Drug · FAERS side-effect profile with label screen

Methylnaltrexone side effects: what 1,497 FDA adverse event reports show

Methylnaltrexone Bromide · 39 reaction terms · 588 drug–reaction co-reports · data 2026-09-14

Drug class

Not stated in label

Label matched

Methylnaltrexone Bromide (Relistor)

closest FDA label found for this product string; brand list suppressed because the label is a related product, not an exact match

Who reports

1,497 reports · 60% serious · 332 with death outcome · 61% female

openFDA FAERS counts, all years, deduplication not applied

Used for

• RELISTOR 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.

FDA label, Indications and Usage

What it is

RELISTOR ® (methylnaltrexone bromide) is a mu-opioid receptor antagonist.

FDA label, Description section

Boxed warning

None in the current label

How to read this page. FAERS is a spontaneous-reporting system: counts are not incidence rates and a signal is not proof of causation. Each reaction below is run through an automated screen — is the term in the FDA label (known), in the indications (the disease being treated), an administrative/coding term, or none of these (unlabeled)? That screen is mechanical text matching, not a causality assessment. The 30 hand-written Bradford Hill assessments are on the causality assessment page. Not medical advice.

Causality screen of the 24 strongest signals

Labeled adverse reaction 1Labeled (related wording) 4Reporting / coding artifact 6Outcome field, not a reaction 1Not in label — unassessed 12

What the badges mean

Labeled adverse reaction The exact term appears in the label's warnings or adverse-reactions sections: a known, expected effect. The FAERS signal confirms the label rather than discovering anything.
Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
Outcome field, not a reaction Death is a report outcome, not a reaction term. It is dominated by the underlying illness; see the seriousness profile and the boxed warning instead.
Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.

Strongest disproportionality signals

Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 15 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.

Show: hide coding/lab/outcome terms hide indication terms unlabeled only hide PRR-only

