Drug · FAERS side-effect profile with label screen
Metaxalone side effects: what 3,321 FDA adverse event reports show
Who reports
3,321 reports · 62% serious · 603 with death outcome · 74% female
openFDA FAERS counts, all years, deduplication not applied
Used for
Metaxalone tablets are indicated as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions in adults and pediatric patients 13 years of age and older. Metaxalone t.
FDA label, Indications and Usage
What it is
Metaxalone Tablets, USP contain 800 mg of metaxalone and the following inactive ingredients: alginic acid, corn starch, ferric oxide red, copovidone, magnesium stearate, povidone, pregelatinized starch, sodium alginate. Metaxalone tablet is a muscle relaxant for oral administration.
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 40 strongest signals
Labeled adverse reaction 2Reporting / coding artifact 3Lab value / disease marker 1Outcome field, not a reaction 1Not in label — unassessed 33
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.
- 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.
- 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. 167 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 |
|---|---|---|---|---|---|---|
| Completed suicide (death by suicide) | 261 | 19.6 17.4–22.0ROR 21.2 · χ² 4,593 / p <1e-300 | 19.5 EB05 17.6 · IC025 +4.0 3/3 methods agree | Outcome field, not a reaction | serious PRR 18.1 · 97% clinician | no trial data cached |
| Serotonin syndrome | 59 | 19.5 15.1–25.1ROR 19.8 · χ² 1,014 / p 7e-223 | 19.3 EB05 15.5 · IC025 +3.6 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 18.2 · 96% clinician | no trial data cached |
| End stage renal disease | 36 | 12.3 8.9–17.1ROR 12.5 · χ² 363 / p 3e-81 | 11.9 EB05 8.8 · IC025 +2.9 3/3 methods agree | Not in label — unassessed | serious PRR 11.4 | no trial data cached |
| Muscle rigidity | 22 | 11.6 7.7–17.6ROR 11.7 · χ² 203 / p 3e-46 | 10.8 EB05 7.1 · IC025 +2.5 3/3 methods agree | Not in label — unassessed | serious PRR 12.1 · 91% clinician | no trial data cached |
| Poisoning | 23 | 11.5 7.7–17.3ROR 11.6 · χ² 210 / p 7e-48 | 10.7 EB05 7.2 · IC025 +2.5 3/3 methods agree | Not in label — unassessed | serious PRR 10.8 · 100% clinician | no trial data cached |
| Chronic kidney disease | 111 | 9.1 7.6–11.0ROR 9.4 · χ² 798 / p 8e-176 | 8.9 EB05 7.6 · IC025 +2.8 3/3 methods agree | Not in label — unassessed | serious PRR 8.6 | no trial data cached |
| Sleep apnoea syndrome | 27 | 8.9 6.1–13.0ROR 9.0 · χ² 182 / p 1e-41 | 8.1 EB05 5.7 · IC025 +2.3 3/3 methods agree | Not in label — unassessed | serious PRR 8.7 | no trial data cached |
| Fibromyalgia | 32 | 8.3 5.9–11.7ROR 8.4 · χ² 199 / p 2e-45 | 7.7 EB05 5.6 · IC025 +2.3 3/3 methods agree | Not in label — unassessed | serious PRR 7.6 | no trial data cached |
| Respiratory arrest | 35 | 7.9 5.7–11.0ROR 8.0 · χ² 205 / p 7e-47 | 7.4 EB05 5.5 · IC025 +2.3 3/3 methods agree | Not in label — unassessed | serious PRR 7.4 · 100% clinician | no trial data cached |
| Respiratory depression | 15 | 7.7 4.7–12.8ROR 7.7 · χ² 81 / p 1e-19 | 6.5 EB05 4.1 · IC025 +1.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 7.4 | no trial data cached |
| Nerve compression | 11 | 7.5 4.2–13.6ROR 7.6 · χ² 56 / p 4e-14 | 6.0 EB05 3.5 · IC025 +1.5 3/3 methods agree | Not in label — unassessed | serious PRR 7.7 | no trial data cached |
| Impaired gastric emptying | 15 | 7.4 4.5–12.3ROR 7.4 · χ² 77 / p 9e-19 | 6.3 EB05 4.0 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 7.7 | no trial data cached |
| Mydriasis | 15 | 7.4 4.5–12.2ROR 7.4 · χ² 76 / p 1e-18 | 6.2 EB05 3.9 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 8.8 | no trial data cached |
| Drug toxicity | 16 | 7.3 4.5–11.9ROR 7.3 · χ² 81 / p 1e-19 | 6.2 EB05 4.0 · IC025 +1.8 3/3 methods agree | Not in label — unassessed | serious PRR 7.0 | no trial data cached |
| Spinal operation | 14 | 7.3 4.3–12.3ROR 7.3 · χ² 70 / p 3e-17 | 6.1 EB05 3.8 · IC025 +1.7 3/3 methods agree | Reporting / coding artifact | serious PRR 7.4 | no trial data cached |
