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Generic name: naltrexone, naltrexone hydrochloride
Brand name: Vivitrol
Dosage form: extended-release intramuscular injection (powder for suspension), oral tablet
Drug classes: Antidotes, Drugs used in alcohol dependence

Medically reviewed by Philip Thornton, DipPharm. Last updated on Apr 4, 2023.

What is naltrexone?

Naltrexone is a prescription medication used to treat alcohol use disorder and opioid use disorder. It helps you stop using these substances and remain off them.

Naltrexone belongs to a class of drugs known as opioid antagonists and works by blocking the mu opioid receptor. It blocks the effects of alcohol and opioid medications, preventing the intoxication these substances cause. Naltrexone also modifies how the hypothalamus, pituitary gland and adrenal gland (hypothalamic-pituitary-adrenal axis, HPA axis) interact to suppress the amount of alcohol consumed.

Naltrexone comes as an extended-release intramuscular injection (Vivitrol) and as oral tablets. The branded versions of naltrexone tablets (Revia, Depade) have been discontinued, but generic versions are available.

Naltrexone tablets were first approved by the US Food and Drug Administration (FDA) in 1984. In 2006, the FDA also approved Vivitrol, the extended-release intramuscular injection form of naltrexone.

What is naltrexone used for?

Naltrexone is a prescription medication that is used:

You should stop drinking alcohol or using opioids before starting naltrexone.

Naltrexone hydrochloride should not be used in children and adolescents under 18 years.

Important information

Naltrexone can cause serious side effects, including:

1. Risk of opioid overdose.

You can accidentally overdose in two ways.

2. Severe reactions at the site of the naltrexone injection (injection site reactions).

Some people have had severe injection site reactions, including tissue death (necrosis), while receiving naltrexone injections. Some of these injection site reactions have required surgery. This medication must be injected by a healthcare provider. Call your healthcare provider right away if you notice any of the following at any of your injection sites:

Tell your healthcare provider about any reaction at an injection site that concerns you, gets worse over time, or does not get better by two weeks after the injection.

3. Sudden opioid withdrawal.

Anyone who receives naltrexone must not use any type of opioid (must be opioid-free) including street drugs, prescription pain medicines, cough, cold, or diarrhea medicines that contain opioids, or opioid dependence treatments, buprenorphine or methadone, for at least 7 to 14 days before starting this medication. Using opioids in the 7 to 14 days before you start receiving treatment may cause you to suddenly have symptoms of opioid withdrawal when you receive treatment. Sudden opioid withdrawal can be severe, and you may need to go to the hospital.

You must be opioid-free before receiving naltrexone unless your healthcare provider decides that you don't need to go through detox first. Instead, your doctor may decide to give this medication in a medical facility that can treat you for sudden opioid withdrawal.

4. Liver damage or hepatitis. Naltrexone can cause liver damage or hepatitis.

Tell your healthcare provider if you have any of the following symptoms of liver problems during treatment with this medication:

Your healthcare provider may need to stop treating you with this medication if you get signs or symptoms of a serious liver problem.

You must inform every doctor that treats you that you are taking Naltrexone. Non-opiate based anesthetics should be used if you require an anesthetic in an emergency situation. If you have to use opiate containing anesthetics, you may need higher doses than usual. You may also be more sensitive to the side-effects (breathing difficulties and circulatory problems).

Who should not use naltrexone?

Do not use naltrexone if you:

What should I tell my doctor before using naltrexone?

Before you receive naltrexone, tell your healthcare provider if you:

How should I use naltrexone?

Using opioids in the 7 to 14 days before you start receiving naltrexone may cause you to suddenly have symptoms of opioid withdrawal. To avoid this you should not use opioids for a minimum of 7-10 days before starting treatment with naltrexone.

How to take naltrexone tablets

How you will receive a naltrexone injection

Whenever you need medical treatment, be sure to tell the treating healthcare provider that you are receiving this medication and mention when you got your last dose. This is important because naltrexone can also block the effects of opioid-containing medicines that might be prescribed for you for pain, cough or colds, or diarrhea.

Carry written information with you at all times to alert healthcare providers that you are taking this medication so that they can treat you properly in an emergency. Ask your healthcare provider how you can get a wallet card to carry with you.

What happens if I miss a dose?

If you forget to take your naltrexone tablet, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take a double dose to make up for a forgotten dose.

If you miss your appointment for your naltrexone injection, schedule another appointment as soon as possible.

What happens if I overdose?

If you take more naltrexone tablets than you should, tell your Doctor or Pharmacist or contact your nearest hospital emergency department immediately.

What should I avoid while using naltrexone?

Do not drive a car, operate machinery, or do other dangerous activities until you know how this medication affects you. Naltrexone may make you feel dizzy and sleepy.

Dosing information


Intramuscular injection:

See the full prescribing information for further details about naltrexone dosing.

What are the side effects of naltrexone?

Serious side effects of naltrexone include:

Common side effects of naltrexone include:

Tell your healthcare provider if you have any side effect that bothers you or that does not go away.

These are not all the side effects of this medication. For more information, ask your healthcare provider or pharmacist.

