Associations between CNR1 and substance misuse have also not been consistently replicated. The (AAT)n variant has been linked with cocaine, heroin, alcohol and polysubstance abuse (Ballon et al., 2006; Comings et al., 1997; Johnson et al., 1997). However, these reports differed regarding the number of (AAT)n repeats that is associated with drug misuse risk. Although the majority of studies examining CNR1 SNPs reported significant associations with substance misuse, no uniform patterns of associations with specific SNPs have emerged (Agrawal et al., 2009; Chen et al., 2008; Hopfer et al., 2006; Hutchison et al., 2008; Schmidt et al., 2002; Zhang et al., 2004; Zuo, Kranzler, Luo, Covault, & Gelernter, 2007). Other investigators have failed to find significant relationships between substance use and (AAT)n tandem repeat (Covault, Gelernter, & Kranzler, 2001; Heller, Schneider, Seifert, Cimander, & Stuhrmann, 2001; Li et al., 2000; 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
