Drug · FAERS side-effect profile with label screen
Cyclobenzaprine Hydrochloride side effects: what 8,909 FDA adverse event reports show
Drug class
Not stated in label
Brand names
Cyclobenzaprine Hydrochloride
openFDA label
Who reports
8,909 reports · 58% serious · 731 with death outcome · 77% female
openFDA FAERS counts, all years, deduplication not applied
Used for
Cyclobenzaprine hydrochloride tablets,USP are indicated as an adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions. Improvement is manifested by relief of muscle spasm and its associated signs and symptoms, namely, pain, tenderness, limitation of motion, and restriction in activities of daily living.
FDA label, Indications and Usage
What it is
DESCRIPTION Cyclobenzaprine hydrochloride, USP is a white, crystalline tricyclic amine salt with the empirical formula C 20 H 21 N•HCl and a molecular weight of 311.9. It has a melting point of 217°C, and a pK a of 8.47 at 25°C.
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 (related wording) 2Reporting / coding artifact 4Lab value / disease marker 6Outcome field, not a reaction 1Not in label — unassessed 27
What the badges mean
- 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.
- 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. 1,042 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 |
|---|---|---|---|---|---|---|
| Temperature regulation disorder | 328 | 415.2 369.8–466.1ROR 431.0 · χ² 114,578 / p <1e-300 | 345.1 EB05 314.9 · IC025 +7.7 3/3 methods agree | Not in label — unassessed | serious n=328 · ♀ 100% (drug 77%) | no trial arm names this drug |
| Sedation complication | 242 | 251.7 220.8–286.9ROR 258.7 · χ² 54,282 / p <1e-300 | 223.1 EB05 200.5 · IC025 +7.1 3/3 methods agree | Reporting / coding artifact | serious n=242 · ♀ 100% (drug 77%) | no trial arm names this drug |
| Creatinine renal clearance decreased | 241 | 149.3 131.3–169.8ROR 153.5 · χ² 33,227 / p <1e-300 | 138.8 EB05 124.7 · IC025 +6.6 3/3 methods agree | Lab value / disease marker | serious n=240 · ♀ 99% (drug 77%) | no trial arm names this drug |
| Multiple drug therapy | 37 | 131.4 94.4–182.9ROR 131.9 · χ² 4,408 / p <1e-300 | 117.0 EB05 88.7 · IC025 +5.0 3/3 methods agree | Reporting / coding artifact | serious n=37 · ♀ 100% (drug 77%) · 100% clinician | no trial arm names this drug |
| Food allergy | 387 | 126.7 114.7–140.1ROR 132.4 · χ² 45,671 / p <1e-300 | 119.5 EB05 109.9 · IC025 +6.5 3/3 methods agree | Not in label — unassessed | serious n=383 · ♀ 100% (drug 77%) | no trial arm names this drug |
| Creatinine renal clearance increased | 28 | 90.8 62.3–132.4ROR 91.1 · χ² 2,307 / p <1e-300 | 82.6 EB05 60.0 · IC025 +4.5 3/3 methods agree | Lab value / disease marker | serious n=28 · ♀ 100% (drug 77%) · 100% clinician | no trial arm names this drug |
| Coeliac disease | 336 | 83.2 74.8–92.6ROR 86.4 · χ² 26,267 / p <1e-300 | 80.0 EB05 73.1 · IC025 +6.0 3/3 methods agree | Not in label — unassessed | serious PRR 97.1 · ♀ 100% (drug 77%) | no trial arm names this drug |
| Foetal death | 176 | 82.5 71.1–95.7ROR 84.1 · χ² 13,602 / p <1e-300 | 79.0 EB05 69.7 · IC025 +5.8 3/3 methods agree | Not in label — unassessed | serious n=176 · ♀ 100% (drug 77%) · 92% clinician | no trial arm names this drug |
| Bursitis | 368 | 73.8 66.7–81.7ROR 77.0 · χ² 25,565 / p <1e-300 | 71.3 EB05 65.4 · IC025 +5.9 3/3 methods agree | Not in label — unassessed | serious PRR 83.3 · ♀ 99% (drug 77%) | no trial arm names this drug |
| Immunodeficiency | 400 | 65.5 59.4–72.2ROR 68.5 · χ² 24,664 / p <1e-300 | 63.5 EB05 58.5 · IC025 +5.7 3/3 methods agree | Not in label — unassessed | serious PRR 68.6 · ♀ 99% (drug 77%) | no trial arm names this drug |
