Adolescent Sibling Associations among Alcohol, Cannabis, and Sexual Risk Behavior: A Test of Interdependence.

BACKGROUND:Although siblings are conceptualized as a salient social influence during adolescence, few studies have examined how adolescent siblings influence each other's substance use and risky sexual behavior. Objectives: In this study, we investigated the influence of alcohol use days, cannabis use days, and cannabis and alcohol co-use days on the sexual risk behavior of siblings while accounting for dyadic influence. METHODS:At the baseline visit for a randomized controlled trial for adolescents referred due to parents' concerns about their substance use ("referred adolescents"; n = 99; Mage=15.95; 38.38% female), we assessed alcohol and cannabis use days as well as sexual risk behavior of the referred adolescents and their sibling (Mage=15.03; 51.52% female). We computed the number of days in the 30 days prior to the baseline that alcohol and cannabis use occurred on the same day. Using a cross-sectional actor partner interdependence model, we tested two models of how adolescents' substance use is associated with their own ("actor effect") and their siblings' ("partner effect") sexual risk behavior-one model for alcohol and cannabis use, and one model for daily co-use. RESULTS:For referred adolescents and their siblings, within an individual, greater alcohol, cannabis, and daily co-use was significantly associated with sexual risk behavior (actor effects). Furthermore, more sibling co-use days was positively associated with referred adolescent sexual risk behavior (partner effect), representing interdependence. CONCLUSION:These findings confirm the influence siblings have on one another's risky behavior in adolescence and have implications for prevention and intervention efforts for adolescent substance use.