Naltrexone Mylan 50 mg is a type of medicine called an opioid antagonist. It is mainly used to treat alcoholism and the use of opioids. This medicine helps you to stop using these substances and remain off them. Naltrexone Mylan 50 mg belongs to a group of drugs known as opioid antagonists. The way it works is by blocking the mu opioid receptor. It blocks out the effects of alcohol and opioid medications, preventing intoxication these substances cause.