Drug · FAERS side-effect profile with label screen
Metronidazole side effects: what 63,491 FDA adverse event reports show
Drug class
FDA label (Established Pharmacologic Class) · compare the class
Who reports
63,491 reports · 84% serious · 6,851 with death outcome · 62% female
openFDA FAERS counts, all years, deduplication not applied
Used for
Symptomatic Trichomoniasis. Metronidazole tablets, USP are indicated for the treatment of T. vaginalis infection in females and males when the presence of the trichomonad has been confirmed by appropriate laboratory procedures (wet smears and/or cultures). Asymptomatic Trichomoniasis. Metronidazole tablets, USP are indicated in the treatment of asymptomatic T.
FDA label, Indications and Usage
What it is
DESCRIPTION Metronidazole tablets, 250 mg or 500 mg is an oral formulation of the synthetic nitroimidazole antimicrobial, 2-methyl-5-nitro-1H-imidazole-1-ethanol, which has the following structural formula: Metronidazole USP is a white to pale yellow, crystalline powder.
FDA label, Description section
Boxed warning
Metronidazole has been shown to be carcinogenic in mice and rats (see PRECAUTIONS ). Unnecessary use of the drug should be avoided. Its use should be reserved for the conditions described in the INDICATIONS AND USAGE section below.
FDA 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 40 strongest signals
Labeled adverse reaction 1Labeled (related wording) 3Likely indication confounding 9Reporting / coding artifact 6Lab value / disease marker 3Not in label — unassessed 18
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.
- Likely indication confounding The term appears in the label's indications: reports probably describe the disease being treated (or its progression), not a drug effect. Classic confounding by indication.
- 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.
- Lab value / disease marker A laboratory result, investigation or disease-activity marker (antibody positive, CRP abnormal, swollen joint count) not described in the label. These usually mirror the monitored disease or testing protocol rather than a drug effect; not screened further.
- 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, for the 300 most-reported drugs, adjusted for age band), and flags pairs whose reports are unusually skewed by sex or come mostly from consumers. Each row also shows the PRR against the other drugs of the same FDA class, which removes most confounding by the condition being treated, and a calibrated p-value: on validation, known non-causes average an ROR of about 2, so significance is judged against that empirical null (✓ = p < 0.05 after calibration). 1,198 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
Show:
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Vaginal flatulence | 250 | 1,561.8 1,158.6–2,105.3ROR 1,568.0 · calibrated p 6e-19 ✓ | 264.3 EB05 237.9 · IC025 +7.2 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.6 (3.9–5.5) | Likely indication confounding shares a disease stem with the indications wording | serious n=250 · ♀ 100% (drug 62%) | no trial arm names this drug |
| Appendicolith | 284 | 1,013.8 800.7–1,283.6ROR 1,018.4 · calibrated p 5e-17 ✓ | 242.8 EB05 220.0 · IC025 +7.2 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.5 (3.8–5.3) | Not in label — unassessed | serious n=284 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Sleep disorder therapy | 127 | 723.8 529.6–989.2ROR 725.2 · calibrated p 4e-15 ✓ | 217.6 EB05 187.6 · IC025 +6.6 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.5 (3.5–5.8) | Reporting / coding artifact | serious n=127 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Antacid therapy | 79 | 641.6 438.6–938.4ROR 642.4 · calibrated p 3e-14 ✓ | 205.6 EB05 170.3 · IC025 +6.1 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.5 (3.3–6.1) | Reporting / coding artifact | serious n=79 