Summary of peer-reviewed studies and authoritative reports

Key Takeaways for Legislators

  1. Cannabis–absent a pre-existing condition–does not cause psychosis or schizophrenia.
  2. Risk is confined to individuals with predisposing genetic or environmental factors.
  3. Scientific consensus: schizophrenia is primarily a neurodevelopmental disorder, not a drug-induced one.
  4. Policy implications: Blanket bans on cannabis “based on psychosis concerns”, are not supported by evidence.

 

Study / Link Scope / Findings Key Conclusion
The Lancet: High-potency cannabis and psychosis risk Review of cannabis and psychosis studies; evaluated genetic/environmental confounders Most studies cannot fully adjust for genetic/environmental differences. Claims that high-potency cannabis causes psychosis are likely overestimated.
PsychCentral: Harvard study – Cannabis does not cause schizophrenia Familial risk study Increased risk of schizophrenia in cannabis users is likely due to family history, not cannabis itself.
NIH: Substance-Induced Psychotic Disorder Study Individuals with high familial risk of substance abuse or psychosis Psychosis occurs in vulnerable individuals after substantial drug exposure. Cannabis is a trigger, not a cause, in predisposed individuals.
Psychology Today: Can marijuana cause psychosis? Review of cannabis and psychosis No definitive evidence that cannabis alone induces psychosis. Risk is elevated only in young daily users with genetic predisposition.
Very Well Mind: Does marijuana cause psychosis? Review of co-occurring mental health and substance use disorders Cannabis may trigger psychotic episodes only in individuals already predisposed.
UK Advisory Council on the Misuse of Drugs: Cannabis Report (2008) Policy review Most young cannabis users do not develop psychosis. Those who do have predisposing factors (genetic/environmental). No causal link found with affective disorders.
SAGE Journals: Cannabis use and risk review Comparison of cannabis, tobacco, alcohol risks Association between moderate cannabis use and psychosis is weaker than for tobacco, and alcohol poses far greater risk for accidents.
NIH: Predictors of cannabis-related mental disorders Large cohort study Risk factors for cannabis-related mental disorders include prior substance use, other mental disorders, age, not cannabis use alone.
JAMA Network: State Cannabis Legalization and Psychosis-Related Health Care Utilization 63+ million insurance claims, 2003–2017 No significant differences in psychosis-related diagnoses or antipsychotic prescriptions in states with cannabis policies vs. states without.
PubMed: Cannabis use and psychosis transition study Longitudinal cohort No significant association between cannabis use and transition to psychosis, symptom persistence, or functional outcome.
University of Alberta: Commentary on cannabis and schizophrenia Neuroscience perspective Schizophrenia origins are neurodevelopmental, beginning during gestation. Cannabis does not cause schizophrenia.