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Naltrexone Injection

Generic Name: naltrexone (injection) (nal TREX own)
Brand Name: Vivitrol

Medically reviewed by Philip Thornton, DipPharm. Last updated on Sep 28, 2020.

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.

Naltrexone is an injectable medicine used as part of a treatment program for drug or alcohol dependence.

Naltrexone injection is used to prevent relapse in people 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. This medicine will not decrease the effects of alcohol you recently consumed. You should not be drinking at the time you receive your first injection.

Naltrexone is not a cure for drug addiction or alcoholism.

Important Information

If you are addicted to pain drugs and are given naltrexone injection, you may have experience precipitated withdrawal.

You should not receive naltrexone if you are having drug or alcohol withdrawal symptoms, if you have taken any opioid medicine within the past 2 weeks, or if you are still actively drinking alcohol.

Avoid driving and doing other tasks or actions that call for you to be alert until you see how naltrexone injection affects you.

Naltrexone may affect certain lab tests. Tell all of your health care providers and lab workers that you use this injection.

People using naltrexone injection to keep a drug-free state may get more effects from pain drugs when the injection is stopped. Even low doses of pain drugs may cause very bad and sometimes deadly effects in these people.

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 receive naltrexone if you are allergic to it, or if:

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

  • liver disease;

  • kidney disease; or

  • a bleeding or blood-clotting disorder such as hemophilia.

It is not known whether naltrexone will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

Naltrexone can pass into breast milk and may harm a nursing baby. You should not breast-feed while using this medicine.

How is naltrexone used?

Naltrexone is injected into a muscle. This injection is usually given once a month (every 4 weeks) and can be given only by a doctor or nurse in a clinic.

It is important to receive your naltrexone regularly to get the most benefit.

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

Wear a medical alert tag or carry an ID card stating that you use naltrexone. Any medical care provider who treats you should know that you are receiving this medication. If you need surgery, tell the surgeon ahead of time that you are receiving this medicine.

After receiving naltrexone, your body will be more sensitive to opioids. If you use an opioid medicine in the future, you will need to use a lower dose than before you started treatment with this medicine. Using the same amount you used before could lead to overdose or death.

What happens if I miss a dose?

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

Naltrexone dosing information

Usual Adult Dose for Alcohol Dependence:

Average dose: 50 mg orally once a day
Duration of therapy: 12 weeks

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.
-To achieve best possible results, implement compliance-enhancing techniques, especially medication compliance

Usual Adult Dose for Opiate Dependence:

Initial dose: 25 mg orally once a day
Maintenance dose: 50 mg orally once a day (if no withdrawals on 25 mg/day)

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 overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while using naltrexone?

Do not use narcotic medication, heroin, or other street drugs while you are receiving naltrexone. 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.

Do not drink alcohol during treatment with naltrexone.

Ask your doctor before using any medicine to treat a cold, cough, diarrhea, or pain. These medicines may contain narcotics or alcohol.

Naltrexone may impair your thinking or reactions. Avoid driving or operating machinery until you know how this medicine will affect you.

Naltrexone side effects

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

Using opioid medicine while you are receiving naltrexone injections could stimulate opioid withdrawal symptoms. Common withdrawal symptoms are yawning, irritability, sweating, fever, chills, shaking, vomiting, diarrhea, watery eyes, runny nose, goose bumps, body aches, trouble sleeping, and feeling restless.

Call your doctor at once if you have:

  • weak or shallow breathing;

  • confusion, severe dizziness, feeling like you might pass out;

  • depression, thoughts about suicide or hurting yourself;

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

  • new or worsening cough, wheezing, trouble breathing; or

  • liver problems - nausea, upper stomach pain, itching, tired feeling, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Common naltrexone side effects may include:

  • nausea, vomiting, changes in appetite;

  • muscle cramps;

  • dizziness, drowsiness;

  • abnormal liver function tests;

  • sleep problems (insomnia);

  • stuffy nose, tooth pain; or

  • pain, swelling, or itching where the injection was given.

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?

Naltrexone will block the effects of any narcotic medicines you take (such as prescription medicine for pain, cough, or diarrhea). Harmful side effects could also occur.

Other drugs may interact with naltrexone, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.

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.

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

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

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

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 not classified as a controlled substance. It's a full opioid antagonist that blocks euphoric actions at the opioid receptor (meaning it can't lead to a "high" or addiction).
It is used as one part of the treatment plan of patients with alcohol dependence or opioid use disorder, along with counseling. Continue reading

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