Studies of alcohol, nicotine and illicit drug use disorders during adolescence are relatively uncommon as a majority of at-risk individuals meet criteria for abuse/dependence during early adulthood. Nonetheless, studies of one or more abuse/dependence symptoms during adolescence find strong evidence for the role of heritable influences (50% and greater).36,37 While the role of shared environment appears to be non-significant in adult studies of substance use disorders, it remains an important contributor to variation in adolescent substance use problems.38
