Since substance use does not emerge developmentally before adolescence, the role of DRD4 in substance use and addiction can be studied only in adolescents and adults. In studies examining alcohol use, peer influences on heavy drinking were stronger among young adults (age 18-28) with the long DRD4 allele (Larsen et al., 2010). Similarly, emerging adults involved in college or Greek organizations who had the long DRD4 allele reported more alcohol dependence symptoms (Park et al., 2011). However, another study with adolescents (ages 13-18) failed to find increased susceptibility to peer influences on alcohol use among those with high risk DRD4 polymorphism (van der Zwaluw et al., 2012), and parenting influences on regular alcohol (or cannabis) use did not vary across DRD4 genotypes in another adolescent study (Creemers et al., 2011). Similarly conflicting results have been reported for smoking outcomes. For instance, adults with the long DRD4 allele smoked more in response to smoking cues and negative affect induction (Hutchison et al., 2002; Perkins et al., 2008), but the effects of smoking-related parenting behaviors on adolescent smoking outcomes did not vary across DRD4 genotypes (Hiemstra et al., 2013).