| Osteopenia | 17 | 7.0 4.4–11.3ROR 7.1 · χ² 82 / p 7e-20 | 6.0 EB05 4.0 · IC025 +1.8 3/3 methods agree | Not in label — unassessed | serious PRR 6.8 | no trial data cached |
| Cardio-respiratory arrest | 46 | 6.9 5.2–9.2ROR 7.0 · χ² 226 / p 2e-51 | 6.5 EB05 5.0 · IC025 +2.2 3/3 methods agree | Not in label — unassessed | serious PRR 6.4 · 100% clinician | no trial data cached |
| Vasculitis | 12 | 6.5 3.7–11.4ROR 6.5 · χ² 50 / p 6e-13 | 5.3 EB05 3.2 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 6.5 | no trial data cached |
| Bursitis | 12 | 6.3 3.6–11.0ROR 6.3 · χ² 48 / p 2e-12 | 5.2 EB05 3.1 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 6.8 | no trial data cached |
| Toxicity to various agents | 164 | 6.2 5.3–7.2ROR 6.4 · χ² 709 / p 2e-156 | 6.1 EB05 5.3 · IC025 +2.3 3/3 methods agree | Not in label — unassessed | serious PRR 5.9 · 95% clinician | no trial data cached |
| Blood sodium decreased | 18 | 6.0 3.8–9.6ROR 6.1 · χ² 71 / p 2e-17 | 5.3 EB05 3.5 · IC025 +1.6 3/3 methods agree | Lab value / disease marker | serious PRR 5.3 | no trial data cached |
| Back injury | 10 | 5.8 3.1–10.8ROR 5.8 · χ² 35 / p 1e-9 | 4.7 EB05 2.7 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 5.0 | no trial data cached |
| Disability | 18 | 5.7 3.6–9.1ROR 5.8 · χ² 66 / p 3e-16 | 5.1 EB05 3.4 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 4.9 | no trial data cached |
| Brain oedema | 11 | 5.5 3.0–9.9ROR 5.5 · χ² 36 / p 1e-9 | 4.5 EB05 2.7 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 5.1 | no trial data cached |
| Intervertebral disc protrusion | 19 | 5.5 3.5–8.6ROR 5.5 · χ² 65 / p 4e-16 | 4.9 EB05 3.3 · IC025 +1.5 3/3 methods agree | Not in label — unassessed | serious PRR 5.0 | no trial data cached |
| Foot fracture | 16 | 5.3 3.3–8.7ROR 5.3 · χ² 52 / p 3e-13 | 4.6 EB05 3.0 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 5.5 | no trial data cached |
| No therapeutic response | 10 | 5.1 2.7–9.5ROR 5.1 · χ² 29 / p 4e-8 | 4.2 EB05 2.5 · IC025 +1.0 3/3 methods agree | Reporting / coding artifact | serious PRR 5.3 | no trial data cached |
| Muscle tightness | 13 | 5.1 2.9–8.7ROR 5.1 · χ² 38 / p 3e-10 | 4.4 EB05 2.7 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 4.9 | no trial data cached |
| Osteoporosis | 33 | 5.1 3.6–7.1ROR 5.1 · χ² 103 / p 1e-24 | 4.7 EB05 3.5 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 5.2 | no trial data cached |
| Renal failure (kidney failure) | 107 | 5.0 4.2–6.1ROR 5.2 · χ² 345 / p 3e-77 | 4.9 EB05 4.2 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 4.7 | no trial data cached |
| Carpal tunnel syndrome | 11 | 4.9 2.7–8.9ROR 5.0 · χ² 31 / p 1e-8 | 4.2 EB05 2.5 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious PRR 4.6 | no trial data cached |
| Osteoarthritis | 33 | 4.9 3.5–6.9ROR 4.9 · χ² 99 / p 2e-23 | 4.6 EB05 3.4 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 4.6 | no trial data cached |
| Rotator cuff syndrome | 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 PRR 4.7 | no trial data cached |
| Sciatica | 12 | 4.8 2.7–8.4ROR 4.8 · χ² 32 / p 7e-9 | 4.1 EB05 2.5 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious PRR 5.4 | no trial data cached |
| Irritable bowel syndrome | 16 | 4.7 2.9–7.7ROR 4.7 · χ² 43 / p 2e-11 | 4.2 EB05 2.8 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 4.2 | no trial data cached |
| Tubulointerstitial nephritis | 14 | 4.7 2.8–7.9ROR 4.7 · χ² 37 / p 5e-10 | 4.1 EB05 2.6 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 4.4 | no trial data cached |
| Therapeutic response unexpected | 33 | 4.6 3.3–6.5ROR 4.7 · χ² 90 / p 1e-21 | 4.4 EB05 3.3 · IC025 +1.6 3/3 methods agree | Reporting / coding artifact | serious PRR 9.7 | no trial data cached |
| Glaucoma | 14 | 4.6 2.7–7.7ROR 4.6 · χ² 36 / p 1e-9 | 4.0 EB05 2.6 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious PRR 4.6 | no trial data cached |
| Ankle fracture | 11 | 4.5 2.5–8.1ROR 4.5 · χ² 26 / p 1e-7 | 3.8 EB05 2.3 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 3.8 | no trial data cached |
