in the general population, genetic subgroups of individuals have been combined in some studies to represent those with variants associated with slow (less that 50% CYP2A6 activity), intermediate (80% CYP2A6 activity), and normal metabolism (100% CYP2A6 activity; Benowitz et al., 2006b). Included among the slow metabolizers are those who have one or two copies of the null (no activity) alleles (CYP2A6*2 or CYP2A6*4), or have two copies of the reduced activity alleles (CYP2A6*9 or CYP2A6*12). Intermediate metabolizers include carriers of a single CYP2A6*9 or CYP2A6*12 allele, and normal metabolizers are those with *1/*1 (wild-type genotypes). The population frequencies of the reduced activity alleles are 7–9% in Caucasians, 8% in African Americans, 16% in Chinese, 22% in Korean, and 21% in Japanese populations (Malaiyandi et al., 2005; Schoedel et al., 2004). The population frequencies of null alleles are 1.2% in Caucasians, 2% in African Americans, 7–15% in Chinese, 11% in Korean, and 20–24% in Japanese (Nakajima et al., 2006; Rao et al., 2000; Schoedel et al., 2004). The CYP2A6*1×2 allele is a duplication variant that is associated with higher rates of nicotine metabolism than the wild-type CYP2A6 (Rao et al., 2000). The CYP2A6*1B variant is associated with approximately a 20% higher