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Analgesic therapy | 120 | 213.0 169.2–268.1ROR 213.4 · calibrated p 4e-10 ✓ | 126.5 EB05 108.6 · IC025 +6.1 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.5 (3.5–5.8) | Reporting / coding artifact | serious n=120 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Drug therapy | 108 | 168.7 133.7–212.8ROR 169.0 · calibrated p 3e-9 ✓ | 109.3 EB05 93.0 · IC025 +5.9 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.5 (3.5–5.9) | Reporting / coding artifact | serious n=108 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Anticoagulant therapy | 78 | 129.3 99.5–168.0ROR 129.4 · calibrated p 3e-8 ✓ | 90.8 EB05 75.1 · IC025 +5.5 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.5 (3.3–6.2) | Reporting / coding artifact | serious n=78 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Congenital hiatus hernia | 51 | 98.6 72.1–134.9ROR 98.7 · calibrated p 2e-7 ✓ | 73.9 EB05 58.4 · IC025 +5.0 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.5 (3.1–6.6) | Not in label — unassessed | serious n=51 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Female genital tract fistula | 321 | 75.7 67.0–85.4ROR 76.1 · calibrated p 9e-7 ✓ | 61.4 EB05 55.9 · IC025 +5.6 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 5.2 (4.4–6.1) | Likely indication confounding shares a disease stem with the indications wording | serious n=319 · ♀ 100% (drug 62%) | no trial arm names this drug |
| Toxic encephalopathy | 657 | 50.6 46.7–55.0ROR 51.2 · calibrated p 1e-5 ✓ | 43.9 EB05 41.1 · IC025 +5.3 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.7 (4.2–5.2) | Labeled (related wording) related wording | serious n=656 · ♀ 38% (drug 62%) · 100% clinician | no trial arm names this drug |
| Dysmetria | 71 | 44.0 34.4–56.4ROR 44.1 · calibrated p 4e-5 ✓ | 38.5 EB05 31.6 · IC025 +4.5 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 5.2 (3.7–7.2) | Not in label — unassessed | serious n=71 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Radiculopathy | 285 | 39.9 35.3–45.2ROR 40.1 · calibrated p 5e-5 ✓ | 35.6 EB05 32.3 · IC025 +4.9 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.9 (4.1–5.8) | Not in label — unassessed | serious n=285 · ♀ 100% (drug 62%) | no trial arm names this drug |
| Pseudomembranous colitis | 241 | 39.7 34.7–45.3ROR 39.8 · calibrated p 6e-5 ✓ | 35.4 EB05 31.8 · IC025 +4.8 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 5.9 (4.9–7.2) | Not in label — unassessed | serious n=241 · 92% clinician | no trial arm names this drug |
| Cerebellar ataxia | 103 | 39.5 32.2–48.5ROR 39.6 · calibrated p 7e-5 ✓ | 35.1 EB05 29.8 · IC025 +4.6 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 5.2 (3.9–6.8) | Labeled (related wording) related wording | serious n=101 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Proctitis | 299 | 39.3 34.9–44.3ROR 39.5 · calibrated p 6e-5 ✓ | 35.1 EB05 31.9 · IC025 +4.9 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.8 (4.1–5.7) | Labeled adverse reaction exact term | serious n=299 · ♀ 91% (drug 62%) | no trial arm names this drug |
| Pouchitis | 88 | 37.5 30.1–46.7ROR 37.5 · calibrated p 9e-5 ✓ | 33.5 EB05 28.0 · IC025 +4.5 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 7.5 (5.3–10.5) | Not in label — unassessed | serious n=84 | no trial arm names this drug |
| Bloody discharge | 114 | 36.2 29.9–44.0ROR 36.3 · calibrated p 1e-4 ✓ | 32.5 EB05 27.8 · IC025 +4.5 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 5.0 (3.8–6.5) | Not in label — unassessed | serious n=113 · ♀ 100% (drug 62%) · 100% clinician | no trial arm names this drug |
| Cerebellar syndrome | 218 | 36.0 31.3–41.4ROR 36.2 · calibrated p 1e-4 ✓ | 32.5 EB05 29.0 · IC025 +4.7 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 5.1 (4.2–6.2) | Labeled (related wording) related wording | serious n=217 · 100% clinician | no trial arm names this drug |
