Relistor Side Effects

Generic Name: methylnaltrexone

Note: This document contains side effect information about methylnaltrexone. Some of the dosage forms listed on this page may not apply to the brand name Relistor.

Some side effects of Relistor may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

For the Consumer

Applies to methylnaltrexone: subcutaneous solution

Along with its needed effects, methylnaltrexone (the active ingredient contained in Relistor) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking methylnaltrexone:

More common
  • Diarrhea
  • increased sweating
Incidence not known
  • Bloody, black, or tarry stools
  • heartburn
  • indigestion
  • nausea
  • severe abdominal or stomach pain, cramping, or burning
  • trouble breathing
  • vomiting of material that looks like coffee grounds, severe and continuing

Get emergency help immediately if any of the following symptoms of overdose occur while taking methylnaltrexone:

Symptoms of overdose
  • Chills
  • cold sweats
  • confusion
  • dizziness, faintness, or lightheadedness when getting up from lying or sitting position

Some side effects of methylnaltrexone may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common
  • Bloated
  • dizziness
  • excess air or gas in the stomach or intestines
  • full feeling
  • passing gas
  • stomach pain

For Healthcare Professionals

Applies to methylnaltrexone: subcutaneous kit, subcutaneous solution


Gastrointestinal side effects including abdominal pain (28.5%), flatulence (13.3%), nausea (11.5%), and diarrhea (5.5%) have been reported.

Gastrointestinal side effects reported postmarketing have included rare cases of gastrointestinal (GI) perforation have been reported in advanced illness patients with conditions that may be associated with localized or diffuse reduction of structural integrity in the wall of the GI tract (i.e., cancer, peptic ulcer, Ogilvie's syndrome). Perforations have involved varying regions of the GI tract: (e.g., stomach, duodenum, colon). Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Nervous system

An 84-year-old male who was being treated for opioid-induced constipation experienced syncope coincident with methylnaltrexone (the active ingredient contained in Relistor) therapy. Methylnaltrexone 12.5 mg was withdrawn due to the syncope. The event, as assessed by the investigator as related to study medication.

Nervous system side effects including dizziness (7.3%) have been reported. Tremor, confusional state, and restlessness have been reported during a clinical trial. At least one patient experienced syncope during a clinical trial.


Dermatologic side effects have included increased hyperhidrosis.


Genitourinary side effects have included urinary retention during a clinical trial.


Other side effects have included rhinorrhea during a clinical trial.

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