Mebendazole side effects: what 783 FDA adverse event reports show

Mebendazole · Vermox · 17 reaction terms · 230 drug–reaction co-reports · data 2026-09-14

Drug class

Anthelmintic

FDA label (Established Pharmacologic Class) · compare the class

Brand names

Vermox

openFDA label

Who reports

783 reports · 90% serious · 56 with death outcome · 60% female

openFDA FAERS counts, all years, deduplication not applied

Used for

VERMOX™ CHEWABLE is indicated for the treatment of patients one year of age and older with gastrointestinal infections caused by Ascaris lumbricoides (roundworm) and Trichuris trichiura (whipworm). VERMOX™ CHEWABLE is an anthelmintic indicated for the treatment of patients one year of age and older with gastrointestinal infections caused by: Ascaris lumbricoides (roundworm) and Trichuris trichiura (whipworm) ( 1 ).

FDA label, Indications and Usage

What it is

VERMOX™ CHEWABLE (mebendazole chewable tablets) is an orally administered anthelmintic.

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 13 strongest signals

Labeled adverse reaction 1Reporting / coding artifact 6Not in label — unassessed 6

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.
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.
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. 4 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
Laryngitis	10	24.7 13.3–45.7ROR 25.0 · χ² 204 / p 2e-46	23.4 EB05 13.2 · IC025 +2.5 3/3 methods agree	Not in label — unassessed	serious n=10	no trial data cached
Intentional self-injury	18	23.9 15.1–37.7ROR 24.4 · χ² 372 / p 3e-83	23.3 EB05 15.5 · IC025 +3.1 3/3 methods agree	Reporting / coding artifact	serious PRR 15.4	no trial data cached
Drug exposure during pregnancy	30	23.3 16.4–33.1ROR 24.2 · χ² 618 / p 1e-136	23.0 EB05 16.8 · IC025 +3.5 3/3 methods agree	Reporting / coding artifact	serious PRR 15.4 · ♀ 89% (drug 60%)	no trial data cached
Foetal exposure during pregnancy	57	18.8 14.6–24.1ROR 20.2 · χ² 945 / p 1e-207	18.7 EB05 14.9 · IC025 +3.6 3/3 methods agree	Reporting / coding artifact	serious PRR 12.3 · ♀ 30% (drug 60%) · 100% clinician	no trial data cached
Poisoning	7	14.8 7.1–31.0ROR 15.0 · χ² 77 / p 8e-19	11.9 EB05 4.9 · IC025 +1.6 3/3 methods agree	Not in label — unassessed	serious PRR 9.6	no trial data cached
Abortion spontaneous	21	14.0 9.2–21.3ROR 14.3 · χ² 240 / p 2e-54	13.4 EB05 8.8 · IC025 +2.7 3/3 methods agree	Not in label — unassessed	serious PRR 9.0 · ♀ 100% (drug 60%)	no trial data cached
Paranoia	7	10.8 5.2–22.6ROR 10.9 · χ² 53 / p 2e-13	7.9 EB05 3.6 · IC025 +1.4 3/3 methods agree	Not in label — unassessed	serious PRR 8.7	no trial data cached
Exposure during pregnancy	22	9.5 6.3–14.3ROR 9.7 · χ² 159 / p 1e-36	8.5 EB05 5.7 · IC025 +2.3 3/3 methods agree	Reporting / coding artifact	serious PRR 8.7 · ♀ 100% (drug 60%)	no trial data cached
Hepatocellular injury	5	9.4 3.9–22.5ROR 9.5 · χ² 30 / p 3e-8	6.0 EB05 2.6 · IC025 +0.9 3/3 methods agree	Not in label — unassessed	serious PRR 6.0	no trial data cached
Agranulocytosis (severe loss of white cells)	6	8.7 3.9–19.3ROR 8.7 · χ² 33 / p 4e-9	5.9 EB05 2.8 · IC025 +1.0 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 5.5	no trial data cached
Dystonia	6	8.2 3.7–18.3ROR 8.3 · χ² 31 / p 1e-8	5.6 EB05 2.7 · IC025 +1.0 3/3 methods agree	Not in label — unassessed	serious PRR 5.8	no trial data cached
Intentional overdose	12	5.0 2.9–8.8ROR 5.1 · χ² 35 / p 2e-9	4.3 EB05 2.6 · IC025 +1.1 3/3 methods agree	Reporting / coding artifact	serious PRR 3.3	no trial data cached