| Blood calcium decreased | 247 | 52.5 46.4–59.5ROR 54.0 · χ² 12,163 / p <1e-300 | 51.2 EB05 46.0 · IC025 +5.3 3/3 methods agree | Lab value / disease marker | serious PRR 63.7 · ♀ 99% (drug 77%) | no trial arm names this drug |
| Blepharospasm | 122 | 47.1 39.4–56.2ROR 47.7 · χ² 5,346 / p <1e-300 | 45.8 EB05 39.4 · IC025 +5.0 3/3 methods agree | Not in label — unassessed | serious n=120 · ♀ 100% (drug 77%) | no trial arm names this drug |
| Groin infection | 10 | 44.3 23.7–82.7ROR 44.3 · χ² 374 / p 2e-83 | 40.4 EB05 23.4 · IC025 +2.8 3/3 methods agree | Not in label — unassessed | serious n=9 | no trial arm names this drug |
| Infusion site discharge | 31 | 43.3 30.4–61.8ROR 43.5 · χ² 1,217 / p 7e-267 | 41.5 EB05 30.7 · IC025 +4.1 3/3 methods agree | Not in label — unassessed | serious n=23 · 100% consumer | no trial arm names this drug |
| Orthostatic hypotension (dizziness on standing) | 251 | 34.2 30.3–38.7ROR 35.2 · χ² 7,956 / p <1e-300 | 33.7 EB05 30.3 · IC025 +4.8 3/3 methods agree | Not in label — unassessed | serious PRR 37.8 · ♀ 99% (drug 77%) | no trial arm names this drug |
| Infusion site mass | 15 | 33.4 20.1–55.6ROR 33.5 · χ² 434 / p 1e-96 | 31.8 EB05 20.4 · IC025 +3.1 3/3 methods agree | Not in label — unassessed | serious n=13 | no trial arm names this drug |
| Periorbital pain | 11 | 32.6 18.0–59.1ROR 32.6 · χ² 302 / p 6e-68 | 30.6 EB05 18.2 · IC025 +2.7 3/3 methods agree | Not in label — unassessed | – | no trial arm names this drug |
| Prescribed overdose | 262 | 32.2 28.6–36.3ROR 33.1 · χ² 7,789 / p <1e-300 | 31.7 EB05 28.6 · IC025 +4.7 3/3 methods agree | Not in label — unassessed | serious PRR 53.3 | no trial arm names this drug |
| Sciatic nerve injury | 10 | 28.3 15.2–52.8ROR 28.4 · χ² 234 / p 4e-53 | 26.6 EB05 15.2 · IC025 +2.5 3/3 methods agree | Not in label — unassessed | serious n=8 | no trial arm names this drug |
| Renal function test abnormal | 49 | 25.3 19.1–33.5ROR 25.4 · χ² 1,108 / p 3e-243 | 24.8 EB05 19.5 · IC025 +3.9 3/3 methods agree | Reporting / coding artifact | serious n=47 · ♀ 100% (drug 77%) | no trial arm names this drug |
| Sedation | 269 | 24.5 21.7–27.5ROR 25.2 · χ² 5,974 / p <1e-300 | 24.2 EB05 21.9 · IC025 +4.3 3/3 methods agree | Not in label — unassessed | serious PRR 31.7 · ♀ 97% (drug 77%) | no trial arm names this drug |
| Upper respiratory tract infection (cold/sinus infection) | 473 | 24.3 22.2–26.5ROR 25.6 · χ² 10,456 / p <1e-300 | 24.0 EB05 22.3 · IC025 +4.4 3/3 methods agree | Labeled (related wording) related wording | serious PRR 37.9 | no trial arm names this drug |
| Facet joint syndrome | 32 | 24.1 17.0–34.1ROR 24.1 · χ² 677 / p 1e-149 | 23.5 EB05 17.4 · IC025 +3.6 3/3 methods agree | Not in label — unassessed | serious n=32 · 100% clinician | no trial arm names this drug |
| Contraindicated product administered | 286 | 22.5 20.0–25.2ROR 23.2 · χ² 5,795 / p <1e-300 | 22.2 EB05 20.1 · IC025 +4.2 3/3 methods agree | Reporting / coding artifact | serious PRR 27.1 · ♀ 100% (drug 77%) | no trial arm names this drug |
| Lupus vulgaris | 11 | 21.9 12.1–39.6ROR 21.9 · χ² 197 / p 5e-45 | 20.7 EB05 11.8 · IC025 +2.5 3/3 methods agree | Not in label — unassessed | serious n=11 | no trial arm names this drug |
| Infusion site haemorrhage | 29 | 21.2 14.7–30.5ROR 21.2 · χ² 533 / p 3e-118 | 20.7 EB05 15.1 · IC025 +3.4 3/3 methods agree | Not in label — unassessed | serious n=21 · 76% consumer | no trial arm names this drug |
