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Naltrexone Injection

Generic name: naltrexone (injection) [ nal-TREX-own ]
Brand name: Vivitrol
Dosage form: intramuscular powder for injection, extended release (380 mg)
Drug classes: Antidotes, Drugs used in alcohol dependence

Medically reviewed by Philip Thornton, DipPharm. Last updated on May 24, 2021.

What is naltrexone?

Naltrexone blocks the effects of opioid medication, including pain relief or feelings of well-being that can lead to opioid abuse. An opioid is sometimes called a narcotic. Vivitrol is used as part of a treatment program for drug or alcohol dependence.

Naltrexone injection is used to prevent relapse in adults who became dependent on opioid medicine and then stopped using it. Naltrexone can help keep you from feeling a "need" to use the opioid.

Naltrexone injection is also used to treat alcoholism by reducing your urge to drink alcohol. This may help you drink less or stop drinking altogether. You should not be drinking at the time you receive your first injection.

Naltrexone is not a permanent cure for drug addiction or alcoholism.


You should be treated with naltrexone only if you have not recently used: any opioid medicine, buprenorphine, methadone, or medicine to treat a cold, cough, diarrhea, or pain. Using these medicines in the 7 to 14 days before starting naltrexone can cause sudden opioid withdrawal symptoms.

Do not use opioid medication, heroin, or other street drugs while you are receiving this medicine. Doing so could result in dangerous effects, including coma and death.

Call your doctor if you have ongoing or worsening pain, redness, itching, bruising, swelling, or a hard lump where the medicine was injected.

Naltrexone can harm your liver. Tell your doctor if you have upper stomach pain, dark urine, or yellowing in the whites of your eyes.

After receiving naltrexone, your body will be more sensitive to opioids if you use an opioid medicine in the future. Using the same amount you used before could lead to overdose or death.

Before taking this medicine

You should not receive a naltrexone injection if you still use opioid medicine, or you could have sudden and severe withdrawal symptoms.

You should not be treated with naltrexone if you are allergic to it, or if:

  • you are currently addicted to opioids;

  • you are having withdrawal symptoms from opioid addiction;

  • you have used any opioid medicine within the past 7 to 14 days (including fentanyl, Vicodin, OxyContin, and many others);

  • you have used methadone or buprenorphine (Subutex, Butrans, Suboxone, Zubsolv) in the past 14 days; or

  • you have used any medicine to treat a cold, cough, diarrhea, or pain in the past 7 to 14 days.

To make sure naltrexone is safe for you, tell your doctor if you have ever had:

  • liver disease;

  • kidney disease; or

  • bleeding problems such as hemophilia.

Tell your doctor if you are pregnant or breastfeeding.

It is not known whether naltrexone will harm an unborn baby. However, if you use opioid medicine while you are pregnant, your baby could become dependent on the drug. This can cause life-threatening withdrawal symptoms in the baby after it is born. Babies born dependent on opioids may need medical treatment for several weeks.

How is naltrexone given?

Naltrexone is injected into a muscle. This injection is usually given once a month (every 4 weeks) and can be given only by a healthcare professional. Get your naltrexone injection regularly to get the most benefit.

You may notice pain, redness, itching, bruising, swelling, or a hard lump where the medicine was injected. Call your doctor if you have this type of reaction, especially if it gets worse or does not clear up within 2 weeks.

Naltrexone injections are only part of a complete treatment program that may also include additional forms of counseling and/or monitoring. Follow your doctor's instructions very closely.

In case of emergency, wear or carry medical identification to let others know you are using this medicine.

After using naltrexone, your body will be more sensitive to opioids. If you use an opioid medicine in the future, you will need to use less than before naltrexone treatment. Using the same amount you used before could lead to overdose or death.

Dosing information

Usual Adult Dose for Alcohol Dependence:

380 mg intramuscularly every 4 weeks/once a month

Usual Adult Dose for Opiate Addiction:

380 mg intramuscularly every 4 weeks/once a month

-There is no data specifically addressing switching from buprenorphine or methadone to naltrexone, however some patients have reported severe manifestations of precipitated withdrawal when switched from an opioid agonist to opioid antagonist therapy.
-Patients switching from buprenorphine or methadone may be vulnerable to precipitated withdrawal for up to 2 weeks.
-Be prepared to manage withdrawal symptomatically with non-opioid medications.
-This drug is of value only as a part of a comprehensive management plan that includes measures to ensure the patient takes this medication.

Use(s): Blockade of the effects of exogenously administered opioids

What happens if I miss a dose?

Call your doctor for instructions if you miss an appointment for your injection.

What happens if I overdose?

Since this injection is given by a healthcare professional in a medical setting, an overdose is unlikely to occur. However, overdose symptoms may include nausea, stomach pain, drowsiness, dizziness, or a reaction where an injection was given (such as severe pain or skin changes).

What should I avoid while using naltrexone?

Do not use opioid medication, heroin, or other street drugs while you are receiving naltrexone. Once naltrexone is injected, it cannot be removed from your body. Never try to overcome the effects of naltrexone by taking large doses of opioids. Doing so could result in dangerous effects, including coma and death.

Ask your doctor before using any medicine to treat a cold, cough, diarrhea, or pain. These medicines may contain opioids and may not work as well while you are using this medicine.

Avoid driving or hazardous activity until you know how this medicine will affect you. Dizziness or drowsiness can cause falls, accidents, or severe injuries.

Naltrexone side effects

Get emergency medical help if you have signs of an allergic reaction to naltrexone: hives; chest pain, wheezing, difficult breathing; feeling light-headed; swelling of your face, lips, tongue, or throat.

Using opioid medicine while you are receiving this medicine could stimulate opioid withdrawal symptoms. Common withdrawal symptoms are yawning, sweating, fever, stomach pain, vomiting, diarrhea, watery eyes, runny nose, goose bumps, body aches, shaking, muscle twitching, trouble sleeping, and feeling restless or anxious.

Call your doctor at once if you have:

  • weak or shallow breathing;

  • new or worsening cough, wheezing, trouble breathing;

  • severe pain, swelling, blistering, skin changes, a dark scab, or a hard lump where the medicine was injected;

  • liver problems - stomach pain (upper right side), dark urine, tiredness, jaundice (yellowing of the skin or eyes); or

  • symptoms of depression - unusual mood or behavior changes, loss of interest in things you once enjoyed, crying, new sleep problems, thoughts about hurting yourself.

You may feel nauseated the first time you receive this medicine. You may also have a headache, tiredness, joint and muscle pain, loss of appetite, and vomiting.

Common naltrexone side effects may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect naltrexone?

Other drugs may interact with naltrexone, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Alternatives to naltrexone

There are alternative drugs in different forms available to treat opioid use disorder.

Talk with your healthcare provider which option would be best suited to you.

Medicines used to treat opioid addiction:


Buprenorphine and naloxone



For opioid overdose in an emergency situation:


Other Medicines used to treat alcohol addiction:

  • Campral
  • Antabuse

Other related medicines:

Buprenorphine for severe pain:

Popular FAQ

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

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

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

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

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Further information

  • Your doctor can provide more information about naltrexone.

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use naltrexone only for the indication prescribed.

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