List of products in the National Drug Code with proprietary name . This medication is used to prevent people who have been addicted to certain drugs (opiates) from taking them again. It is used as part of a complete treatment program for drug abuse (e.g., compliance monitoring, counseling, behavioral contract, lifestyle changes). This medication must not be used in people currently taking opiates, including methadone. Doing so can cause sudden withdrawal symptoms. Naltrexone belongs to a class of drugs known as opiate antagonists. It works in the brain to prevent opiate effects (e.g., feelings of well-being, pain relief). It also decreases the desire to take opiates. This medication is also used to treat alcohol abuse. It can help people drink less alcohol or stop drinking altogether. It also decreases the desire to drink alcohol when used with a treatment program that includes counseling, support, and lifestyle changes.