The relative importance of perceived substance misuse use by different peers on smoking, alcohol and illicit drug use in adolescence.

BACKGROUND: Substance use by young people is strongly associated with that of their peers. Little is known about the influence of different types of peers. We tested the relationship between perceived substance use by five types of peers and adolescents' use of illicit drugs, smoking, and alcohol consumption. METHODS: We used data collected from 1285 students aged 12-13 as part of a pilot cluster randomized controlled trial (United Kingdom, 2014-2016). The exposures were the perceived use of illicit drugs, smoking and alcohol consumption by best friends, boy or girlfriends, brothers or sisters, friends outside of school and online. Outcomes were self-reported lifetime use of illicit drugs, smoking and alcohol consumption assessed 18-months later. RESULTS: The lifetime prevalence of illicit drug use, smoking and alcohol consumption at the 18-month follow-up were 14.3%, 24.9% and 54.1%, respectively. In the fully adjusted models, perceived substance use by friends outside of school, brothers or sisters, and online had the most consistent associations with outcomes. Perceived use by friends online was associated with an increased risk of ever having used illicit drugs (odds ratio [OR] = 2.43, 95% confidence interval [CI] = 1.26, 4.69), smoking (OR = 1.61, 95% CI 0.96, 2.70) and alcohol consumption (OR = 2.98, 95% CI = 1.71, 5.18). CONCLUSIONS: Perceived substance use by friends outside of school, brothers and sisters and online could be viable sources of peer influence. If these findings are replicated, a greater emphasis should be made in interventions to mitigate the influence of these peers