The study consists of 12 weeks of outpatient treatment with 50mg/day of naltrexone or placebo. Up to 340 subjects will be recruited across four sites. The inclusion criteria include adult males and females of European or Asian descent with DSM-IV diagnosis of alcohol dependence and heavy drinking per TLFB criteria. Patients with major psychiatric disorders or on psychotropic medications, other substance dependence problems (except nicotine), severe cognitive impairment, active suicidal/homicidal thoughts and serious medical conditions (including liver disorders) will be excluded.