Peer Alcohol Use Differentially Amplifies Genetic and Environmental Effects on Different Developmental Trajectories of Adolescent Alcohol Use

Purpose: The purpose of the study was to investigate how peer alcohol use moderates genetic and environmental influences on three different developmental trajectories of alcohol use during adolescence: low (continuously low levels of use), early-onset fast-escalating (initiated use early, the level of use increased quickly), and normative increasing (started at a low level and increased steadily) using biometric modeling. Methods: Data were from a longitudinal study on a sample of population-based adolescent twins (N = 842, 52.7% female, 84% European Caucasian). Adolescents self-reported past-year alcohol use at age 13, 14, 15, and 17 years. Adolescents' nominated friends reported their own past-year alcohol use at age 13, 15, and 17 years. Results: Genetic and environmental influences on adolescents' alcohol use trajectories were differentially moderated by friends' alcohol use in different trajectories. Gene-environment interaction was implicated in the low and early-onset trajectories, such that genetic contributions were amplified when friends used more alcohol. Environment-environment interaction was involved in the normative increasing and early-onset trajectories, such that person-specific environmental contributions were amplified when friends' alcohol use increased. Conclusions: Adolescent alcohol use remains a major public health issue, with peer alcohol use being a major risk factor. These findings suggest that close supervision to reduce deviant peer affiliation as well as preventions targeting peer group norms of alcohol use might be especially beneficial for adolescents following the normative increasing and early-onset trajectories. (C) 2019 Society for Adolescent Health and Medicine. All rights reserved.