Early initiation of substance use is associated with many negative outcomes, including increased risk for developing substance use disorders (1–6), lower educational attainment (7, 8), early sexual debut, and risky sexual behaviors (9–11). Age at onset of alcohol, cigarette, and cannabis use is influenced by genetic and familial environmental factors (12, 13), some of which are common across substances (3, 14). A recent twin study found that a common factor accounted for 15% – 43% of the genetic influences on age at initiation of alcohol, tobacco, and cannabis, and also contributed 18% to 77% of the shared environmental variance in initiation of each substance, suggesting that the family environment plays a significant role in age at initiation of multiple substances (14). Parental alcohol use disorders (AUDs) affect the family environment shared by offspring in multiple ways that increase the likelihood of early substance use. In households where one or both parents has an AUD, there is a greater incidence of parental separation (15, 16), childhood trauma (15, 17), and decreased parental monitoring of child behavior (18, 19), factors which have
