In a population of nearly 10 million Ontarians, ER visits for substance-induced psychosis were linked to a 163-fold increased risk of developing schizophrenia, with cannabis carrying the highest transition risk of any substance.
Mental health professionals, cannabis users concerned about psychosis risk, policymakers, parents of young cannabis users.
Cannabis-induced psychosis: 241-fold increased risk of schizophrenia transition
What the researchers found
Among 9.8 million people without prior psychosis, those with ER visits for substance-induced psychosis had a 163-fold increased risk of transitioning to schizophrenia (3-year risk: 18.5% vs 0.1%). Cannabis-induced psychosis had the highest transition risk (aHR 241.6). Even substance use ER visits without psychosis carried a 9.8-fold risk, and because they were far more common, they accounted for 3 times more total transitions than psychosis visits.
Why it matters
This is one of the largest studies to quantify the pathway from substance-related ER visits to schizophrenia. The finding that cannabis carried the highest transition risk among all substances, and that even non-psychotic substance use visits predicted elevated risk, has major implications for early intervention.
The numbers in context
9.8 million people studied. 407,737 ER visits for substance use. 13,784 (3.4%) involved psychosis. Substance-induced psychosis: 163-fold risk, 18.5% three-year transition rate. Cannabis psychosis: aHR 241.6. Non-psychotic substance use: 9.8-fold risk, 1.4% three-year rate, but 3x more total transitions (9,969 vs 3,029).
How the study worked
Population-based retrospective cohort study of 9.8 million individuals aged 14-65 in Ontario, Canada (January 2008 to March 2022), with no prior psychotic disorder. Used cause-specific hazard models to estimate transition risk to schizophrenia spectrum disorder.
What this study cannot tell us
Observational design cannot prove causation. Relies on ER diagnostic coding which may miss or misclassify cases. Ontario has universal healthcare which may limit generalizability to other systems. Cannot account for frequency or potency of substance use.
How to read the evidence
Population-based study of nearly 10 million people with 14 years of follow-up in a universal healthcare system, providing strong statistical power.
When this study was published
Published 2023, using 2008-2022 data from Ontario, Canada.
The bigger picture
The study highlights a critical but often overlooked finding: while substance-induced psychosis gets the most attention, the sheer volume of non-psychotic substance use ER visits means they produce far more schizophrenia cases overall. This suggests screening and follow-up for all substance-related ER visits, not just psychosis episodes.
Questions still open
- What specific interventions after substance-related ER visits could reduce schizophrenia transition rates?
- Does cannabis potency influence the transition risk from psychosis to schizophrenia?
Common questions
How much does cannabis-induced psychosis increase schizophrenia risk?
Can substance use without psychosis still lead to schizophrenia?
Read the original research
Transition to Schizophrenia Spectrum Disorder Following Emergency Department Visits Due to Substance Use With and Without Psychosis.
JAMA psychiatry, 80(11), 1169-1174
Citation
Myran, Daniel T; Harrison, Lyndsay D; Pugliese, Michael; Solmi, Marco; Anderson, Kelly K; Fiedorowicz, Jess G; Perlman, Christopher M; Webber, Colleen; Finkelstein, Yaron; Tanuseputro, Peter. (2023). Transition to Schizophrenia Spectrum Disorder Following Emergency Department Visits Due to Substance Use With and Without Psychosis.. JAMA psychiatry, 80(11), 1169-1174. https://doi.org/10.1001/jamapsychiatry.2023.3582
Explore the wider topic
- How THC Affects Your Amygdala: The Brain's Threat Detector and Cannabis
- The Anandamide Connection: Your Body's Natural Bliss Molecule
- How Long for Cannabinoid Receptors to Return to Normal
- Cannabis and the Developing Brain: What Every Teenager (and Parent) Should Know
- Why Can't I Enjoy Anything Without Weed? The Science Behind It
- Dopamine Recovery After Quitting Weed: What the Science Says
- The Endocannabinoid System Explained Simply: What It Does and Why It Matters
- Your Endocannabinoid System Explained: Why Withdrawal Happens
- Your Nervous System After Quitting Weed: Fight or Flight
- Using Weed Under 18: What It Does to Your Developing Brain
- What THC Does to Your Brain: Why Withdrawal Happens
- THC and Your Prefrontal Cortex: What Cannabis Does to Your Decision-Making Brain
- Weed, Cortisol, and Stress: What Cannabis Does to Your Stress Hormones
- Weed and Memory: What the Science Says About THC and Your Hippocampus
- Weed and Motivation: Is Amotivational Syndrome Real?
- Weed and Your Nervous System: What THC Actually Does to Your Brain and Body
- How Weed Rewires Your Reward System (And How to Reset It)