The small number of pharmacogenetic studies analyzing the role of OPRM1 in nicotine dependence treatment have focused on the A118G polymorphism (Table 2). A clinical trial by Lerman et al. found that NRT patients carrying the G allele had better abstinence rates than A/A patients when treated with transdermal patches [77]. No effect of A118G was observed in patients receiving nasal spray treatments [77]. The effect of A118G on NRT efficacy was also observed in a multivariate analysis of another patient population [78]. However, a later trial in a British cohort found exactly the opposite association: patients with the A/A genotype were more likely to be abstinent when using transdermal patches [79]. A more recent trial found no effect of A118G genotype on NRT efficacy, although patients in the trial were treated with both transdermal patch and oral NRT, making a direct comparison difficult [80]. Since the original association was only found in transdermal patch efficacy, the addition of a second NRT type may be a confounding factor when directly comparing the findings to other studies. The contradictory findings of
