Previous research finds drug-using peers and religiosity to be key predictors of drug use among youth, but the effects of childhood exposure to drug users and religion on later drug use have been understudied. The authors hypothesize a child's exposure to parental drug use and religious upbringing have a causal influence on drug use in youth primarily through drug-using peer association and religiosity during adolescence and young adulthood. To test this hypothesis, the authors analyze nationally representative three-wave panel data spanning ages 6 to 22. Results from estimating a structural equation model provide empirical support for the hypothesis, as the causal influence was found to be indirect via the proximate predictors of drug use among youths; that is, childhood risk and protective factors were positively associated with their adolescent and young adulthood counterparts, which in turn had a causal effect on drug use by youth. (Contains 2 figures, 2 tables, and 6 notes.)