A more recent analysis from the first bupropion trial examined the role of the CYP2B6*6 variant on treatment response. Smokers with the CYP2B6*6 genotype (one or two copies of CYP2B6*6) performed poorly on placebo, but had a positive treatment response with bupropion (end-of-treatment quit rates of 14.3% on placebo vs. 32.5% on bupropion for this group), that was well-maintained at 6-month follow-up (12.9% on placebo vs. 31.2% on bupropion for this group). Those possessing the wild-type genotype had high quit rates regardless of treatment (31.6% on placebo vs. 31.0% on bupropion) (Lee et al., 2007a). Since the effect of genotype in this study was observed mainly in the placebo group, the CYP2B6*1 versus the CYP2B6*6 allele may exert their differing effects on relapse risk by altering brain metabolism of nicotine. This hypothesis is being explored in further investigations.