| Fistula discharge | 110 | 31.3 25.7–38.0ROR 31.3 · calibrated p 2e-4 ✓ | 28.5 EB05 24.3 · IC025 +4.4 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 8.1 (5.9–11.1) | Not in label — unassessed | serious n=105 | no trial arm names this drug |
| Chronic sinusitis | 313 | 30.0 26.8–33.7ROR 30.2 · calibrated p 3e-4 ✓ | 27.5 EB05 25.1 · IC025 +4.5 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.8 (4.1–5.7) | Not in label — unassessed | serious n=311 · ♀ 100% (drug 62%) | no trial arm names this drug |
| Hyperphosphataemia | 171 | 28.9 24.7–33.8ROR 29.0 · calibrated p 3e-4 ✓ | 26.6 EB05 23.4 · IC025 +4.4 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.7 (3.8–5.8) | Not in label — unassessed | serious n=170 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| International normalised ratio fluctuation | 163 | 27.8 23.7–32.6ROR 27.9 · calibrated p 4e-4 ✓ | 25.6 EB05 22.5 · IC025 +4.3 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 5.0 (4.0–6.3) | Lab value / disease marker | serious n=162 · ♀ 100% (drug 62%) · 90% clinician | no trial arm names this drug |
| Megacolon | 121 | 27.6 22.9–33.2ROR 27.7 · calibrated p 4e-4 ✓ | 25.4 EB05 21.8 · IC025 +4.2 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 5.0 (3.8–6.4) | Not in label — unassessed | serious n=121 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Clostridium difficile colitis | 819 | 27.5 25.7–29.6ROR 27.9 · calibrated p 4e-4 ✓ | 25.5 EB05 24.0 · IC025 +4.5 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 6.3 (5.7–7.0) | Likely indication confounding shares a disease stem with the indications wording | age-adj. PRR 23.8 · serious PRR 17.6 | no trial arm names this drug |
| Abortion incomplete | 140 | 26.4 22.2–31.4ROR 26.5 · calibrated p 6e-4 ✓ | 24.4 EB05 21.2 · IC025 +4.2 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 5.2 (4.1–6.6) | Not in label — unassessed | ♀ 100% (drug 62%) · 100% clinician | no trial arm names this drug |
| Macular degeneration | 862 | 25.7 24.0–27.5ROR 26.0 · calibrated p 6e-4 ✓ | 23.9 EB05 22.6 · IC025 +4.4 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.6 (4.1–5.0) | Not in label — unassessed | serious PRR 17.6 · ♀ 100% (drug 62%) | no trial arm names this drug |
| Blood phosphorus increased | 195 | 25.4 22.0–29.4ROR 25.5 · calibrated p 7e-4 ✓ | 23.6 EB05 20.9 · IC025 +4.2 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.7 (3.8–5.7) | Lab value / disease marker | serious n=195 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Pelvic abscess | 80 | 24.8 19.8–31.1ROR 24.8 · calibrated p 8e-4 ✓ | 23.0 EB05 19.1 · IC025 +4.0 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 10.3 (6.9–15.3) | Likely indication confounding shares a disease stem with the indications wording | serious n=80 | no trial arm names this drug |
| Clostridium colitis | 84 | 24.3 19.5–30.3ROR 24.3 · calibrated p 9e-4 ✓ | 22.6 EB05 18.8 · IC025 +4.0 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 6.9 (4.9–9.7) | Likely indication confounding shares a disease stem with the indications wording | serious n=84 · 100% clinician | no trial arm names this drug |
| Enterocutaneous fistula | 60 | 24.2 18.6–31.5ROR 24.2 · calibrated p 1e-3 ✓ | 22.5 EB05 18.1 · IC025 +3.8 3/3 methods agree vs other Nitroimidazole Antimicrobials: only this drug | Not in label — unassessed | serious n=60 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Bronchopulmonary aspergillosis allergic | 62 | 23.9 18.5–30.9ROR 23.9 · calibrated p 0.001 ✓ | 22.2 EB05 17.9 · IC025 +3.8 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.5 (3.2–6.4) | Not in label — unassessed | serious n=62 · ♀ 0% (drug 62%) · 100% clinician | no trial arm names this drug |
| Clostridium test positive | 140 | 22.6 19.0–26.8ROR 22.6 · calibrated p 0.001 ✓ | 21.1 EB05 18.4 · IC025 +4.0 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 6.6 (5.1–8.5) | Lab value / disease marker | serious n=134 | no trial arm names this drug |
