Naltrexone is an opioid antagonist primarily used to treat alcohol use disorder and opioid dependence. It works by competitively binding to opioid receptors in the brain—especially the mu-opioid receptors—blocking the effects of opioids such as euphoria, respiratory depression, and cravings. This prevents opioid intoxication and reduces the desire to consume alcohol or opioids. Naltrexone does not produce addiction or withdrawal symptoms when used appropriately. It is available in oral and extended-release injectable forms and is used as part of comprehensive treatment that includes counseling and behavioral therapies.