Twin and family studies have consistently found that cannabis use and use disorders appear to in part have a genetic basis [for review see Agrawal and Lynskey, 2006]. Studies that have evaluated the role of genetic and environmental risk factors on cannabis abuse or cannabis dependence in twin samples have found estimates of heritability that range from 0.45 to 0.78 [see Kendler and Prescott, 1998; Tsuang et al., 1998; van den Bree et al., 1998; Maes et al., 1999; Kendler et al., 2000, McGue et al., 2000; Miles et al., 2001; Rhee et al., 2003]. Taken together, these studies suggest that there are substantial heritable influences on cannabis use disorders and that studies aimed at identifying genes that contribute to cannabis involvement may be warranted.