| Infusion site reaction | 26 | 21.2 14.4–31.1ROR 21.2 · χ² 475 / p 1e-105 | 20.7 EB05 14.8 · IC025 +3.3 3/3 methods agree | Not in label — unassessed | serious n=24 · ♀ 100% (drug 77%) | no trial arm names this drug |
| Deep vein thrombosis postoperative | 17 | 20.5 12.7–33.0ROR 20.5 · χ² 294 / p 4e-66 | 19.8 EB05 12.9 · IC025 +2.9 3/3 methods agree | Not in label — unassessed | serious n=17 | no trial arm names this drug |
| Red blood cell sedimentation rate abnormal | 20 | 20.3 13.1–31.6ROR 20.4 · χ² 346 / p 2e-77 | 19.8 EB05 13.4 · IC025 +3.0 3/3 methods agree | Lab value / disease marker | serious n=20 | no trial arm names this drug |
| Rheumatic fever | 37 | 20.0 14.5–27.7ROR 20.1 · χ² 645 / p 1e-142 | 19.7 EB05 14.9 · IC025 +3.4 3/3 methods agree | Not in label — unassessed | serious n=37 · ♀ 100% (drug 77%) · 100% clinician | no trial arm names this drug |
| Infusion site bruising | 18 | 20.0 12.6–31.8ROR 20.1 · χ² 304 / p 2e-68 | 19.4 EB05 12.8 · IC025 +2.9 3/3 methods agree | Not in label — unassessed | serious n=12 | no trial arm names this drug |
| X-ray abnormal | 15 | 19.9 12.0–33.0ROR 19.9 · χ² 248 / p 3e-56 | 19.1 EB05 11.9 · IC025 +2.7 3/3 methods agree | Lab value / disease marker | serious n=15 | no trial arm names this drug |
| Cardiac death | 10 | 19.3 10.4–36.0ROR 19.4 · χ² 155 / p 8e-36 | 17.9 EB05 9.4 · IC025 +2.3 3/3 methods agree | Outcome field, not a reaction | serious n=10 | no trial arm names this drug |
| Infusion site pruritus | 25 | 19.0 12.8–28.1ROR 19.0 · χ² 404 / p 3e-90 | 18.5 EB05 13.1 · IC025 +3.1 3/3 methods agree | Labeled (related wording) related wording | serious n=17 · 80% consumer | no trial arm names this drug |
| Rash erythematous | 374 | 18.9 17.1–20.9ROR 19.7 · χ² 6,278 / p <1e-300 | 18.7 EB05 17.2 · IC025 +4.0 3/3 methods agree | Not in label — unassessed | serious PRR 36.4 · ♀ 98% (drug 77%) | no trial arm names this drug |
| Derealisation | 17 | 18.8 11.7–30.3ROR 18.8 · χ² 267 / p 3e-60 | 18.1 EB05 11.7 · IC025 +2.8 3/3 methods agree | Not in label — unassessed | serious n=17 | no trial arm names this drug |
| Fluid retention | 402 | 18.7 17.0–20.6ROR 19.5 · χ² 6,679 / p <1e-300 | 18.5 EB05 17.1 · IC025 +4.0 3/3 methods agree | Not in label — unassessed | serious PRR 24.9 | no trial arm names this drug |
| Eyelid pain | 15 | 18.3 11.0–30.4ROR 18.3 · χ² 226 / p 2e-51 | 17.5 EB05 10.8 · IC025 +2.7 3/3 methods agree | Not in label — unassessed | – | no trial arm names this drug |
| Onychomadesis | 32 | 18.2 12.9–25.8ROR 18.3 · χ² 499 / p 6e-111 | 17.9 EB05 13.2 · IC025 +3.2 3/3 methods agree | Not in label — unassessed | serious n=32 · ♀ 100% (drug 77%) · 100% clinician | no trial arm names this drug |
| Blood pressure diastolic abnormal | 19 | 17.5 11.1–27.4ROR 17.5 · χ² 277 / p 2e-62 | 16.9 EB05 11.1 · IC025 +2.8 3/3 methods agree | Lab value / disease marker | serious n=19 | no trial arm names this drug |
Trial evidence (ClinicalTrials.gov)
ClinicalTrials.gov returned results-bearing trials mentioning Cyclobenzaprine only as a background or rescue medication (NCT02436096, NCT04508621); 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 |
|---|---|---|---|---|---|---|
| Pain | 1,391 | 5.3 5.1–5.6ROR 6.1 · χ² 5,006 / p <1e-300 | 5.3 EB05 5.1 · IC025 +2.3 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 7.0 | no trial arm names this drug |
| Headache | 1,075 | 4.0 3.8–4.3ROR 4.5 · χ² 2,522 / p <1e-300 | 4.0 EB05 3.8 · IC025 +1.9 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 6.2 | no trial arm names this drug |
| Fatigue (tiredness) | 1,060 | 3.2 3.0–3.4ROR 3.5 · χ² 1,666 / p <1e-300 | 3.2 EB05 3.0 · IC025 +1.6 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.4 | no trial arm names this drug |
