Trajectories of peer social influences as long-term predictors of drug use from early through late adolescence.

The present study analyzed the long-term effects of perceived friend use and perceived peer use on adolescents' own cigarette, alcohol and marijuana use as a series of parallel growth curves that were estimated in two developmental pieces, representing middle and high school (N = 1,040). Data were drawn from a large drug abuse prevention trial, the Midwestern Prevention Project (MPP). Results showed that both perceived peer and friend cigarette use predicted own cigarette use within and across the adolescent years. For own alcohol and marijuana use, peer and friend influences were limited primarily to middle school. The findings suggest that strategies for counteracting peer and friend influences should receive early emphasis in prevention programs that are targeted to middle school. The findings also raise the question of whether cigarette use may represent a symbol of peer group identity that is unlike other drug use, and once formed, may have lasting adverse effects through the adolescent years.