Naltrexone binds to the endorphin receptors in the body, and blocks the effects and feelings of alcohol. Naltrexone reduces alcohol cravings and the amount of alcohol consumed.  When these areas of the brain are blocked, you feel less need to drink alcohol, and you can stop drinking more easily.
Once a patient stops drinking, taking naltrexone helps patients maintain their sobriety.
Naltrexone does not make you feel sick if you drink alcohol while taking it, unlike disulfiram (brand name: Antabuse), another medicine that is sometimes used for alcoholism.