Naltrexone, a broad opioid-receptor antagonist, was the first medication since disulfiram to be approved by the United States of America Food and Drug Administration for the treatment of alcohol dependence. In the initial clinical trials in the early 1990s, oral naltrexone, 50 mg, was shown to significantly reduce the risk of relapsing to heavy drinking compared to placebo. These early trials were followed by other trials throughout the world such that by 2010 about 4,000 individuals had been studied. Meta-analyses of these trials revealed that oral naltrexone is effective in reducing relapse to heavy drinking but less effective in enhancing abstinence. The effect size is modest, in the .15 to .2 range, which has impacted the adoption of naltrexone use by clinicians. Intramuscular versions of naltrexone active for one month have also shown efficacy. The tolerability of naltrexone is reasonable with the most common side-effect being nausea. Hepatotoxicity with naltrexone has not emerged as a clinical problem at the standard 50 mg dose though at higher doses hepatoxicity is of concern. The length of treatment with naltrexone has not been well studied though many clinicians recommend one year of treatment. Efforts are underway to identify predictors of naltrexone response but, to date, no predictor has achieved clinical utility. It is anticipated that the role of naltrexone and other opioid antagonists in the treatment of alcohol dependence will continue to be refined and that this class of medications will come to be seen as an important option in the clinical care of the patient with alcohol dependence.