revealed that among alcohol dependent patients treated with naltrexone, those with one or two copies of the G118 allele had better outcome (Oslin, Berrettini, Kranzler et al., 2003; Kim, Kim, Choi et al., 2009). Among individuals using transdermal nicotine for smoke cessation, those of the A/G and G/G genotype had better responses (Lerman, Wileyto, Patterson et al., 2004). Ramchandani, Umhau, Pavon et al. (2011) reported that alcohol intake induced dopamine release in carriers of the G118 allele, but not in A118 homozygotes. In addition, subjects with G118 allele needed higher morphine doses to attain adequate pain control for acute postoperative pain compared to those homozygous for the A118 allele subjects (Chou, Wang, Liu et al., 2006; Chou, Yang, Lu et al., 2006; Sia, Lim, Lim et al., 2008; Hayashida, Nagashima, Satoh et al., 2008; Campa, Gioia, Tomei et al., 2008). Studies on the role of G118 allele in alcohol or drug dependence have reported positive, negative, or no associations [for reviews, see (Kreek et al., 2005; Mague and Blendy, 2010)].
