We recorded clear and consistent associations and dose-response relations between the frequency of adolescent cannabis use and all adverse young adult outcomes. After covariate adjustment, compared with individuals who had never used cannabis, those who were daily users before age 17 years had clear reductions in the odds of high-school completion (adjusted odds ratio 0·37, 95% CI 0·20–0·66) and degree attainment (0·38, 0·22–0·66), and substantially increased odds of later cannabis dependence (17·95, 9·44–34·12), use of other illicit drugs (7·80, 4·46–13·63), and suicide attempt (6·83, 2·04–22·90).
Unadjusted odds ratios (log scale) between maximum frequency of cannabis use before age 17 years and young adult outcomes in combined data, compared with individuals who have never used cannabis
Adjusted odds ratios (log scale) between maximum frequency of cannabis use before age 17 years and young adult outcomes in combined data, compared with individuals who have never used cannabis
Data are n/N (%). ATP=Australian Temperament Project. CHDS=Christchurch Health and Development Study. VAHCS=Victorian Adolescent Health Cohort Study.
*p value of the association between adolescent cannabis use and each outcome in each study, and in combined data adjusted for study-specific effects.
†The ATP did not assess suicidal behaviour.
‡Assessed at age 28–30 years.