The purpose of this study was to investigate whether OXTR variation moderated intervention effects on both affiliations with substance-using peers and the impact of these affiliations on adolescents’ own alcohol use in the 9th grade. Analyses addressing affiliation revealed a two-way interaction with OXTR variation predicting peer substance use, whereby lower OXTR risk was linked to lower levels of peer substance use among intervention youth but not control youth. The interpretation of this interaction is straightforward: Within the intervention condition OXTR variation has a strong effect on the selection of substance-using friends, and no effect on the selection of those friends in the control condition.
