Naltrexone was well-tolerated, as the rate of adverse events was low, and safe, as it did not interfere with the normalization of biochemical markers of heavy drinking or alter liver function markers. Naltrexone seemed to reduce relapse rate to heavy drinking, but we found no differences in other alcohol consumption variables between naltrexone- and placebo-treated groups. Although the naltrexone group showed a tendency to consume fewer drinks per drinking day and had a longer time to first drink, differences were not statistically significant.