Drug abuse	14	4.5 2.7–7.5ROR 4.5 · χ² 35 / p 2e-9	4.0 EB05 2.5 · IC025 +1.1 3/3 methods agree	Reporting / coding artifact	serious PRR 2.9	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
Foetal exposure during pregnancy	57	18.8 14.6–24.1ROR 20.2 · χ² 945 / p 1e-207	18.7 EB05 14.9 · IC025 +3.6 3/3 methods agree	Reporting / coding artifact	serious PRR 12.3 · ♀ 30% (drug 60%) · 100% clinician	no trial data cached
Drug exposure during pregnancy	30	23.3 16.4–33.1ROR 24.2 · χ² 618 / p 1e-136	23.0 EB05 16.8 · IC025 +3.5 3/3 methods agree	Reporting / coding artifact	serious PRR 15.4 · ♀ 89% (drug 60%)	no trial data cached
Exposure during pregnancy	22	9.5 6.3–14.3ROR 9.7 · χ² 159 / p 1e-36	8.5 EB05 5.7 · IC025 +2.3 3/3 methods agree	Reporting / coding artifact	serious PRR 8.7 · ♀ 100% (drug 60%)	no trial data cached
Abortion spontaneous	21	14.0 9.2–21.3ROR 14.3 · χ² 240 / p 2e-54	13.4 EB05 8.8 · IC025 +2.7 3/3 methods agree	Not in label — unassessed	serious PRR 9.0 · ♀ 100% (drug 60%)	no trial data cached
Intentional self-injury	18	23.9 15.1–37.7ROR 24.4 · χ² 372 / p 3e-83	23.3 EB05 15.5 · IC025 +3.1 3/3 methods agree	Reporting / coding artifact	serious PRR 15.4	no trial data cached
Drug abuse	14	4.5 2.7–7.5ROR 4.5 · χ² 35 / p 2e-9	4.0 EB05 2.5 · IC025 +1.1 3/3 methods agree	Reporting / coding artifact	serious PRR 2.9	no trial data cached
Intentional overdose	12	5.0 2.9–8.8ROR 5.1 · χ² 35 / p 2e-9	4.3 EB05 2.6 · IC025 +1.1 3/3 methods agree	Reporting / coding artifact	serious PRR 3.3	no trial data cached
Laryngitis	10	24.7 13.3–45.7ROR 25.0 · χ² 204 / p 2e-46	23.4 EB05 13.2 · IC025 +2.5 3/3 methods agree	Not in label — unassessed	serious n=10	no trial data cached
Paranoia	7	10.8 5.2–22.6ROR 10.9 · χ² 53 / p 2e-13	7.9 EB05 3.6 · IC025 +1.4 3/3 methods agree	Not in label — unassessed	serious PRR 8.7	no trial data cached
Poisoning	7	14.8 7.1–31.0ROR 15.0 · χ² 77 / p 8e-19	11.9 EB05 4.9 · IC025 +1.6 3/3 methods agree	Not in label — unassessed	serious PRR 9.6	no trial data cached
Dystonia	6	8.2 3.7–18.3ROR 8.3 · χ² 31 / p 1e-8	5.6 EB05 2.7 · IC025 +1.0 3/3 methods agree	Not in label — unassessed	serious PRR 5.8	no trial data cached
Agranulocytosis (severe loss of white cells)	6	8.7 3.9–19.3ROR 8.7 · χ² 33 / p 4e-9	5.9 EB05 2.8 · IC025 +1.0 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 5.5	no trial data cached
Hepatocellular injury	5	9.4 3.9–22.5ROR 9.5 · χ² 30 / p 3e-8	6.0 EB05 2.6 · IC025 +0.9 3/3 methods agree	Not in label — unassessed	serious PRR 6.0	no trial data cached
Tardive dyskinesia (persistent involuntary movements)	4	3.8 1.4–10.0ROR 3.8 · χ² 6 / p 0.009	2.9 EB05 1.3 · IC025 -0.2 PRR-only: not supported by EBGM or IC	Not in label — unassessed	serious PRR 2.9	no trial data cached
Pregnancy	4	5.3 2.0–14.1ROR 5.3 · χ² 10 / p 8e-4	3.6 EB05 1.6 · IC025 +0.1	Not in label — unassessed	serious PRR 3.7	no trial data cached

Unlabeled candidate signals

These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.

Abortion spontaneous — n=21, PRR 14.0

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 Mebendazole?

In FDA FAERS, the most frequently co-reported reaction terms for Mebendazole are abortion spontaneous, laryngitis, paranoia, poisoning, dystonia, agranulocytosis. 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 Mebendazole have an FDA boxed warning?

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

Do FAERS signals prove that Mebendazole 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 a720c424-517a-461b-8e13-6c37caf8aa3f, effective 20211005; matched on openfda.generic_name.exact:"MEBENDAZOLE")
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, 17 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.