One of the more therapeutically relevant findings regarding the A118G SNP is in the treatment of alcoholism. It was discovered that individuals carrying the G118 allele were more likely to respond positively to naltrexone treatment (Oslin et al., 2003). In this study, there were 3.5 times more naltrexone-treated G118 allele-carriers, compared with A118 allele-carriers, who did not relapse to heavy drinking. There were no differences in rates of abstinence, suggesting that individuals with the G118 allele may better handle alcohol exposure without fully relapsing to heavy drinking. There were no differences between genotypes for those receiving placebo treatments, demonstrating that the benefit of the G118 allele is specific for naltrexone treatment and does not confer an enhanced ability for the individual to refrain from relapse. Subsequent studies investigating the involvement of this SNP in naltrexone response have replicated these initial findings (Anton et al., 2008; Kim et al., 2009; Oroszi et al., 2009; Oslin et al., 2003). For instance, using a haplotype-based approach, the A118G locus, and not SNPs found in the same haplotype block, contributed to the improved response
