A prospective study of the effects of age of initiation of alcohol and drug use on young adult substance dependence

Objective: Previous cross-sectional research has disagreed about whether an adolescent's age of onset of alcohol use is a unique predictor of later alcohol dependence or whether it is merely a correlate of those factors that produce alcohol dependence. The current study tests this question in a longitudinal sample, and extends the literature by testing whether age of onset of alcohol and drug use predicts alcohol and drug dependence. Method: Data from an ongoing study of children of alcoholics and matched controls (n = 395) were collected during three annual interviews during adolescence and two 5-year follow-ups in young adulthood. Results: Taking a first drink of alcohol at or before age 13 was unrelated to the odds of alcohol and drug dependence when the adolescent did not also participate in early drug use or when correlated risk factors were taken into account. On the other hand, early drug use elevated the odds of drug dependence by young adulthood, even while controlling for shared risk factors. Conclusions: The current study provides support for the notion that early-adolescent onset of alcohol use is a marker of risk for later dependence rather than a causal influence. Moreover, it provides evidence for the impact of early drug use on drug-substance dependence. Implications for theory and intervention are discussed.