To examine Hypothesis 1 analyses were conducted to determine the moderating role of OXTR risk on the relationship between Intervention Status and substance-using peer affiliations. The first model, a regression model, included main effects for Intervention Status and OXTR risk. Both intervention status (b = −0.07, p < .01) and OXTR (b = 0.03, p < .01) predicted affiliation with substance-using friends such that adolescents in the intervention had fewer substance-using friends and higher OXTR risk was related to having more substance-using friends. In the second model, a two-way interaction between Intervention Status and OXTR risk was added to the first, which was significant (b = 0.06, p < .01). The interaction remained significant after controlling for PC1. Figure 2 illustrates that OXTR variability was not associated with 9th-grade peer substance use within the control group, but had substantial effect in the intervention condition. Figure 2 shows that affiliations with substance-using friends were never higher in the intervention condition than in the control condition. In fact, the intervention appeared to provide a protective effect among low OXTR risk youth in