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Inability to afford medication	19	27.1 17.3–42.4ROR 27.5 · χ² 451 / p 2e-100	26.4 EB05 17.9 · IC025 +3.2 3/3 methods agree	Not in label — unassessed	serious n=6	no trial data cached
Hospice care	16	22.8 14.0–37.1ROR 23.0 · χ² 311 / p 5e-70	22.2 EB05 14.3 · IC025 +2.9 3/3 methods agree	Not in label — unassessed	serious PRR 29.8	no trial data cached
Insurance issue	18	17.0 10.7–26.9ROR 17.2 · χ² 255 / p 1e-57	16.4 EB05 10.6 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious PRR 13.1	no trial data cached
Intestinal perforation	13	16.2 9.4–27.9ROR 16.4 · χ² 171 / p 3e-39	15.2 EB05 8.7 · IC025 +2.4 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 15.7	no trial data cached
Sleep apnoea syndrome	16	11.7 7.2–19.1ROR 11.8 · χ² 146 / p 5e-34	10.5 EB05 6.4 · IC025 +2.3 3/3 methods agree	Not in label — unassessed	serious PRR 13.4	no trial data cached
Muscle spasticity	10	11.3 6.1–21.0ROR 11.4 · χ² 84 / p 3e-20	9.2 EB05 4.8 · IC025 +1.8 3/3 methods agree	Not in label — unassessed	serious PRR 10.9	no trial data cached
Small intestinal obstruction	8	9.1 4.6–18.2ROR 9.2 · χ² 50 / p 7e-13	6.8 EB05 3.5 · IC025 +1.4 3/3 methods agree	Labeled (related wording) related wording	serious PRR 7.8	no trial data cached
Gastrointestinal pain	7	9.0 4.3–18.8ROR 9.0 · χ² 42 / p 5e-11	6.4 EB05 3.1 · IC025 +1.2 3/3 methods agree	Labeled (related wording) related wording	serious PRR 11.2	no trial data cached
Product packaging quantity issue	6	7.7 3.5–17.1ROR 7.7 · χ² 29 / p 4e-8	5.3 EB05 2.6 · IC025 +0.9 3/3 methods agree	Reporting / coding artifact	–	no trial data cached
Product use complaint	8	7.2 3.6–14.4ROR 7.3 · χ² 37 / p 6e-10	5.4 EB05 2.9 · IC025 +1.2 3/3 methods agree	Reporting / coding artifact	serious n=4	no trial data cached
Therapy interrupted	30	6.1 4.3–8.7ROR 6.2 · χ² 123 / p 7e-29	5.6 EB05 4.1 · IC025 +1.9 3/3 methods agree	Reporting / coding artifact	serious PRR 8.9 · 87% consumer	no trial data cached
Drug effect incomplete	16	6.1 3.7–9.9ROR 6.1 · χ² 63 / p 1e-15	5.3 EB05 3.4 · IC025 +1.6 3/3 methods agree	Reporting / coding artifact	serious PRR 2.9	no trial data cached
Muscle tightness	7	6.1 2.9–12.7ROR 6.1 · χ² 25 / p 3e-7	4.5 EB05 2.4 · IC025 +0.9 3/3 methods agree	Not in label — unassessed	serious PRR 11.3	no trial data cached
Hepatocellular injury	6	5.9 2.7–13.1ROR 5.9 · χ² 20 / p 4e-6	4.3 EB05 2.1 · IC025 +0.7 3/3 methods agree	Not in label — unassessed	serious PRR 5.7	no trial data cached
Withdrawal syndrome	17	5.6 3.5–9.1ROR 5.7 · χ² 60 / p 4e-15	4.9 EB05 3.3 · IC025 +1.5 3/3 methods agree	Labeled (related wording) related wording	serious PRR 1.8	no trial data cached
Hallucination, visual	8	5.3 2.7–10.7ROR 5.4 · χ² 24 / p 5e-7	4.2 EB05 2.3 · IC025 +0.9 3/3 methods agree	Not in label — unassessed	serious PRR 5.9	no trial data cached
Incorrect route of drug administration	13	5.0 2.9–8.6ROR 5.1 · χ² 38 / p 4e-10	4.3 EB05 2.7 · IC025 +1.2 3/3 methods agree	Reporting / coding artifact	serious PRR 5.6	no trial data cached
Needle issue	10	4.9 2.6–9.1ROR 4.9 · χ² 27 / p 9e-8	4.1 EB05 2.4 · IC025 +1.0 3/3 methods agree	Not in label — unassessed	serious n=6	no trial data cached
Syringe issue	6	4.8 2.2–10.7ROR 4.8 · χ² 14 / p 7e-5	3.7 EB05 1.9 · IC025 +0.5	Not in label — unassessed	serious n=2	no trial data cached
Drug withdrawal syndrome	29	4.6 3.2–6.6ROR 4.7 · χ² 78 / p 5e-19	4.3 EB05 3.1 · IC025 +1.5 3/3 methods agree	Labeled (related wording) related wording	serious PRR 3.4	no trial data cached
Death	243	4.0 3.5–4.4ROR 4.5 · χ² 556 / p 3e-123	3.9 EB05 3.5 · IC025 +1.8 3/3 methods agree	Outcome field, not a reaction	serious PRR 3.8	no trial data cached
Sedation	7	3.8 1.8–7.9ROR 3.8 · χ² 12 / p 3e-4	3.1 EB05 1.7 · IC025 +0.4	Not in label — unassessed	serious PRR 3.6	no trial data cached
Peritonitis	5	3.4 1.4–8.1ROR 3.4 · χ² 6 / p 0.006	2.8 EB05 1.3 · IC025 -0.1 PRR-only: not supported by EBGM or IC	Not in label — unassessed	serious PRR 3.3	no trial data cached
Expired product administered	8	3.4 1.7–6.7ROR 3.4 · χ² 11 / p 4e-4	2.9 EB05 1.6 · IC025 +0.4	Reporting / coding artifact	serious n=2	no trial data cached

Trial evidence (ClinicalTrials.gov)

Trial cross-check not yet run for this drug (ClinicalTrials.gov pull covers the 800 most-reported drugs first).

