What is naltrexone?

Quick Answer
Naltrexone is a medication prescribed for the treatment of alcohol and opiate use disorders.
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How Does Naltrexone Work?

Naltrexone is an antagonist that binds to the mu (µ) opioid receptors in the brain but does not stimulate them. This is important because naltrexone is used to treat addictions, but like some addiction medications, it does not result in euphoria. When used with psychosocial therapy, naltrexone has been shown to be an effective adjunct for the treatment of addiction disorders.

Once naltrexone has reached a therapeutic level in the patient’s system (in as little as a few hours), a couple of processes occur. First, there is typically a significant drop in cravings for the drug, and second, if opiates (such as heroin, morphine, and buprenorphine) or alcohol are used, no euphoria is experienced. Naltrexone blocks the activation of the receptors of the dopamine that is typically released when opiates or alcohol are consumed: No dopamine, no euphoria.

Furthermore, because these receptors are accustomed to being stimulated, a lack of dopamine results in more cravings. With naltrexone occupying those receptors, cravings are decreased significantly. The decrease in cravings, coupled with the loss of the euphoria experienced when drinking or using opiates, may dramatically reduce the chances of relapse and provide the patient with the extra assistance needed to participate in psychosocial treatment. It must be noted that because naltrexone will remove any chemical currently occupying the receptor, symptoms of withdrawal will follow. Because of this, the patient must be free of opiates before being given naltrexone.

Side effects of naltrexone include nausea, headache, dizziness, anxiety, fatigue, and trouble sleeping. Hepatotoxicity, or chemical-induced liver damage, has been found when naltrexone is given in excessive doses. The specificity and intensity of the side effects may depend on the form in which the medication is taken.

Drug Forms

Naltrexone is prescribed in two different forms—oral (ReVia or Depade) and in an intramuscular injection (Vivitrol). ReVia is typically prescribed in a 50 milligram dose, once daily. Reactions to oral naltrexone vary. Some patients have reported side effects severe enough to discontinue use. However, frequency of side effects is greatly reduced with the once-monthly injectable form of naltrexone.


Naltrexone has been shown to have positive, albeit varied results. Some research indicates that patients on naltrexone report significant reductions in their average drinking days and in heavy drinking days (more than four to five drinks per day). Other research indicates positive treatment outcomes in the areas of retention, compliance, and group therapy attendance. However, other studies report some problems with medication adherence.


Naltrexone in either form (oral or injection) is contraindicated for anyone with active hepatitis, liver failure, or severe liver disease. In addition, anyone who is actively taking opiates (either illicitly or for pain) should not take naltrexone because it will negate any opiate-based effects (for example, pain reduction or management). Additional contraindications may depend on the form of the medication.


AHFS Consumer Medication Information. “Naltrexone.” MedlinePlus. US Natl. Lib. of Medicine, Feb. 2009. Web. 29 Oct. 2015.

Gihyun Yoon, Suck Won Kim, Paul Thuras, and Joseph Westermeyer. “Safety, Tolerability, and Feasibility of High-Dose Naltrexone in Alcohol Dependence: An Open-Label Study.” Human Psychopharmacology: Clinical and Experimental 26.2 (2011): 125–32. Print.

Lobmaier, Philipp P., Nikolaj Kunøe, Michael Gossop, and Helge Waal. “Naltrexone Depot Formulations for Opioid and Alcohol Dependence: A Systematic Review.” CNS Neuroscience and Therapeutics 17.6 (2011): 629–36. Print.

“Naltrexone for Alcoholism.” FamilyDoctor.org. Amer. Acad. of Family Physicians, May 2014. Web. 29 Oct. 2015.

Substance Abuse and Mental Health Services Administration. The Facts about Naltrexone. Rockville: US Dept. of Health and Human Services, 2012. PDF file.