Alcohol abuse and dependence represent a sizeable public health problem in the United States, with about 8.5% of the adult population diagnosed with either alcohol abuse or dependence in a given year (Grant et al., 2004). Treatment strategies for alcohol use disorders (AUDs) include the Food and Drug Administration-approved medication naltrexone, an opioid antagonist that has highest affinity for the mu-opioid receptor (Littleton and Zieglgansberger, 2003). Results from clinical trials have demonstrated moderate efficacy of naltrexone for alcohol dependence. Specifically, findings suggest that naltrexone treatment reduces the occurrence of heavy drinking days (Balldin et al., 2003, Monti et al., 2001, Rubio et al., 2002), increases time to first relapse (Anton et al., 1999, Guardia et al., 2002, Kiefer et al., 2003), and yields lower relapse rates (Heinala et al., 2001, Latt et al., 2002, Volpicelli et al., 1992). Additionally, naltrexone reduces the number of drinking days (O’Malley et al., 1992, Volpicelli et al., 1992) and the number of drinks per drinking episode (Chick et al., 2000, Guardia et al., 2002, Morris et al., 2001, O’Malley et al., 1992). Results from
