Reviewed on 8/30/2022

What Is Naltrexone and How Does It Work?

Naltrexone is used to prevent people who have been addicted to certain drugs (opiates) from taking them again. It is used as part of a complete treatment program for drug abuse (e.g., compliance monitoring, counseling, behavioral contract, lifestyle changes). This medication must not be used in people currently taking opiates, including methadone. Doing so can cause sudden withdrawal symptoms.

Naltrexone belongs to a class of drugs known as opiate antagonists. It works in the brain to prevent opiate effects (e.g., feelings of well-being, pain relief).

It also decreases the desire to take opiates.

Naltrexone is also used to treat alcohol abuse. It can help people drink less alcohol or stop drinking altogether. It also decreases the desire to drink alcohol when used with a treatment program that includes counseling, support, and lifestyle changes.

Naltrexone is available under the following different brand names: ReVia, Vivitrol, and Depade.

Dosages of Naltrexone

Dosage Forms & Strengths


  • 50 mg

Microspheres for IM injection

  • 380 mg

Dosage Considerations – Should be Given as Follows:

Opioid Dependence

  • Prevention of relapse after opioid detoxification; to be used only after patient has been opioid-free for 7-10 days and after negative naloxone challenge (no symptom withdrawal after naloxone administration)
  • Oral: 25 mg initially, then observation for 1 hour, then 50 mg once daily starting on day 2; flexible dosing regimens can be employed to accommodate patient convenience or ensure compliance
  • Intramuscular (IM): 380 mg in gluteal muscle every 4 weeks for maintenance of abstinence

Alcohol Dependence

  • Treatment in patients who have been able to abstain from alcohol in outpatient settings before treatment initiation
  • Oral: 50 mg once daily for up to 12 weeks
  • Intramuscular (IM): 380 mg in gluteal muscle every 4 weeks for maintenance of abstinence

What Are Side Effects Associated with Using Naltrexone?

Common side effects of naltrexone include:

  • Injection site reactions (includes bruising, induration, nodules, pain, itching, swelling, tenderness)
  • Nausea
  • Headache
  • Decreased appetite
  • Insomnia
  • Vomiting
  • Diarrhea
  • Dizziness
  • Upper respiratory tract infection (URTI)
  • Anxiety
  • Joint pain
  • Increased creatine phosphokinase
  • Sore throat
  • Depression
  • Muscle cramps
  • Back pain
  • Rash
  • Dry mouth
  • Sleepiness
  • Increased aspartate aminotransferase (AST)

Less common side effects of naltrexone include:

  • Hair loss
  • Shortness of breath
  • Swelling (edema)
  • Liver injury
  • Increased systolic and diastolic blood pressures
  • Liver function abnormalities
  • Labored breathing
  • Nonspecific electrocardiographic (ECG) changes
  • Opiate withdrawal (mild to severe signs and symptoms, including drug craving, confusion, drowsiness, visual hallucinations, abdominal pain, vomiting, diarrhea)
  • Palpitations
  • Phlebitis
  • Fast heart rate

Seek medical care or call 911 at once if you have the following serious side effects:

  • Severe headache, confusion, slurred speech, arm or leg weakness, trouble walking, loss of coordination, feeling unsteady, very stiff muscles, high fever, profuse sweating, or tremors;
  • Serious eye symptoms such as sudden vision loss, blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights;
  • Serious heart symptoms such as fast, irregular, or pounding heartbeats; fluttering in your chest; shortness of breath; and sudden dizziness, lightheartedness, or passing out.

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

What Other Drugs Interact with Naltrexone?

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist. Check with your physician if you have health questions or concerns.

What Are Warnings and Precautions for Naltrexone?


  • This medication contains naltrexone. Do not take ReVia, Vivitrol, or Depade if you are allergic to naltrexone or any ingredients contained in this drug
  • Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately


  • Patients who are on opioid analgesics, are opioid-dependent (e.g., opioid agonists [methadone], opioid partial agonists [buprenorphine]), are in acute opioid withdrawal, have positive urine test for opioids, or fail to pass naloxone challenge
  • Hypersensitivity

Effects of Drug Abuse

  • No information available

Short-Term Effects

  • Injection may cause severe injection-site reactions (e.g., cellulitis, necrosis, hematoma)
  • See "What Are Side Effects Associated with Using Naltrexone?"

Long-Term Effects

  • See "What Are Side Effects Associated with Using Naltrexone?"


  • Depression, suicide, and suicidality cited in postmarketing reports; causal relation not demonstrated
  • Vulnerability to opioid overdose: Patients should be alerted that they may be more sensitive to opioids, even at lower doses, after discontinuance of naltrexone
  • Opioid withdrawal precipitated abruptly by administration of opioid antagonist to opioid-dependent patient may result in withdrawal syndrome severe enough to necessitate hospitalization
  • Risk of hepatotoxicity with increasing doses; dose related hepatocellular injury; discontinue therapy if signs/symptoms of acute hepatitis develop
  • Injection may cause severe injection-site reactions (e.g., cellulitis, necrosis, hematoma)
  • Injectable microspheres are for intramuscular (IM) use only; inadvertent subcutaneous/intravenous (SC/IV) administration may increase risk of severe injection-site reactions
  • Cases of eosinophilic pneumonia reported; consider in patients with symptoms of progressive hypoxia and dyspnea
  • Use caution in patients with hepatic failure or with bleeding disorder including thrombocytopenia and hemophilia, or patients taking anticoagulant therapy; bleeding hematoma may occur from intramuscular (IM) administration
  • Use caution in renal impairment or hepatic impairment
  • Patients should be opioid free for a minimum of 7-10 days before initiating therapy; a naltrexone challenge test recommended to confirm opioid-free status

Pregnancy and Lactation

  • Use naltrexone with caution during pregnancy if benefits outweigh risks
  • Animal studies show risk and human studies are not available, or neither animal nor human studies were done
  • Naltrexone is excreted in breast milk; consult your doctor before breastfeeding

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