Relistor Side Effects

Generic Name: methylnaltrexone

Note: This page contains side effects data for the generic drug methylnaltrexone. It is possible that some of the dosage forms included below may not apply to the brand name Relistor.

It is possible that some side effects of Relistor may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

Applies to methylnaltrexone: subcutaneous solution

As well as its needed effects, methylnaltrexone (the active ingredient contained in Relistor) may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking methylnaltrexone, check with your doctor immediately:

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

If any of the following symptoms of overdose occur while taking methylnaltrexone, get emergency help immediately:

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

Some methylnaltrexone side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned 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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