COMT has been investigated for association with chronic stimulant drug phenotypes. The val allele has been associated with polysubstance abuse (Vandenbergh et al. 1997), and in a later case–control study, Li et al. (2004) found that the val/val genotype was significantly associated methamphetamine abuse. In addition, Lohoff et al. (2008) found that cocaine-dependent individuals possessed the lower activity met allele more often than controls, suggesting that this polymorphism may play some role in dependence. These results differ from the Vandenbergh et al. (1997) and Li et al. (2004) studies described above; Lohoff et al. suggest their finding of the met allele association may also be due to linkage disequilibrium or population stratification.