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


Tell your healthcare provider about all the medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements.

Especially tell your healthcare provider if you take any opioid-containing medicines for pain, cough or colds, or diarrhea.

If you are being treated for alcohol dependence but also use or are addicted to opioid-containing medicines or opioid street drugs, it is important that you tell your healthcare provider before starting naltrexone to avoid having sudden opioid withdrawal symptoms when you start treatment.

Know the medicines you take. Keep a list of them to show your healthcare provider and pharmacist when you get a new medicine.

Pregnancy and breastfeeding

Tell your doctor if you are pregnant or plan to become pregnant. It is not known if naltrexone will harm your unborn baby. This medication should only be used during pregnancy if the potential benefits justifies the potential risk to the fetus.

Tell your doctor if you are breastfeeding. It is not known if naltrexone passes into your milk when it is administered by IM injection, and it is not known if it can harm your baby. Naltrexone from tablets passes into breast milk. Talk to your healthcare provider about whether you will breastfeed or take this medication. You should not do both.


Keep out of sight and reach of children.

What are the ingredients in naltrexone?

Active ingredient: naltrexone (injection), naltrexone hydrochloride (tablets)

Inactive ingredients:

Vivitrol brand injection: polylactide-co-glycolide (PLG). Diluent ingredients: carboxymethylcellulose sodium, polysorbate 20, sodium chloride, sodium hydroxide and hydrochloric acid as pH adjusters, in water for injection.

Tablets (Chartwell): lactose monohydrate, hypromellose, magnesium stearate, polyethylene glycol, titanium dioxide, colloidal silicon dioxide, hydroxypropyl cellulose, yellow ferric oxide and red ferric oxide.

Inactive ingredients vary among the different generic tablet formulations of naltrexone. Check the product label for your particular formulation for a complete list of inactive ingredients.

The Vivitrol brand of naltrexone injection is manufactured and marketed by Alkermes, Inc. 852 Winter Street, Waltham, MA 02451-1420. A number of different companies manufacture and market generic tablet formulations of this medication.

Popular FAQ

Low dose naltrexone means taking a dose of naltrexone that is up to one-tenth, or 10%, of the dose that is usually taken for opioid addiction. A low dose of naltrexone is approximately 4.5mg of naltrexone a day compared with the usual dosage of naltrexone for opioid addiction which is 50mg to 100mg a day. Continue reading

Naltrexone blocks the feelings of intoxication (the “buzz”) from alcohol when you drink it. This allows people with alcohol use disorder to lessen their drinking behaviors enough to stay in treatment, avoid relapses, and take their medication. Over time, cravings for alcohol will decrease. However, naltrexone will not prevent you from becoming impaired while drinking alcohol. Do not use naltrexone so that you can drive or perform other activities under the influence of alcohol. Continue reading

Do NOT take opiates, including heroin or other prescription or illegal opiates while using naltrexone. Taking opiates with naltrexone increases your risk for an overdose, coma and death. Do not use naltrexone if you are dependent on opioids or if you are experiencing opioid withdrawal symptoms. Naltrexone should not be used before you complete a medically-supervised opioid withdrawal lasting at least 7 to 14 days. Continue reading

The manufacturer does not specify if you should take naltrexone tablets in the morning or at night. Take naltrexone exactly as your doctor orders it. Many patients take their medication in the morning to help affirm their continued treatment success for either opioid use disorder or alcohol use disorder. Taking naltrexone tablets after a meal (for example: breakfast) may help to lessen any stomach side effects such as nausea or pain. Continue reading

Weight gain is not a common side effect with oral naltrexone treatment. When used in combination with bupropion, naltrexone is approved to help promote weight loss. Naltrexone is known to frequently cause stomach side effects like nausea and vomiting, stomach pain or cramping, and loss of appetite which could contribute to weight loss. Weight gain and increased appetite have been reported as a possible side effect, but is not common. Continue reading

Acamprosate and naltrexone are two different medications that are used in the treatment of alcohol use disorder. They work in different ways to help people who are dependent on alcohol to abstain from drinking it. Naltrexone is also used for the treatment of opioid use disorder.

Acamprosate was thought to be slightly more effective at helping people with alcohol use disorder remain off alcohol, while naltrexone was thought to be slightly more effective at helping reduce heavy drinking and cravings, according to the results of a meta-analysis which used data from 64 trials.

Results from two small studies, however, indicate that naltrexone is more effective than acamprosate in a number of areas. Continue reading

When taken as directed, naltrexone may reduce your cravings for alcohol or opioids. You’ll feel less of a need to take drugs or drink. Continue reading

Oral naltrexone is well absorbed and will usually begin working within one hour after a dose. Intramuscular naltrexone is an extended-release formulation and has two peaks, first at 2 hours then again 2 to 3 days later, although its therapeutic effect lasts for one month Continue reading

Naltrexone is a pure opiate receptor antagonist and works by primarily binding at the mu opioid receptors. By binding to these receptors, it blocks the euphoric (pleasurable or "high") effects linked with alcohol use or opioids. Continue reading

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.