A longitudinal analysis of friendships and substance use: bidirectional influence from adolescence to adulthood.

The reciprocal relation between deviant friendships and substance use was examined from early adolescence (age 13-14) to young adulthood (age 22-23). Deviance within friendships was studied using direct observations of videotaped friendship interaction and global reports of deviant interactions with friends as well as time spent with friends. Substance use was assessed through youth self-report at all time points. Multivariate modeling revealed that substance use in young adulthood is a joint outcome of friendship influence and selection processes. In addition, substance use appears to influence the selection of friends in late adolescence. Findings suggest that effective preventions should target peer ecologies conducive to substance use and that treatment should address both the interpersonal underpinnings and addiction processes intrinsic to chronic use, dependence, and abuse.