The CYP2B6*6 haplotype is defined as having both the Q172H and K262R variants and is the most common CYP2B6 haplotype (Lee et al. 2007). Smokers carrying the CYP2B6*6 genotype exhibited greater quitting success with bupropion compared to placebo at the end of treatment and 6-month follow-up. However, the genotype by treatment interaction was driven by differential quit rates by genotype on placebo; the two genotype groups had equivalent quit rates on bupropion suggesting that this association may be mediated by nicotine metabolism rather than bupropion metabolism (Lee et al. 2007). Recently, several CYP2B6 polymorphisms were associated with abstinence among treatment-seeking smokers randomized to bupropion therapy (King et al. 2011), although their function is not known.
