The current study uses a cGxE framework to examine the effect of the interactive relationship among OXTR status, affiliating with substance-using peers, and substance use interventions. This framework is uniquely suited to understanding for whom and why environments matter (Schlomer et al., 2015). Some critics of this method have indicated that single-gene approaches do not reflect how genetic variance impacts behaviors. This critique is true. However, the use of single genes, whether VNTRs, such as DRD4 or 5-HTTLPR, or via multiple SNPs, as we do here, comes with the advantage of understanding the role of specific genes on specific biological processes that in turn affect behaviors via neurocognitive processes and differences in individual characteristics. Although these pathways are not by any means fully understood, the use of genes with roles in these pathways provides the opportunity to gain greater insight into whom is being affected by interventions and why. Other approaches offer advantages as well. Although they are agnostic to the identity of specific genes, twin studies provide the basis for determining the existence and extent of genetic influences on