| Dysbiosis | 51 | 22.4 16.9–29.7ROR 22.4 · calibrated p 0.001 ✓ | 20.9 EB05 16.5 · IC025 +3.7 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.8 (3.2–7.1) | Not in label — unassessed | serious n=51 · ♀ 100% (drug 62%) · 100% clinician | no trial arm names this drug |
| Chronic kidney disease-mineral and bone disorder | 68 | 22.2 17.4–28.4ROR 22.2 · calibrated p 0.001 ✓ | 20.8 EB05 16.9 · IC025 +3.8 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 5.1 (3.6–7.2) | Not in label — unassessed | serious n=68 | no trial arm names this drug |
| Perirectal abscess | 68 | 21.4 16.7–27.3ROR 21.4 · calibrated p 0.002 ✓ | 20.0 EB05 16.3 · IC025 +3.7 3/3 methods agree vs other Nitroimidazole Antimicrobials: only this drug | Likely indication confounding shares a disease stem with the indications wording | serious n=68 · ♀ 0% (drug 62%) | no trial arm names this drug |
| Anal fistula | 316 | 20.7 18.5–23.2ROR 20.8 · calibrated p 0.002 ✓ | 19.5 EB05 17.8 · IC025 +4.1 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 10.8 (8.8–13.2) | Not in label — unassessed | serious n=310 | no trial arm names this drug |
| Rectal abscess | 99 | 20.6 16.8–25.2ROR 20.6 · calibrated p 0.002 ✓ | 19.4 EB05 16.4 · IC025 +3.8 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 10.6 (7.4–15.2) | Likely indication confounding shares a disease stem with the indications wording | serious n=96 | no trial arm names this drug |
| Bacterial vaginosis | 89 | 20.1 16.2–24.8ROR 20.1 · calibrated p 0.002 ✓ | 18.9 EB05 15.8 · IC025 +3.8 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 8.0 (5.7–11.3) | Likely indication confounding shares a disease stem with the indications wording | serious n=56 · ♀ 100% (drug 62%) | no trial arm names this drug |
| Pathogen resistance | 492 | 18.8 17.2–20.6ROR 19.0 · calibrated p 0.003 ✓ | 17.8 EB05 16.6 · IC025 +4.0 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 4.6 (4.0–5.2) | Reporting / coding artifact | serious PRR 12.7 · ♀ 28% (drug 62%) · 100% clinician | no trial arm names this drug |
| Clostridium difficile infection | 1,167 | 18.7 17.7–19.9ROR 19.1 · calibrated p 0.002 ✓ | 17.8 EB05 16.9 · IC025 +4.0 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 6.0 (5.5–6.5) | Likely indication confounding shares a disease stem with the indications wording | age-adj. PRR 16.4 · serious PRR 12.5 | no trial arm names this drug |
Clinical concept groups
MedDRA splits one clinical problem across several terms (e.g. "neutropenia", "neutrophil count decreased", "agranulocytosis"), which dilutes term-level signals. These rows count reports with any term in a concept group (an exact union, not a sum), compared with all other drugs. Groups are hand-built and listed in the methods.
| Concept | Reports | PRR 95% CI | Reading |
|---|---|---|---|
| Severe cutaneous reaction | 1,710 | 7.77.4–8.1 | signal |
| Anaphylaxis / angioedema | 1,324 | 3.53.3–3.7 | signal |
| Hyponatraemia | 759 | 3.12.9–3.4 | signal |
| Pancreatitis | 741 | 3.12.8–3.3 | signal |
| Tendon disorder | 347 | 3.02.7–3.4 | signal |
| Kidney injury | 3,949 | 2.92.8–3.0 | signal |
| Liver injury | 2,492 | 2.72.6–2.9 | signal |
| Gi bleeding | 1,451 | 2.62.5–2.8 | signal |
| Anaemia | 2,344 | 2.62.5–2.7 | signal |
| Neutropenia / agranulocytosis | 1,751 | 2.32.2–2.5 | signal |
| Serious infection | 5,066 | 2.22.1–2.2 | signal |
| Thrombocytopenia | 1,395 | 2.12.0–2.2 | raised |
| Venous thromboembolism | 1,331 | 2.01.9–2.1 | raised |
| Arrhythmia / qt | 1,108 | 1.91.8–2.0 | raised |
| Opportunistic infection | 723 | 1.81.6–1.9 | raised |
| Depression | 1,298 | 1.51.4–1.6 | raised |
Trial evidence (ClinicalTrials.gov)
ClinicalTrials.gov returned results-bearing trials mentioning Metronidazole only as a background or rescue medication (NCT02800785, NCT01241552); no trial listing it as the tested intervention was cached, so no trial cross-check is shown.
