The mechanisms underlying the interaction of the A118G SNP and the potential benefits of naltrexone in alcohol dependence are unknown. It is thought that the effect of naltrexone is mediated by its ability to block the elevations in β-endorphin induced by alcohol administration, which are thought to contribute to the subsequent euphoria. Indeed, it has been shown that naltrexone has a greater propensity to block alcohol-induced highs in individuals with the G118 allele (Ray and Hutchison, 2007), which may, in part, explain the reduction in rates of relapse. In contrast, it was shown that the urge to drink following naltrexone treatment was greater in G118 allele-carriers (McGeary et al., 2006). However, it should be noted that in this study, conducted in non-treatment seekers, the urge to drink was evaluated following exposure to alcohol cues rather than alcohol administration.
