A few studies have reported associations of CYP2A6 with smoking cessation and response to treatment. Smokers with the null activity allele, CYP2A6*2, are twice as likely to quit smoking as smokers who do not possess that allele (Gu et al. 2000). Further, smokers with high activity alleles (CYP2A6*1/*1B) report more serious withdrawal symptoms during smoking cessation (Kubota et al. 2006). The correlation between CYP2A6 genotypes and withdrawal symptoms was more notable in smokers who used NRT, such as transdermal nicotine patch in which a high dose of nicotine is administered initially with a gradual decrease in dosage. Smokers with high CYP2A6 activity, treated with NRT, might maintain a low level of nicotine that desensitizes/inactivates a larger number of receptors than smokers with low activity.
