The Developmental Unfolding of Sibling Influences on Alcohol Use over Time.

Research has long demonstrated that siblings are similar in their alcohol use, however much of this work relies on cross-sectional samples or samples of adolescents alone and/or exclusive focus on older siblings' impact on younger siblings. Using a three time-point design from early adolescence to early adulthood (M ages = 14.9, 18.3, and 22.4 years, respectively; 55% female; 54% European ancestry, 38% Asian ancestry), we evaluated the prospective older and younger sibling influences on alcohol use across time (N = 613 sibling pairs; 35% sisters, 26% brothers, 39% mixed-gender; average age difference = 2.34 years; 34% full-biological siblings, 46% genetically-unrelated adopted siblings, 20% pairs where one child was the biological offspring of parents and the other was adopted). The results from both the traditional and random-intercept cross-lagged panel analyses showed that older siblings' alcohol use predicted younger siblings' alcohol use across each developmental transition and across a variety of sibling contexts (e.g., gender composition, age difference, genetic relatedness). On the other hand, younger siblings' alcohol use only predicted older siblings' alcohol use when siblings were close in age (1.5 years or less) and under conditions of high sibling companionship. These results add to a body of literature illustrating how both older and younger siblings are important socializing agents of adolescent and early adult alcohol use. Assessing or co-treating siblings for alcohol problems may be an important add-on to existing adolescent and early adult alcohol prevention and intervention programs.