Several studies examining the relative contributions of family and peer influences on adolescents’ alcohol and other substance use have indicated that the magnitude of sibling influences is greater than that of parental influences (Ary et al., 1993; Fagan and Najman, 2003; Windle et al., 2009) and is similarly important to the influences of peers (Brook et al. 1990; Needle et al. 1986). Twin studies have demonstrated that an interdependent sibling relationship (reliance on co-twin) is an important modifier of drinking habits, and it appears to reduce the impact of inherited liabilities on alcohol-related behavior especially in adolescence (Penninkilampi-Kerola et al., 2005). A study of Australian twins found that females with an older brother reported greater intoxication frequency and lifetime AUD symptoms (Ellingson et al., 2013). Previous work in FinnTwin12 found that twins from opposite-sex pairs were more likely to have initiated drinking at age 14 than age and cohort matched twins from same-sex pairs (Rose et al. 2001). Taken together, this literature suggests that aspects of the sibling relationship (e.g. sibling interdependence, opposite-sex sibling pairs) have effects on adolescent drinking.
