A growing body of research indicates that siblings have marked influence on adolescents’ alcohol and other substance use. Results from genetically informed designs reveal that concordance between siblings in these domains exceeds the influence of shared genetics and shared environments, including parenting, suggesting that sibling similarities arise via some form of social influence. Despite strong evidence that siblings are unique socializers of substance use, research on the mechanisms driving these associations is underdeveloped. There is a critical need to identify those processes that influence adolescents’ decisions regarding substance use. The lack of mechanistic understanding precludes informed development of family-based behavioral intervention strategies.

Thus, rooted in ecological and family systems frameworks, we propose an integrative theoretical framework of sibling influence and identify the micro- and global-social influence processes that account for sibling similarities and differences. Additionally, taking a developmental perspective, we will identify the dual trajectories and reciprocal associations between older and younger siblings’ substance use behaviors and related cognitions from early through late adolescence. This advance is critical, as previous work has only considered top-down (i.e., older to younger sibling) socialization. Testing ecological principles, we will also investigate the degree to which community characteristics moderate the influence of sibling socialization and youth’s substance use more generally.