Sources of exposure to smoking and drinking friends among adolescents: a behavioral-genetic evaluation.

Substance-using friends expose adolescents to models of, and opportunities for, substance use that may lead to its initiation or reinforce existing use. Using genetically informative data from the National Longitudinal Study of Adolescent Health (P. S. Bearman, J. Jones, & J. R. Udry, 1998), the authors examined whether adolescents' exposure to friends' tobacco smoking and alcohol drinking was better explained by family-social or genetic influences. To conduct analyses, the authors constructed substance use exposure scores for adolescent siblings from the responses of siblings' nominated friends to self-reported smoking and drinking items. Using behavioral-genetic analyses of these substance use exposure scores, the authors estimated that 64% of the variance in adolescents' exposure to friends who smoke and drink could be explained by genetic influences, whereas shared environmental influences were zero. These results provide evidence of active, evocative, or both types of gene-environment correlations. Genetic factors can influence the formation of friendships with substance-using peers, thereby contributing to adolescents' exposure to substance use behaviors.