Naltrexone is a generic prescription drug used to treat certain substance use disorders. Naltrexone oral tablet does not come in any brand-name versions. This drug can cause mild to serious side effects, including sleep changes.

Naltrexone comes as an oral tablet. It’s used to treat alcohol use disorder and opioid use disorder in adults.

Keep reading to learn about common, mild, and serious side effects naltrexone can cause. For a general overview of the drug, including details about its uses, see this in-depth naltrexone article.

Below are just a few of the more common side effects reported by people taking naltrexone in studies. Side effects can vary depending on what condition the drug is being taken to treat.

More common side effects in people taking naltrexone for alcohol use disorder include:

More common side effects in people taking naltrexone for opioid use disorder include:

* To learn more about this side effect, see the “Naltrexone’s side effects explained” section.

Mild side effects have been reported with naltrexone. These include:

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist. And do not stop taking naltrexone unless your doctor recommends it.

Naltrexone may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

* To learn more about this side effect, see the “Naltrexone’s side effects explained” section.

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Serious side effects have been reported with naltrexone. These include:

If you develop serious side effects while taking naltrexone, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

* You should not start taking Naltrexone until you’ve been opioid-free for at least 7 to 10 days. Starting this medication before you’ve been sufficiently weaned from opioids increases your risk of severe withdrawal symptoms.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with naltrexone, visit MedWatch.

ALLERGIC REACTION

For some people, naltrexone can cause an allergic reaction. But this side effect wasn’t reported in the drug’s studies.

In general, symptoms of allergic reaction can be mild or serious.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should keep taking naltrexone.

If you have symptoms of a severe allergic reaction, such as swelling or difficulty breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to naltrexone, they may have you switch to a different treatment.

Get answers to some frequently asked questions about naltrexone’s side effects.

Are the side effects of low dose naltrexone different from those of higher doses?

Possibly, but this wasn’t specifically reported in the drug’s studies.

For alcohol use disorder and opioid use disorder, the usual dosage of naltrexone is 50 milligrams (mg) daily. But lower doses of naltrexone may be prescribed off-label for other uses. (With off-label use, doctors prescribe a drug for a purpose other than what it’s approved to treat.)

To learn more about possible side effects with low dose naltrexone, talk with your doctor or pharmacist. For details about naltrexone’s dosage, see this article.

Does naltrexone cause certain side effects when taken for weight loss?

Naltrexone is not approved for weight loss, so its prescribing information does not list side effects for this use.

If you have other questions about naltrexone’s side effects, talk with your doctor or pharmacist.

Do the side effects of naltrexone go away over time, or are they long term?

The side effects of naltrexone typically go away over time. In many cases, side effects such as dizziness and digestive problems go away within a few hours to days of starting naltrexone treatment. But how long side effects last can vary from person to person.

Long-term side effects with naltrexone are rare but possible. These may include liver problems or mood changes, such as depression.

Talk with your doctor or pharmacist to learn more about naltrexone’s side effects and how long they may last.

Help is out there

If you or someone you know is in crisis and considering suicide or self-harm, please seek support:

  • Call or text the 988 Suicide and Crisis Lifeline at 988 or chat at 988lifeline.org. Caring counselors are available to listen and provide free and confidential support 24/7.
  • Text HOME to the Crisis Text Line at 741741 to connect with a volunteer crisis counselor for free and confidential support 24/7.
  • Not in the United States? Find a helpline in your country with Befrienders Worldwide.
  • Call 911 or your local emergency services number if you feel safe to do so.

If you’re calling on behalf of someone else, stay with them until help arrives. You may remove weapons or substances that can cause harm if you can do so safely.

If you’re not in the same household, stay on the phone with them until help arrives.

Learn more about some of the side effects naltrexone may cause.

Digestive side effects

Digestive side effects were commonly reported in studies of naltrexone. These side effects may include:

  • abdominal pain or cramps
  • constipation
  • diarrhea
  • loss of appetite
  • nausea and vomiting

Keep in mind that digestive symptoms can also occur with opioid withdrawal. (Withdrawal refers to uncomfortable effects that can happen when you stop taking a drug your body is used to.) Taking naltrexone may lead to opioid withdrawal if you’ve taken an opioid within 10 days of starting treatment. To learn more about this risk, talk with your doctor.

What might help

If you have bothersome or long-lasting digestive side effects during naltrexone treatment, talk with your doctor. They can suggest ways to manage symptoms, such as nausea, constipation, and diarrhea.

Sleep changes

Sleep changes were a common side effect reported in studies of naltrexone. These may include insomnia and sleepiness.

What might help

If you notice sleep changes during naltrexone treatment, talk with your doctor. They can recommend ways to help manage your symptoms. You can also view this article for tips on developing healthy sleep habits.

Muscle and joint pain

Muscle pain and joint pain were common side effects reported in studies of naltrexone. These side effects may cause discomfort in various muscles or joints throughout your body.

What might help

If you have muscle or joint pain during naltrexone treatment, talk with your doctor. They may suggest over-the-counter pain relievers, such as ibuprofen (Advil, Motrin). They can also recommend other ways to help manage your symptoms.

Keeping track of side effects

During your naltrexone treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start a new drug or combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Sharing notes with your doctor will help them learn more about how naltrexone affects you. They can then use this information to adjust your treatment plan if needed.

Naltrexone can sometimes cause harmful effects in people with certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether naltrexone is a good treatment option for you.

Talk with your doctor about your health history before taking naltrexone. Be sure to tell them if any of the following factors apply to you:

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.