Naltrexone is used along with counseling and social support to help people who have stopped drinking alcohol and using street drugs continue to avoid drinking or using drugs. Naltrexone should not be used to treat people who are still using street drugs or drinking large amounts of alcohol. Naltrexone is in a class of medications called opiate antagonists. It works by decreasing the craving for alcohol and blocking the effects of opiate medications and opioid street drugs.