Relistor is a drug that people use to treat constipation that opioid medications can cause. Relistor is effective because it does so without reducing the pain-relieving effects of the opioid drugs.

People who have severe pain might receive a prescription for opioid medications from their doctor. However, these opioids can cause severe constipation in some individuals. This happens because they work by binding to opioid receptors in both the central nervous system and the gut.

A person taking opioid medication may stop using the pain relief because the constipation causes so much discomfort. As a result, the severe pain then returns.

Relistor, also known as methylnaltrexone bromide, can help people in this situation.

In this article, we explain how Relistor works, its effectiveness, and possible risks of using this drug.

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Relistor helps reduce opioid-induced constipation.

Opioids, such as morphine, stop pain by numbing pain receptors in the brain. However, they also numb the receptors in the digestive tract.

Numbness in the digestive system means that the muscles do not move undigested food and stools toward the rectum.

The slower the food moves through the digestive tract, the more water the colon absorbs from the food. The feces then become dry and hard.

Meanwhile, contractions occur in the middle of the small intestine but do not push the food forward. The digestive system secretes fewer fluids, the urge to defecate reduces, and constipation results.

Relistor, or methylnaltrexone bromide, blocks the numbing effects of opioids in the intestines. The drug binds to the receptors in the gut, blocking morphine’s effects on them, and so they are no longer numb. This means that the muscles in the gut can process feces normally once more.

Relistor does not enter the brain, so morphine continues to enact a painkilling effect. If the drug was to enter the brain, it would cancel out morphine’s painkilling effects, leaving the individual in pain again.

Methylnaltrexone is a highly effective medicine.

One 2016 study found that 45.9 percent of people taking methylnaltrexone experienced a rescue-free bowel movement within 4 hours of the first dose. By the fifth week of taking the drug, around 70 percent of participants experienced three or more rescue-free bowel movements per week.

A 2017 open-label trial also found that the only adverse effects presenting in people taking the drug for 48 weeks were nausea, abdominal pain, and diarrhea, and these were only mild to moderate. In this trial, 34.1 percent of injections elicited a bowel movement within 4 hours.

Some common side effects of Relistor include:

People might also find that they sweat more than usual after taking Relistor.

Adverse effects are unlikely, and very few people cease taking the medication due to the severity of side effects.

However, people who have a gastrointestinal blockage should not take Relistor.

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Scientists developed Relistor to treat opioid-induced constipation without taking away from the pain-relieving effect of opioid medication.

In 1978, colleagues at the University of Chicago started looking for ways to help people who would not take morphine for pain due to unbearable constipation. They wanted to find a medication that would treat the constipation without reducing the painkilling effects of the opioid.

Lead researcher Dr. Leon Goldberg noticed that medications, including loperamide, were already available that acted on the opioid receptors of the digestive system without crossing into the brain.

The team started screening compounds in its search for a drug that would relieve constipation without entering the brain and neutralizing morphine’s painkilling effects.

A compound called N-methyl-naltrexone (MNTX), that the German pharmaceutical company Boehringer Ingelheim made, was promising.

In 2005, following tests, two pharmaceutical companies signed an agreement to develop the drug and sell methylnaltrexone.

The new drug would treat opioid-induced side effects, including constipation and postoperative ileus. In this condition, a part of the intestine becomes paralyzed, and the stomach muscles cannot push food forward. Postoperative ileus might occur after abdominal surgery.

The Food and Drug Administration (FDA) approved Relistor for the treatment of opioid-induced constipation in 2008.


Are there any natural alternatives to Relistor for people with opioid-induced constipation?


Drink plenty of fluids, remain as active as possible, don’t delay going to the bathroom when the urge occurs, and increase intake of fibrous fruits and vegetables. If bowel movements become more difficult, adding daily doses of a herbal extract called senna may help.

Alan Carter, PharmD Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.
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