Age-dependent association of cannabis use with risk of psychotic disorder.

Abstract

Background: Epidemiologic research suggests that youth cannabis use is associated with psychotic disorders. However, current evidence is based heavily on 20th-century data when cannabis was substantially less potent than today.

Methods: We linked population-based survey data from 2009 to 2012 with records of health services covered under universal healthcare in Ontario, Canada, up to 2018. The cohort included respondents aged 12-24 years at baseline with no prior psychotic disorder (N = 11 363). The primary outcome was days to first hospitalization, ED visit, or outpatient visit related to a psychotic disorder according to validated diagnostic codes. Due to non-proportional hazards, we estimated age-specific hazard ratios during adolescence (12-19 years) and young adulthood (20-33 years). Sensitivity analyses explored alternative model conditions including restricting the outcome to hospitalizations and ED visits to increase specificity.

Results: Compared to no cannabis use, 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). When we restricted the outcome to hospitalizations and ED visits only, the strength of association increased markedly during adolescence (aHR = 26.7; 95% CI 7.7-92.8) but did not change meaningfully during young adulthood (aHR = 1.8; 95% CI 0.6-5.4).

Conclusions: This study provides new evidence of a strong but age-dependent association between cannabis use and risk of psychotic disorder, consistent with the neurodevelopmental theory that adolescence is a vulnerable time to use cannabis. The strength of association during adolescence was notably greater than in previous studies, possibly reflecting the recent rise in cannabis potency.