Methylnaltrexone
Methylnaltrexone is a peripherally-acting mu-opioid receptor antagonist used to treat opioid-induced constipation in patients with advanced illness. By selectively blocking opioid receptors in the gastrointestinal tract without crossing the blood-brain barrier, it helps restore bowel function while preserving central analgesic effects.
Methylnaltrexone is a peripherally-acting opioid antagonist that treats opioid-induced constipation by blocking mu-opioid receptors in the gut.
Key facts at a glance
- RxNorm
- 29899
- Generic
- Methylnaltrexone
- Class
- unclassified
- Brands
- Relistor
- Availability
- rx
- Lactation
- unknown
- Routes
- oral
- Forms
- prefilled syringe, injection, tablet
- Regions
- US, EU, CN, JP
- Monitoring
- —
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Treatment of opioid-induced constipation in patients with advanced illness who are receiving palliative care, when response to laxative therapy has been insufficient.
As a selective mu-opioid receptor antagonist with quaternary amine structure, methylnaltrexone cannot cross the blood-brain barrier, allowing it to block peripheral opioid receptors in the gastrointestinal tract while preserving central analgesic effects.
Contraindicated in patients with known or suspected gastrointestinal obstruction. Should be discontinued if opioid analgesia is discontinued. Use with caution in patients with impaired renal or hepatic function. May cause symptoms such as abdominal pain, diarrhea, or flatulence.
Official drug label
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This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed July 26, 2026. · Read our editorial policy