Childhood cigarette and alcohol use were the strongest predictors of early cannabis use, with family factors also contributing

Among 852 adolescents, 10.7% showed early-onset cannabis use (before age 15). The strongest predictors were childhood cigarette use and drinking until drunk. Family factors (poor management, antisocial family history, parent attachment) predicted early onset specifically. Cumulative risk from early substance use was the strongest independent predictor of both early-onset cannabis use (RRR 2.64, CI 1.40-4.97) and late-onset occasional use (27%). Family-related cumulative risk also predicted late-onset use.

Prospective longitudinal study of 852 adolescents (53% female) from the Australian International Youth Development Study, with risk/protective factors measured in fifth grade (mean age 10.9) and cannabis use measured at 6 time points from ages 12-19.

Prevention is most effective when targeted at the right age. This study identifies fifth-grade risk factors that predict cannabis trajectories years later, offering a specific prevention window and specific targets (early substance use, family environment).

The finding that early alcohol and cigarette use outpredict family and peer factors for cannabis onset reinforces the gateway sequence: legal substance use in childhood is the strongest entry point. Delaying first alcohol and cigarette use may be the most effective cannabis prevention strategy.

Australian sample (may not generalize to other contexts); self-report at all time points; 53% female (slightly unbalanced); risk factors measured at single time point in fifth grade; does not assess cannabis potency or type.