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Age-Dependent Association Found Between Cannabis Use and Psychosis
Cannabis use was significantly associated with psychotic disorders during adolescence, but not during young adulthood, according to results from an observational study published in Psychological Medicine.
“This study found a strong but age-dependent association between cannabis use and psychotic disorders, consistent with the theory that adolescence is a particularly vulnerable time to use cannabis as the brain is still developing,” noted lead author André J. McDonald, Epidemiology Division, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada, and co-authors. “Based on the precautionary principle, as more jurisdictions move to liberalize cannabis use and perception of harm declines among youth, this study suggests that evidence-based cannabis prevention strategies for adolescents are warranted.”
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Researchers linked 2009-2012 population-based survey data with Ontario's universal health care records up to 2018, focusing on respondents aged 12-24 years with no prior psychotic disorder (N = 11,363). The primary outcome was the time to the first hospitalization, ED visit, or outpatient visit for a psychotic disorder. Researchers analyzed using age-specific hazard ratios for adolescence (12-19 years) and young adulthood (20-33 years).
Cannabis use was significantly associated with psychotic disorders during adolescence (aHR = 11.2; 95% CI 4.6–27.3) but not during young adulthood (aHR = 1.3; 95% CI 0.6–2.6), compared with no cannabis use. Restricting the outcome to hospitalizations and ED visits increased the association's strength during adolescence (aHR = 26.7; 95% CI 7.7–92.8) but did not significantly change it during young adulthood (aHR = 1.8; 95% CI 0.6–5.4), researchers noted.
Researchers noted some study limitations, including the inability to control for unmeasured confounders and the inability to establish temporality between exposure and outcome. The study had only a single baseline measurement of substance use, contributing to potential exposure misclassification and time-varying confounding bias. Reliance on self-reported cannabis use, collected when recreational use was illegal, likely led to underreporting, and the dataset lacked details on THC potency, mode of use, product type, or cannabis dependence. Additionally, the sample excluded institutionalized and homeless youth, groups at high risk for both cannabis use and psychotic disorders.
“Further longitudinal studies using contemporary data with more sophisticated cannabis measurement and a more comprehensive set of baseline and time-varying confounders are needed to strengthen causal inference,” authors concluded.
