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What Is Naltrexone?

What Is Naltrexone?

Intramuscular extended release naltrexone is a medication approved by the Food and Drug Administration (FDA) to treat both opioid use disorder (OUD) and alcohol use disorder (AUD). Naltrexone can be prescribed and administered by any practitioner licensed to prescribe medications and is available in a pill form for AUD or as an extended-release intramuscular injectable for AUD and OUD. The pill form can be taken daily for AUD, but the extended-release injectable formulation is approved for the treatment of OUD. The pill form is taken daily and the extended-release injectable is administered every four weeks, or once a month, by a practitioner.

Naltrexone is one component of a comprehensive treatment plan, which includes counseling and other behavioral health therapies to provide patients with a whole-person approach. Naltrexone is not a recommended option for anyone younger than 18 years of age, or for patients experiencing other health conditions.

How Does Naltrexone Work?

Naltrexone is not an opioid, is not addictive, and does not cause withdrawal symptoms with stop of use. Naltrexone blocks the euphoric and sedative effects of opioids such as heroin, morphine, and codeine. Naltrexone binds and blocks opioid receptors and reduces and suppresses opioid cravings. There is no abuse and diversion potential with naltrexone.

Naltrexone for Opioid Use Disorder

To reduce the risk of withdrawal symptoms caused by OUD, patients should wait at least 7 days after their last use of short-acting opioids and 10 to 14 days for long-acting opioids, before starting naltrexone.

Patients taking naltrexone should not use any other opioids or illicit drugs; drink alcohol; or take sedatives, tranquilizers, or other drugs. Patients should notify their practitioner about all medications they are currently taking as well as any changes in medications while being treated with naltrexone.

While the oral formulation will also block opioid receptors, only the long-acting injectable formulation is FDA approved as a medication for OUD.

Patients on naltrexone, who discontinue use or relapse after a period of abstinence, may have a reduced tolerance to opioids. Therefore, taking the same, or even lower doses of opioids used in the past can cause life-threatening consequences.

SAMHSA funds the Providers Clinical Support System – Medications for Opioid Use Disorders (PCSS-MOUD) to provide free training and mentoring to medical practitioners to identify and treat opioid use disorder.

Naltrexone for Alcohol Use Disorder

When starting naltrexone for AUD, patients must not be physically dependent on alcohol or other substances. To avoid strong side effects such as nausea and vomiting, practitioners typically wait until after the alcohol detox process before administering naltrexone.

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. Once a patient stops drinking, taking naltrexone helps patients maintain their sobriety. Naltrexone treatment lasts for three to four months. Practitioners should continue to monitor patients who are no longer taking naltrexone.

SAMHSA funds the Providers Clinical Support System – Medications for Alcohol Use Disorders (PCSS-MAUD) to provide free training and mentoring to medical practitioners to identify and treat alcohol use disorder.

Naltrexone Safety Precautions

Patients should talk to their practitioner before starting treatment with naltrexone about the following situations:

  • Current liver problems, use illegal drugs, have hemophilia or other bleeding problems, have kidney problems, or have any other medical conditions
  • Are pregnant, plan to become pregnant, or are breastfeeding
  • All medications, prescriptions and non-prescription medicines, vitamins, and herbal supplement
  • It is important for practitioners to know if patients are currently taking any opioid-containing medicines for pain, cough, colds, or diarrhea
  • Currently being treated for an OUD or AUD
  • Are allergic to naltrexone or any of the ingredients or the liquid used to mix the extended-release naltrexone

Common and Serious Side Effects of Naltrexone

These are not all the side effects of naltrexone. For more information, patients should talk to their practitioner or pharmacist. Patients should tell their practitioner about any side effects that are bothersome or do not go away.

Patients and practitioners are encouraged to report all side effects online to MEDWatch, FDA’s medical product safety reporting program for health care professionals, patients, and consumers, or by calling 1-800-FDA-1088.

Common side effects may include:

Common side effects may include:

  • nausea
  • sleepiness
  • headache
  • dizziness
  • vomiting
  • decreased appetite
  • painful joints
  • muscle cramps
  • cold symptoms
  • trouble sleeping
  • toothache
Serious side effects may include:

Serious side effects of Naltrexone may include:

  • Severe reactions at the site of injection, including: intense pain; tissue death for which surgery may be required; swelling, lumps, or hardness; scabs, blisters, or open wounds
  • Liver damage or hepatitis, including; stomach area pain lasting more than a few days; dark urine; yellowing of the whites of your eyes; tiredness
  • Serious allergic reactions, including: skin rash; swelling of face, eyes, mouth, or tongue; trouble breathing or wheezing; chest pain; feeling dizzy or faint
  • Pneumonia
  • Depressed mood
Risk of Opioid Overdose

What are the Risks of an Opioid Overdose?

Patients should tell family and the people they are closest to about the increased sensitivity to opioids and the risk of overdose.

Accidental overdose can happen in two ways:

  • Naltrexone blocks the effects of opioids, such as heroin or opioid pain medicines. Patients who try to overcome this blocking effect by taking large amounts of opioids may experience serious injury, coma, or death.
  • After receiving a dose of naltrexone, the blocking effect slowly decreases and completely goes away over time. Patients who are taking naltrexone for an OUD can become more sensitive to the effects of opioids at the dose used before, or even lower amounts. Using opioids while on naltrexone can lead to overdose and death.

Patients should not take naltrexone if they:

  • Currently use or have a physical dependence on opioid-containing medicines or opioid drugs, such as heroin, or currently experiencing opioid withdrawal symptoms
  • Experience opioid withdrawal symptoms. Withdrawal symptoms may happen when a patient was taking opioid-containing medicines or opioid drugs regularly and then stopped.
  • Symptoms of opioid withdrawal may include: anxiety, sleeplessness, yawning, fever, sweating, teary eyes, runny nose, goose bumps, shakiness, hot or cold flushes, muscle aches, muscle twitches, restlessness, nausea and vomiting, diarrhea, or stomach cramps.

Dispose of unused naltrexone safely. Talk to your physician for guidance, or for more information on the safe disposal of unused medications, visit FDA's disposal of unused medicines or DEA's drug disposal webpages.

Resources and Publications

Tip 63: Medications for Opioid Use Disorder (2021) Banner

Tip 63: Medications for Opioid Use Disorder (2021)

This Treatment Improvement Protocol reviews the use of the three FDA-approved medications used to treat OUD.

Clinical Use of Extended-Release Injectable Naltrexone in the Treatment of OUD (2014) pdf

Clinical Use of Extended-Release Injectable Naltrexone in the Treatment of OUD (2014)

This brief guide explains how to use extended-release injectable naltrexone as part of Medications for Opioid Use Disorder (MOUD).

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Contact Information

Opioid Treatment Program Contacts
For information about other Medications for Opioid Use Disorder (MOUD) or the certification of opioid treatment programs (OTPs), contact the SAMHSA Division of Pharmacologic Therapies at 240-276-2700 or DPT@SAMHSA.HHS.Gov. For assistance with the Opioid Treatment Program Extranet, contact the OTP helpdesk at 1-866-348-5741 or

Provider Support Contacts
For general information, providers can contact SAMHSA's Center for Substance Abuse Treatment (CSAT) at 1-866-287-2728 or email

Last Updated
Last Updated: 03/29/2024
Last Updated