Most frequently reported reactions

By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Death	243	4.0 3.5–4.4ROR 4.5 · χ² 556 / p 3e-123	3.9 EB05 3.5 · IC025 +1.8 3/3 methods agree	Outcome field, not a reaction	serious PRR 3.8	no trial data cached
Therapy interrupted	30	6.1 4.3–8.7ROR 6.2 · χ² 123 / p 7e-29	5.6 EB05 4.1 · IC025 +1.9 3/3 methods agree	Reporting / coding artifact	serious PRR 8.9 · 87% consumer	no trial data cached
Drug withdrawal syndrome	29	4.6 3.2–6.6ROR 4.7 · χ² 78 / p 5e-19	4.3 EB05 3.1 · IC025 +1.5 3/3 methods agree	Labeled (related wording) related wording	serious PRR 3.4	no trial data cached
Inability to afford medication	19	27.1 17.3–42.4ROR 27.5 · χ² 451 / p 2e-100	26.4 EB05 17.9 · IC025 +3.2 3/3 methods agree	Not in label — unassessed	serious n=6	no trial data cached
Insurance issue	18	17.0 10.7–26.9ROR 17.2 · χ² 255 / p 1e-57	16.4 EB05 10.6 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious PRR 13.1	no trial data cached
Withdrawal syndrome	17	5.6 3.5–9.1ROR 5.7 · χ² 60 / p 4e-15	4.9 EB05 3.3 · IC025 +1.5 3/3 methods agree	Labeled (related wording) related wording	serious PRR 1.8	no trial data cached
Drug effect incomplete	16	6.1 3.7–9.9ROR 6.1 · χ² 63 / p 1e-15	5.3 EB05 3.4 · IC025 +1.6 3/3 methods agree	Reporting / coding artifact	serious PRR 2.9	no trial data cached
Sleep apnoea syndrome	16	11.7 7.2–19.1ROR 11.8 · χ² 146 / p 5e-34	10.5 EB05 6.4 · IC025 +2.3 3/3 methods agree	Not in label — unassessed	serious PRR 13.4	no trial data cached
Hospice care	16	22.8 14.0–37.1ROR 23.0 · χ² 311 / p 5e-70	22.2 EB05 14.3 · IC025 +2.9 3/3 methods agree	Not in label — unassessed	serious PRR 29.8	no trial data cached
Incorrect route of drug administration	13	5.0 2.9–8.6ROR 5.1 · χ² 38 / p 4e-10	4.3 EB05 2.7 · IC025 +1.2 3/3 methods agree	Reporting / coding artifact	serious PRR 5.6	no trial data cached
Intestinal perforation	13	16.2 9.4–27.9ROR 16.4 · χ² 171 / p 3e-39	15.2 EB05 8.7 · IC025 +2.4 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 15.7	no trial data cached
Needle issue	10	4.9 2.6–9.1ROR 4.9 · χ² 27 / p 9e-8	4.1 EB05 2.4 · IC025 +1.0 3/3 methods agree	Not in label — unassessed	serious n=6	no trial data cached
Muscle spasticity	10	11.3 6.1–21.0ROR 11.4 · χ² 84 / p 3e-20	9.2 EB05 4.8 · IC025 +1.8 3/3 methods agree	Not in label — unassessed	serious PRR 10.9	no trial data cached
Device issue	9	1.4 0.8–2.8ROR 1.4 · χ² 1 / p 0.181	1.4 EB05 0.8 · IC025 -0.6 PRR-only: not supported by EBGM or IC	Reporting / coding artifact	serious PRR 3.7	no trial data cached
Device malfunction	9	1.9 1.0–3.6ROR 1.9 · χ² 3 / p 0.045	1.8 EB05 1.0 · IC025 -0.3 PRR-only: not supported by EBGM or IC	Reporting / coding artifact	serious PRR 1.0	no trial data cached

Unlabeled candidate signals

Every screened signal with n ≥ 20 was either labeled, an indication term, or an artifact pattern — no unlabeled candidate stood out in the top signals.

Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.

Common questions

What are the most reported side effects of Methylnaltrexone?

In FDA FAERS, the most frequently co-reported reaction terms for Methylnaltrexone are drug withdrawal syndrome, inability to afford medication, insurance issue, withdrawal syndrome, sleep apnoea syndrome, hospice care. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.

Does Methylnaltrexone have an FDA boxed warning?

No. The FDA label retrieved for Methylnaltrexone has no boxed warning; see the label's Warnings and Precautions for the recognised risks.

Do FAERS signals prove that Methylnaltrexone causes these side effects?

No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.

Sources & methods

FDA label via openFDA (set ID c488fb7c-0a5b-487c-b452-996809d1cb99, effective 20240501; matched on openfda.generic_name.exact:"METHYLNALTREXONE BROMIDE")
Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA count= aggregation, field patient.drug.openfda.generic_name.exact, 39 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction
Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
Seriousness and sex counts from openFDA count=serious, patient.patientsex, seriousnessdeath

Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.