The goal of the current study was to use a developmental framework to investigate the relationship between polygenic influences, close friend substance use, and their interaction on heavy episodic drinking patterns during the period from adolescence to young adulthood, while simultaneously controlling for other social processes (i.e., parental knowledge, broader peer group substance use) that may confound close peer effects. Generalized linear mixed models were used to account for age-related variability in heavy episodic drinking patterns (Chassin et al., 2002), as well as to examine genetic and environmental influences on the initial status and subsequent trajectories. In line with previous GxE investigations on adolescent substance use (e.g., Harden et al., 2008; Mrug and Windle, 2014; Salvatore et al., 2014a), it is hypothesized that individuals with high PRS for alcohol dependence will have a more rapid escalation of heavy episodic drinking over time compared to individuals with low PRS, and that close friend substance use will moderate this association such that the increased prevalence of substance use among close friends will accelerate heavy episodic drinking trajectories among these individuals.
