That affiliation with substance-using friends is similarly linked to individual adolescents’ alcohol use across all combinations of intervention and OXTR risk is important. Findings suggest that the interactive effects of OXTR variation manifest more in terms of peer selection than peer influence. The shape of the OXTR by intervention interaction is important. First, rather than crossing over, the interaction took on a fan-shape, whereby the intervention appears to facilitate the ability of low OXTR risk adolescents to select peers engaging in very low levels of substance use. Perhaps such adolescents, without the intervention, would minimize or ignore their friends’ substance use out of loyalty or empathy. Given that across all combinations of OXTR risk and intervention vs. control conditions, affiliating with peers who use fewer substances appears to be better than affiliating with higher-use peers, the ability of the intervention to positively impact this peer context is important.
