive population-level studies linking cannabis policy changes to psychotic disorder burden. The finding that nearly 1 in 5 schizophrenia cases in young men may be attributable to CUD post-legalization carries significant public health implications.
The Bigger Picture
This study adds to a growing body of evidence connecting cannabis legalization, rising CUD rates, and psychotic disorder burden. The stable overall schizophrenia incidence alongside rising psychosis NOS suggests the diagnostic landscape may be shifting as cannabis-related presentations increase.
What This Study Doesn't Tell Us
Observational design cannot prove that CUD causes schizophrenia. The PARF increase was gradual and did not accelerate after specific policy changes, making it difficult to attribute directly to legalization versus other temporal trends. Reverse causation (psychosis prodrome leading to cannabis use) remains possible.
Questions This Raises
- ?Why did the PARF increase steadily rather than accelerating after legalization?
- ?Is the rising psychosis NOS incidence a precursor to future schizophrenia diagnoses?
- ?What specific components of cannabis policy (potency limits, advertising, access) could mitigate these trends?
Trust & Context
- Key Stat:
- 18.9% of new schizophrenia cases in young men (19-24) were associated with cannabis use disorder post-legalization
- Evidence Grade:
- Strong: Very large population-based cohort (13.6 million) published in JAMA Network Open with rigorous time-series analysis across three policy periods.
- Study Age:
- Published in 2025 with data from 2006-2022.
- Original Title:
- Changes in Incident Schizophrenia Diagnoses Associated With Cannabis Use Disorder After Cannabis Legalization.
- Published In:
- JAMA network open, 8(2), e2457868 (2025)
- Authors:
- Myran, Daniel T(16), Pugliese, Michael(13), Harrison, Lyndsay D(4), Solmi, Marco, Anderson, Kelly K, Fiedorowicz, Jess G, Finkelstein, Yaron, Manuel, Doug, Taljaard, Monica, Webber, Colleen, Tanuseputro, Peter
- Database ID:
- RTHC-07218
Evidence Hierarchy
Looks back at existing records to find patterns.
What do these levels mean? →Frequently Asked Questions
Does cannabis cause schizophrenia?
This study found a growing association between cannabis use disorder and schizophrenia diagnoses over time, but observational data cannot prove direct causation. Genetic vulnerability, other substance use, and reverse causation (early psychosis symptoms leading to cannabis use) are all possible factors.
Why did the trend not accelerate after legalization?
The PARF increased steadily from 2006 to 2022 without sharp jumps after policy changes. This suggests the relationship may reflect gradual increases in cannabis potency and CUD prevalence over time rather than an immediate effect of any single policy change.
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Cite This Study
https://rethinkthc.com/research/RTHC-07218APA
Myran, Daniel T; Pugliese, Michael; Harrison, Lyndsay D; Solmi, Marco; Anderson, Kelly K; Fiedorowicz, Jess G; Finkelstein, Yaron; Manuel, Doug; Taljaard, Monica; Webber, Colleen; Tanuseputro, Peter. (2025). Changes in Incident Schizophrenia Diagnoses Associated With Cannabis Use Disorder After Cannabis Legalization.. JAMA network open, 8(2), e2457868. https://doi.org/10.1001/jamanetworkopen.2024.57868
MLA
Myran, Daniel T, et al. "Changes in Incident Schizophrenia Diagnoses Associated With Cannabis Use Disorder After Cannabis Legalization.." JAMA network open, 2025. https://doi.org/10.1001/jamanetworkopen.2024.57868
RethinkTHC
RethinkTHC Research Database. "Changes in Incident Schizophrenia Diagnoses Associated With ..." RTHC-07218. Retrieved from https://rethinkthc.com/research/myran-2025-changes-in-incident-schizophrenia
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.