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 |
|---|---|---|---|---|---|---|
| Drug ineffective (drug did not work) | 5,467 | 1.4 1.3–1.4ROR 1.4 · calibrated p 0.580 | 1.4 EB05 1.3 · IC025 +0.4 vs other Nitroimidazole Antimicrobials: PRR 5.4 (5.2–5.6) | Reporting / coding artifact | age-adj. PRR 1.5 · serious PRR 2.3 | no trial arm names this drug |
| Nausea | 4,686 | 2.0 1.9–2.0ROR 2.0 · calibrated p 0.968 | 2.0 EB05 1.9 · IC025 +0.9 vs other Nitroimidazole Antimicrobials: PRR 6.2 (5.9–6.4) | Labeled adverse reaction exact term | age-adj. PRR 1.8 · serious PRR 2.2 | no trial arm names this drug |
| Off label use (used outside approved label) | 4,152 | 1.6 1.5–1.6ROR 1.6 · calibrated p 0.721 | 1.6 EB05 1.5 · IC025 +0.6 vs other Nitroimidazole Antimicrobials: PRR 5.6 (5.4–5.9) | Reporting / coding artifact | age-adj. PRR 1.5 · serious PRR 1.8 | no trial arm names this drug |
| Diarrhoea (diarrhea) | 4,094 | 2.1 2.0–2.2ROR 2.2 · calibrated p 0.959 | 2.1 EB05 2.0 · IC025 +1.0 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 6.9 (6.6–7.2) | Labeled adverse reaction exact term | age-adj. PRR 1.9 · serious PRR 2.2 | no trial arm names this drug |
| Vomiting | 3,316 | 2.3 2.3–2.4ROR 2.4 · calibrated p 0.848 | 2.3 EB05 2.3 · IC025 +1.2 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 6.5 (6.2–6.8) | Labeled adverse reaction exact term | age-adj. PRR 2.1 · serious PRR 2.1 | no trial arm names this drug |
| Pyrexia (fever) | 3,246 | 3.1 3.0–3.2ROR 3.2 · calibrated p 0.556 | 3.1 EB05 3.0 · IC025 +1.6 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 6.5 (6.1–6.8) | Labeled (related wording) related wording | age-adj. PRR 2.6 · serious PRR 2.5 | no trial arm names this drug |
| Drug hypersensitivity | 3,150 | 5.4 5.2–5.6ROR 5.7 · calibrated p 0.174 | 5.4 EB05 5.2 · IC025 +2.4 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 10.9 (10.3–11.6) | Labeled (related wording) related wording | age-adj. PRR 5.0 · serious PRR 3.3 · ♀ 83% (drug 62%) | no trial arm names this drug |
| Pain | 3,047 | 1.6 1.6–1.7ROR 1.7 · calibrated p 0.751 | 1.6 EB05 1.6 · IC025 +0.6 vs other Nitroimidazole Antimicrobials: PRR 6.5 (6.2–6.9) | Labeled adverse reaction exact term | age-adj. PRR 1.7 · serious PRR 1.6 | no trial arm names this drug |
| Abdominal pain | 3,011 | 4.3 4.2–4.5ROR 4.5 · calibrated p 0.298 | 4.3 EB05 4.1 · IC025 +2.0 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 6.5 (6.1–6.9) | Labeled (related wording) related wording | age-adj. PRR 3.7 · serious PRR 3.7 | no trial arm names this drug |
| Headache | 2,868 | 1.5 1.5–1.6ROR 1.5 · calibrated p 0.667 | 1.5 EB05 1.5 · IC025 +0.5 vs other Nitroimidazole Antimicrobials: PRR 5.8 (5.5–6.2) | Labeled — boxed warning exact term | age-adj. PRR 1.4 · serious PRR 1.9 | no trial arm names this drug |
