Prescription medicine
Methylnaltrexone Brand names: Relistor
Methylnaltrexone (Relistor) is a prescription medicine with an FDA approval on record since 2008. No generic is listed in FDA's NDC Directory.
- No generic listed
Check it at the source: the methylnaltrexone FDA label on DailyMed (effective May 1, 2024, Salix Pharmaceuticals, Inc.); the NDA 21964 record on Drugs@FDA; every methylnaltrexone label on DailyMed.
Highlights of the record
FDA label of May 1, 2024; NDC Directory, Drugs@FDA and Orange Book, October 8, 2026
Used for
From the label: indications and usageRELISTOR is an opioid antagonist.
Forms and strengths
- 150 mg
- 8 mg/.4ml
- 12 mg/.6ml
Injection (solution); tablet.
On the market
- Earliest approval on file
- April 24, 2008 Relistor, Salix Pharms; Drugs@FDA’s file, where older or withdrawn approvals can be missing
- Generic approvals
- 2 first August 26, 2024; 0 with a marketed status in Drugs@FDA
- Labelers listed (NDC)
- 1 of which 0 under generic applications, 1 under brand applications, repackagers included
- Last listed patent
- December 31, 2030 Relistor injection; not a generic launch date
Supply and safety
- Pharmacy cost (NADAC)
- Not in the survey
- Shortage (FDA)
- No current entry
- Recalls by its makers (FDA)
- No recall recorded
- FAERS reports
- 1,497 through July 30, 2026
What is methylnaltrexone used for?
From the label: indications and usageRELISTOR is an opioid antagonist. RELISTOR tablets and RELISTOR injection are indicated for the treatment of opioid-induced constipation (OIC) in adults with chronic non-cancer pain, including patients with chronic pain related to prior cancer or its treatment who do not require frequent (e.g., weekly) opioid dosage escalation. ( 1.1 )
RELISTOR injection is indicated for the treatment of OIC in adults with advanced illness or pain caused by active cancer who require opioid dosage escalation for palliative care. […]
FDA pharmacologic class: Opioid Antagonist.
Source: FDA drug label (Relistor), Salix Pharmaceuticals, Inc., effective May 1, 2024 (SPL set c488fb7c-0a5b-487c-b452-996809d1cb99), via openFDA; the full label on DailyMed
What does the patient leaflet for methylnaltrexone say first?
The FDA-approved Medication Guide or Patient Information that comes with the medicine, in its own words.
From the patient leaflet: What is the most important information I should know about RELISTOR?RELISTOR can cause serious side effects, including: • Tear in your stomach or intestinal wall (perforation). Stomach pain that is severe can be a sign of a serious medical condition. If you get stomach pain that is severe, does not go away, or gets worse, stop taking RELISTOR and get emergency medical help right away. • Diarrhea that is severe or that will not go away. Stop taking RELISTOR and call your healthcare provider if you get diarrhea that is severe or that does not go away during treatment with RELISTOR. • Opioid withdrawal. You may have symptoms of opioid withdrawal during treatment with RELISTOR including sweating, chills, diarrhea, stomach pain, anxiety, and yawning. Tell your healthcare provider if you have any of these symptoms.
From the patient leaflet: How should I store RELISTOR?RELISTOR tablets: • Store RELISTOR tablets at room temperature between 68° to 77°F (20° to 25°C). • The bottle of RELISTOR tablets contains 2 desiccant canisters to help keep your medicine dry. Do not remove the desiccant canisters from the bottle. RELISTOR injection (Vials and Pre-filled Syringes): • Store RELISTOR vials and pre-filled syringes at room temperature between 68° to 77°F (20° to 25°C). • Do not freeze RELISTOR vials or pre-filled syringes. • Keep RELISTOR vials and pre-filled syringes away from light until you are ready to use them. • If the contents of a RELISTOR vial have been drawn into a syringe and you are not able to use the medicine right away, keep the syringe at room temperature for up to 24 hours. Keep RELISTOR and all medicines, needles and syringes out of the reach of children.
Source: FDA drug label (Relistor), Salix Pharmaceuticals, Inc., effective May 1, 2024 (SPL set c488fb7c-0a5b-487c-b452-996809d1cb99), via openFDA; the full label on DailyMed
Is there a generic for methylnaltrexone (Relistor)?
The FDA approved the first generic methylnaltrexone on August 26, 2024. 2 generic applications are approved; 0 of them carry a current (not discontinued) marketing status in Drugs@FDA; that status is not evidence that the generic is on sale. Drugs@FDA also holds 1 tentative approval: the FDA found the generic approvable, but patents or exclusivity keep it from final approval for now.
The Orange Book lists 6 patents for Relistor injection, the last expiring on December 31, 2030; a patent listed only for Relistor tablets runs to March 10, 2031. A patent or exclusivity date is not the date a generic goes on sale: court cases and settlements move it either way.
- 2008 earliest approval on file
- 2024 first generic approved
- 2030 last listed patent
Source: Drugs@FDA, FDA NDC Directory and the Orange Book (openFDA bulk files, October 8, 2026)
What does the methylnaltrexone label say about other medicines?
The methylnaltrexone label names 1 other medicine in its interaction, contraindication or warning sections. The sentences are the labels' own; a label lists what its studies and reports found, not every interaction.
| Medicine named | Section | What the label says |
|---|---|---|
| Dextromethorphan | drug interactions | Metabolized by Cytochrome P450 Isozymes In healthy subjects, a subcutaneous dose of 0.3 mg/kg of RELISTOR did not significantly affect the metabolism of dextromethorphan, a CYP2D6 substrate. |
Source: FDA drug label (Relistor), Salix Pharmaceuticals, Inc., effective May 1, 2024 (SPL set c488fb7c-0a5b-487c-b452-996809d1cb99), via openFDA; the full label on DailyMed
What do FAERS reports show for methylnaltrexone?
The FDA Adverse Event Reporting System holds 1,497 reports that list methylnaltrexone among the medicines taken, through July 30, 2026, each a report of something that happened, not proof the medicine caused it; 332 are coded as a death and 339 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is.
Reports received each year
The most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026
What next?
- Other opioid antagonists
- the pharmacologic class, with prices and generics
- Methylnaltrexone side effects
- the label's list beside FAERS reports
- Check an interaction
- what two or more labels say about each other