Zhang et al., 2004) or with CNR1 SNPs (Heller et al., 2001; Herman, Kranzler, Cubells, Gelernter, & Covault, 2006). This conflicting literature may in part be related to differences in study samples (e.g. participants differed in the type and/or severity of illicit drug use, ancestry/ethnicity, etc.), high comorbidity of different illicit drugs within a given patient, as well as overlapping and specific genetic influences mediating each type of illicit drug misuse (Kendler, Jacobson, Prescott, & Neale, 2003; Tsuang et al., 1998; Young, Rhee, Stallings, Corley, & Hewitt, 2006).
