What are the Different Naltrexone Side Effects?

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  • Written By: Laura M. Sands
  • Edited By: Heather Bailey
  • Last Modified Date: 07 October 2018
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Naltrexone side effects may include gastrointestinal upset, headache, sleep disturbances and a host of other uncomfortable symptoms. More serious side effects from this drug may include breathing difficulties and difficulty swallowing. Although commonly used for opioid addiction, in studies where its effectiveness for fibromyalgia has been tested using very low doses, only a few very minor naltrexone side effects have been reported.

Naltrexone is often used to treat individuals addicted to opiates by blocking the effects of these drugs on the brain. In many instances, it may also help considerably reduce the craving for drugs. Naltrexone side effects tend to be very slight when used for opioid addiction, but they do exist. Perhaps one of the most alarming naltrexone side effects is the liver function abnormalities it sometimes causes.

The most common naltrexone side effects tend to be minor and include upset stomach, nausea, diarrhea and vomiting. Some may also experience an increase in headaches while taking the drug or experience muscle or joint pain. These symptoms are often easy to relieve with the use of over-the-counter medications.


More severe naltrexone side effects may indicate liver damage and require immediate medical attention. These include severe abdominal pain, yellowing skin or eyes and dark urine. Other severe naltrexone side effects include difficulty breathing, coughing, facial swelling and tongue and throat swelling, as well as problems swallowing. In some people, this drug may also cause allergic pneumonia. Pain, inflammation, itching and redness on the skin where the medication was injected may also signal an allergic reaction to the drug.

When taken orally, doctors recommend that naltrexone always be taken with food to avoid unwelcomed stomach upset. Dizziness is sometimes reported as a side effect of this drug, as is blurred vision and fainting. Side effects may also be experienced if naltrexone is taken with other drugs, such as codeine, methadone or morphine. Doctors recommend that individuals taking naltrexone avoid harmful interactions by carrying medical information on them at all times to alert emergency personnel that naltrexone is being used.

Low dose naltrexone side effects on clinical trial participants who have taken the drug for possible fibromyalgia treatment are almost nonexistent. Occasionally, participants have experienced graphic dreams. Actual physical side effects similar to those sometimes experienced in patients taking higher doses for opioid addiction do not appear to be a factor, however.



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