Placebo-controlled studies have demonstrated that patients treated with opioid antagonists had fewer drinking days, lower rates of resumed heavy drinking, and reduced alcohol craving, when compared with placebo-treated patients. Patients who received an opioid antagonist were also less likely to drink heavily if they sampled alcohol during treatment. One study also demonstrated that patients who were treated with the opioid antagonist naltrexone had lower serum aspartate aminotransferase and alanine aminotransferase levels than placebo-treated patients. This is consistent with self-reported decreases in alcohol consumption. These patients also had less severe alcohol-related problems than placebo-treated patients, as indicated by the Addiction Severity Index. Opioid antagonists might act by reducing the reinforcing effects of alcohol and the incentive to drink. These agents, when combined with comprehensive treatment programmes, are an effective adjunctive treatment for alcohol-dependent patients.