Treatment Impacted Polymorphism Effect of Polymorphism References NRT:         CYP2A6*1B Increased nicotine metabolism. Reduced NRT success [165-168]   COMTrs4680 Reduced COMT activity. Increased NRT efficacy. [171,172]   CHRNA5-CHRNA3-CHRNA4 Alterations in nAChR activity. Altered responsiveness to NRT. May also impact craving and withdrawal. [173-175]   DRD2-141C Ins/Del Altered dopamine receptor expression. Del C allele associated with increased NRT efficacy. [38,176]   DRD4 VNTR Reduced likelihood of abstinence at 12 weeks. [177] Varenicline:         CHRNA5-CHRNA3-CHRNA4 Variation in varenicline response. Nausea with varenicline treatment. [182]   CHRNB2 Nausea with varenicline treatment. [183] Bupropion:         CYP2B6*6 Increased bupropion efficacy in smoking cessation. [64]   DRD4exon III VNTR Increased bupropion efficacy in smoking cessation. [189]   DRD2-141C Ins/Del Increased bupropion smoking quit rates with Del C allele. [176]   SLC6A3/SLC6A4 Altered dopamine transporter activity. Altered bupropion efficacy in smoking cessation. [190-194] Nortriptyline:         SLC6A4 Altered dopamine transporter activity. Increased nortriptyline efficacy with high activity variants. [192-195] CB1 Antagonists:         DRD2 A1 Increased efficacy of rimonabant in smoking cessation [198-200]

Table 2: Genetic polymorphisms impacting smoking cessation therapies.