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Naltrexone Microspheres

Precautions

Before using naltrexone, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: current or recent use (in the last 7 to 14 days) of any type of opioid drug (such as morphine, methadone, buprenorphine), bleeding problems (such as hemophilia, low platelets), kidney disease, liver problems.

You should carry or wear medical identification stating that you are using this drug so that appropriate treatment can be given in a medical emergency.

This drug may make you dizzy or drowsy. Alcohol or marijuana (cannabis) can make you more dizzy or drowsy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. Avoid alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

After stopping naltrexone treatment or missing a dose of naltrexone, you may be more sensitive to lower doses of opioids, increasing your risk of serious, possibly fatal side effects from the opioid (such as decreased breathing, loss of consciousness). You may also be more sensitive to lower doses of opioids near the end of the month that you received naltrexone treatment.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

This medication blocks the effects of opiate drugs (including heroin) and similar drugs (opioids). However, large doses of heroin or opioids can overcome this block. Trying to overcome this block is very dangerous and may cause serious injury, loss of consciousness, and death. Make sure you completely understand and accept the risks and benefits of using this medication. Follow your doctor's instructions closely.

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

This drug passes into breast milk. Consult your doctor before breastfeeding.

Side Effects

Nausea, headache, dizziness, drowsiness, anxiety, tiredness, and loss of appetite may occur. If you have been using opiates regularly, mild opiate withdrawal symptoms may occur, including abdominal cramps, restlessness, bone/joint pain, muscle aches, and runny nose. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

Pain/redness/swelling/itching/bruising at the injection site may also occur. If any of these effects steadily worsen, or if they last longer than two weeks, tell your doctor or pharmacist right away. Rarely, a severe injection site reaction can cause permanent injury if not treated.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Sudden opiate withdrawal symptoms can occur within minutes after using naltrexone if you are physically addicted to opiates. Tell your doctor right away if any of these withdrawal symptoms occur: vomiting, diarrhea, mental/mood changes (such as anxiety, confusion, extreme sleepiness, visual hallucinations).

Tell your doctor right away if you have any serious side effects, including: fast/irregular heartbeat, depression/rare thoughts of suicide, signs of a serious breathing problem/pneumonia (such as cough, shortness of breath, wheezing), blisters/sores at injection site.

Get medical help right away if you have any very serious side effects, including: chest pain.

Naltrexone may rarely cause serious liver disease. The risk is increased when larger doses are used. Stop using this medication and get medical help right away if you have any symptoms of liver damage, including: dark urine, nausea/vomiting that doesn't stop, loss of appetite, stomach/abdominal pain, yellowing eyes/skin.

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

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RxAnswers™ is a copyrighted combined product from TraceGains and First DataBank, Inc.

Drug information is selected from data included with permission and copyrighted by First DataBank, Inc. This is a summary and does not contain all possible information about this product. For complete information about this product or your specific health needs, ask your healthcare professional. Always seek the advice of your healthcare professional if you have any questions about this product or your medical condition. This information is not intended as individual medical advice and does not substitute for the knowledge and judgment of your healthcare professional. This information does not contain any assurances that this product is safe, effective or appropriate for you.

This information is intended only for residents of the United States. Products sold under the same brand names in other countries may contain different ingredients.

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Information expires December 2025.