| Drug ineffective (drug did not work) | 811 | 1.4 1.4–1.5ROR 1.5 · χ² 118 / p 7e-28 | 1.4 EB05 1.4 · IC025 +0.4 | Reporting / coding artifact | serious PRR 2.5 | no trial arm names this drug |
| Off label use (used outside approved label) | 740 | 2.0 1.9–2.1ROR 2.1 · χ² 386 / p 3e-86 | 2.0 EB05 1.9 · IC025 +0.9 | Reporting / coding artifact | serious PRR 3.0 | no trial arm names this drug |
| Nausea | 732 | 2.2 2.0–2.3ROR 2.3 · χ² 483 / p 2e-107 | 2.2 EB05 2.0 · IC025 +1.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.8 | no trial arm names this drug |
| Constipation | 710 | 7.7 7.2–8.3ROR 8.3 · χ² 4,178 / p <1e-300 | 7.7 EB05 7.2 · IC025 +2.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 12.8 | no trial arm names this drug |
| Back pain | 646 | 6.5 6.1–7.0ROR 7.0 · χ² 3,050 / p <1e-300 | 6.5 EB05 6.1 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious PRR 9.2 | no trial arm names this drug |
| Fall | 626 | 4.4 4.1–4.8ROR 4.7 · χ² 1,680 / p <1e-300 | 4.4 EB05 4.1 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 4.8 | no trial arm names this drug |
| Dyspnoea (shortness of breath) | 548 | 2.3 2.1–2.5ROR 2.4 · χ² 401 / p 2e-89 | 2.3 EB05 2.1 · IC025 +1.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.5 | no trial arm names this drug |
| Rheumatoid arthritis | 537 | 11.2 10.3–12.2ROR 11.8 · χ² 4,979 / p <1e-300 | 11.1 EB05 10.3 · IC025 +3.3 3/3 methods agree | Not in label — unassessed | serious PRR 13.3 | no trial arm names this drug |
| Diarrhoea (diarrhea) | 517 | 1.9 1.7–2.1ROR 1.9 · χ² 221 / p 2e-50 | 1.9 EB05 1.8 · IC025 +0.8 | Labeled adverse reaction exact term | serious PRR 2.2 | no trial arm names this drug |
| Product dose omission issue | 513 | 4.2 3.9–4.6ROR 4.4 · χ² 1,279 / p 2e-280 | 4.2 EB05 3.9 · IC025 +1.9 3/3 methods agree | Reporting / coding artifact | serious PRR 8.6 | no trial arm names this drug |
| Rash | 503 | 2.7 2.5–3.0ROR 2.8 · χ² 558 / p 1e-123 | 2.7 EB05 2.5 · IC025 +1.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.4 | no trial arm names this drug |
| Drug hypersensitivity | 503 | 6.1 5.6–6.6ROR 6.4 · χ² 2,150 / p <1e-300 | 6.0 EB05 5.6 · IC025 +2.4 3/3 methods agree | Labeled (related wording) related wording | serious PRR 14.5 | 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.
- Temperature regulation disorder — n=328, PRR 415.2
- Food allergy — n=387, PRR 126.7
- Coeliac disease — n=336, PRR 83.2
- Foetal death — n=176, PRR 82.5
- Bursitis — n=368, PRR 73.8
- Immunodeficiency — n=400, PRR 65.5
- Blepharospasm — n=122, PRR 47.1
- Infusion site discharge — n=31, PRR 43.3
- Orthostatic hypotension — n=251, PRR 34.2
- Prescribed overdose — n=262, PRR 32.2
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 Cyclobenzaprine?
In FDA FAERS, the most frequently co-reported reaction terms for Cyclobenzaprine are pain, headache, fatigue, nausea, constipation, back 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 Cyclobenzaprine have an FDA boxed warning?
No. The FDA label retrieved for Cyclobenzaprine has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Cyclobenzaprine 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 3bc7e2b4-e1a0-66e3-e063-6294a90a676a, effective 20250807; matched on
openfda.generic_name.exact:"CYCLOBENZAPRINE") - 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, 1,082 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
CYCLOBENZAPRINE, results-bearing studies sorted by enrollment)
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.