| Fatigue (tiredness) | 2,839 | 1.2 1.2–1.3ROR 1.2 · calibrated p 0.452 | 1.2 EB05 1.2 · IC025 +0.2 vs other Nitroimidazole Antimicrobials: PRR 6.6 (6.3–7.0) | Not in label — unassessed | age-adj. PRR 1.1 · serious PRR 1.4 | no trial arm names this drug |
| Dyspnoea (shortness of breath) | 2,225 | 1.3 1.2–1.4ROR 1.3 · calibrated p 0.515 | 1.3 EB05 1.3 · IC025 +0.3 vs other Nitroimidazole Antimicrobials: PRR 6.4 (6.0–6.8) | Not in label — unassessed | age-adj. PRR 1.2 · serious PRR 1.2 | no trial arm names this drug |
| Dizziness | 2,177 | 1.4 1.4–1.5ROR 1.5 · calibrated p 0.616 | 1.4 EB05 1.4 · IC025 +0.5 vs other Nitroimidazole Antimicrobials: PRR 5.9 (5.5–6.3) | Labeled — boxed warning exact term | age-adj. PRR 1.3 · serious PRR 1.5 | no trial arm names this drug |
| Condition aggravated | 2,137 | 2.3 2.3–2.4ROR 2.4 · calibrated p 0.860 | 2.3 EB05 2.3 · IC025 +1.2 3/3 methods agree vs other Nitroimidazole Antimicrobials: PRR 6.0 (5.7–6.4) | Reporting / coding artifact | age-adj. PRR 2.0 · serious PRR 2.3 | no trial arm names this drug |
| Malaise (feeling unwell) | 2,000 | 1.5 1.4–1.6ROR 1.5 · calibrated p 0.656 | 1.5 EB05 1.4 · IC025 +0.5 vs other Nitroimidazole Antimicrobials: PRR 6.2 (5.8–6.6) | Not in label — unassessed | age-adj. PRR 1.4 · serious PRR 1.6 | no trial arm names this drug |
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.
- Appendicolith — n=284, PRR 1,013.8
- Congenital hiatus hernia — n=51, PRR 98.6
- Dysmetria — n=71, PRR 44.0
- Radiculopathy — n=285, PRR 39.9
- Pseudomembranous colitis — n=241, PRR 39.7
- Pouchitis — n=88, PRR 37.5
- Bloody discharge — n=114, PRR 36.2
- Fistula discharge — n=110, PRR 31.3
- Chronic sinusitis — n=313, PRR 30.0
- Hyperphosphataemia — n=171, PRR 28.9
✓ A hand-written Bradford Hill causality assessment exists for this drug: Metronidazole ↔ Peripheral neuropathy.
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 Metronidazole?
In FDA FAERS, the most frequently co-reported reaction terms for Metronidazole are nausea, diarrhoea, vomiting, pyrexia, drug hypersensitivity, pain. 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 Metronidazole have an FDA boxed warning?
Yes. The current FDA label carries a boxed warning: Metronidazole has been shown to be carcinogenic in mice and rats (see PRECAUTIONS ). Unnecessary use of the drug should be avoided. Its use should be reserved for the conditions described in the INDICATIONS AND USAGE section below.
Do FAERS signals prove that Metronidazole 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 06bd4afb-4a45-294c-e063-6394a90a7ab1, effective 20260101; matched on
openfda.generic_name.exact:"METRONIDAZOLE") - 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, fieldpatient.drug.openfda.generic_name.exact, 1,238 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 - ClinicalTrials.gov API v2 (query
METRONIDAZOLE, results-bearing studies sorted by enrollment)
Page generated 2026-10-14. 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.