The consistency of family and peer influences on the development of substance use in adolescence.

Latent growth modeling (LGM) was used to analyse longitudinal data for adolescent substance use from five overlapping age cohorts (11, 12, 13, 14, and 15 years at first assessment) measured at four annual time points. An associative cohort-sequential model was tested for alcohol, cigarette and marijuana use with a sample of 345 adolescents (11-18 years old) from an urban area in the Pacific Northwestern region of the United States. Hypotheses concerning the shape of the growth curve, the extent of individual differences in the common trajectory over time, and the influence of family cohesion, peer encouragement and gender on initial substance use and shape of the growth curve were tested. Results indicated similarities between alcohol, cigarette and marijuana initial use and development, with peer encouragement and family cohesion predictive of initial levels of use, and changes in peer encouragement influencing the developmental trajectories of the three substances. Females were higher than males in initial status and developed less rapidly in their use of the substances than did males. Findings are discussed in terms of the similarities and differences in the developmental trajectories of the three substances and the importance of family and peer influences on these trends.