level of genetic contribution to alcohol use (Guo et al., 2009). Similar findings have been reported by Dick and colleagues (2007) who reported that as peer alcohol use increases, heritable factors associated with an adolescent’s own alcohol involvement also increase. In addition to a gene by environment interaction, evidence for gene by environment correlation in which individuals with increased genetic liability for substance use are more likely to affiliate with substance-using peers has also been provided (Agrawal et al., 2010; Harden et al., 2008). Considering that the extent to which an individual affiliates with substance-using or delinquent peers has emerged as one of the strongest correlates of adolescent onset substance use and substance use problems, it is critical to consider this variable in a model of predictors of alcohol-related problems among adolescents.
