Risk for initiation of substance use as a function of age of onset of cigarette, alcohol and cannabis use: Findings in a Midwestern female twin cohort

Objective. We investigated whether use and early-onset use of cigarettes, alcohol and cannabis contributed an increase in risk for initiation of subsequent psychoactive substances in women (N = 3729, mean age = 21.7). Methods. Drugs were ordered in ascending order of initiation: cigarettes, alcohol, cannabis and other illicit drugs, with early-onset use of each drug used as a time-varving covariate to predict initiation of subsequent drugs. Interactions of use and early-onset use, with age of initiation of subsequent drugs, were evaluated using discrete-time Cox survival analyses. Results. The association between each substance and the early-onset of subsequent drug use was strong (ORs 1.54-19.9). Women who initiated cigarette, alcohol or cannabis use at an early age were at elevated risk for early experimentation with each subsequent drug class. Furthermore, early-onset of more than one substance contributed greater risk for initiation of subsequent drugs. Conclusion. Prevention efforts should target risk factors that contribute to early initiation of cigarette and alcohol use and may subsequently correlate with hard drug involvement. (c) 2006 Elsevier Inc. All rights reserved.