| Tendonitis | 11 | 4.5 2.5–8.0ROR 4.5 · χ² 26 / p 2e-7 | 3.8 EB05 2.3 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 5.3 | 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 |
|---|---|---|---|---|---|---|
| Completed suicide (death by suicide) | 261 | 19.6 17.4–22.0ROR 21.2 · χ² 4,593 / p <1e-300 | 19.5 EB05 17.6 · IC025 +4.0 3/3 methods agree | Outcome field, not a reaction | serious PRR 18.1 · 97% clinician | no trial data cached |
| Toxicity to various agents | 164 | 6.2 5.3–7.2ROR 6.4 · χ² 709 / p 2e-156 | 6.1 EB05 5.3 · IC025 +2.3 3/3 methods agree | Not in label — unassessed | serious PRR 5.9 · 95% clinician | no trial data cached |
| Fall | 159 | 3.0 2.6–3.5ROR 3.1 · χ² 215 / p 5e-49 | 3.0 EB05 2.6 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 2.6 | no trial data cached |
| Chronic kidney disease | 111 | 9.1 7.6–11.0ROR 9.4 · χ² 798 / p 8e-176 | 8.9 EB05 7.6 · IC025 +2.8 3/3 methods agree | Not in label — unassessed | serious PRR 8.6 | no trial data cached |
| Renal failure (kidney failure) | 107 | 5.0 4.2–6.1ROR 5.2 · χ² 345 / p 3e-77 | 4.9 EB05 4.2 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 4.7 | no trial data cached |
| Drug hypersensitivity | 97 | 3.1 2.6–3.8ROR 3.2 · χ² 141 / p 7e-33 | 3.1 EB05 2.6 · IC025 +1.3 3/3 methods agree | Labeled (related wording) related wording | serious PRR 1.7 | no trial data cached |
| Muscle spasms | 97 | 3.3 2.7–4.1ROR 3.4 · χ² 157 / p 2e-36 | 3.3 EB05 2.8 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 3.6 | no trial data cached |
| Acute kidney injury (sudden kidney damage) | 85 | 3.5 2.9–4.3ROR 3.6 · χ² 152 / p 4e-35 | 3.5 EB05 2.9 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 3.3 | no trial data cached |
| Sinusitis | 67 | 4.1 3.2–5.2ROR 4.2 · χ² 155 / p 6e-36 | 4.0 EB05 3.3 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 4.1 | no trial data cached |
| Overdose | 65 | 1.9 1.5–2.4ROR 1.9 · χ² 27 / p 1e-7 | 1.9 EB05 1.5 · IC025 +0.5 | Reporting / coding artifact | serious PRR 2.0 | no trial data cached |
| Memory impairment | 62 | 2.8 2.2–3.6ROR 2.9 · χ² 73 / p 8e-18 | 2.8 EB05 2.3 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious PRR 3.4 | no trial data cached |
| Migraine | 59 | 3.9 3.0–5.0ROR 4.0 · χ² 126 / p 2e-29 | 3.8 EB05 3.1 · IC025 +1.5 3/3 methods agree | Not in label — unassessed | serious PRR 4.3 | no trial data cached |
| Serotonin syndrome | 59 | 19.5 15.1–25.1ROR 19.8 · χ² 1,014 / p 7e-223 | 19.3 EB05 15.5 · IC025 +3.6 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 18.2 · 96% clinician | no trial data cached |
| Drug abuse | 58 | 4.4 3.4–5.6ROR 4.4 · χ² 148 / p 2e-34 | 4.2 EB05 3.4 · IC025 +1.7 3/3 methods agree | Reporting / coding artifact | serious PRR 4.1 · 96% clinician | no trial data cached |
| Bronchitis | 52 | 4.4 3.4–5.8ROR 4.5 · χ² 134 / p 3e-31 | 4.2 EB05 3.4 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 4.8 | 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.
- End stage renal disease — n=36, PRR 12.3
- Muscle rigidity — n=22, PRR 11.6
- Poisoning — n=23, PRR 11.5
- Chronic kidney disease — n=111, PRR 9.1
- Sleep apnoea syndrome — n=27, PRR 8.9
- Fibromyalgia — n=32, PRR 8.3
- Respiratory arrest — n=35, PRR 7.9
- Cardio-respiratory arrest — n=46, PRR 6.9
- Toxicity to various agents — n=164, PRR 6.2
- Osteoporosis — n=33, PRR 5.1
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 Metaxalone?
In FDA FAERS, the most frequently co-reported reaction terms for Metaxalone are toxicity to various agents, fall, chronic kidney disease, renal failure, drug hypersensitivity, muscle spasms. 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 Metaxalone have an FDA boxed warning?
No. The FDA label retrieved for Metaxalone has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Metaxalone 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 02eb5938-cd59-4a81-853d-a4148d813a94, effective 20250120; matched on
openfda.generic_name.exact:"METAXALONE") - 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, 207 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.