Research demonstrates a genetic component in the etiology of substance use and misuse in both sexes (McGue et al. 1992; van den Bree et al. 1998; Kendler et al. 1999, 2000; Agrawal & Lynskey, 2008). However, heritabilities tend to be greater in adult males compared to adult females for substance misuse (Sivkis et al. 1994; van den Bree et al. 1998; Li et al. 2003). Environmental variables such as peer group and family dysfunctions also play a role (Petraitis et al. 1995), particularly at younger ages. In contrast to adults, however, a sex difference in etiology has not been exhibited in adolescence (McGue et al. 2000; Rhee et al. 2003). The results of this research are intriguing and suggest that genetic factors are important in adulthood, shared environmental factors are important at younger ages, and sex differences in these factors are only found in adulthood. Longitudinal twin designs have supported this (Koopmans et al. 1997; Viken et al. 1999; White et al. 2003; Malone et al. 2004; Hicks et al. 2007; Kendler et al. 2008a,b,c) but no study has examined sex differences in this developmental process.
