Cephalexin side effects: what 21,504 FDA adverse event reports show
Drug class
Cephalosporin antibacterial drug
Who reports
21,504 reports · 74% serious · 1,795 with death outcome · 64% female
Used for
Cephalexin USP is a cephalosporin antibacterial drug indicated for the treatment of the following infections caused by susceptible isolates of designated bacteria: Respiratory tract infection ( 1.1 ) Otitis media ( 1.2 ) Skin and skin structure infecti.
What it is
Cephalexin for oral suspension, USP is a semisynthetic cephalosporin antibacterial drug intended for oral administration. It is 7- (D-α-Amino-α-phenylacetamido)-3-methyl-3-cephem-4-carboxylic acid monohydrate. Cephalexin has the molecular formula C 16 H 17 N 3 O 4 S • H 2 O and the molecular weight is 365.41.
Boxed warning
None in the current label
Causality screen of the 40 strongest signals
What the badges mean
- 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). 1,177 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Pulmonary vasculitis | 170 | 464.0 386.6–557.0ROR 467.7 · calibrated p 2e-13 ✓ | 302.6 EB05 266.3 · IC025 +7.1 3/3 methods agree | Not in label — unassessed | serious n=170 · ♀ 0% (drug 64%) | not reported in cached trials |
| Total lung capacity abnormal | 119 | 444.9 358.1–552.6ROR 447.3 · calibrated p 3e-13 ✓ | 290.2 EB05 249.0 · IC025 +6.8 3/3 methods agree | Not in label — unassessed | serious n=119 · ♀ 0% (drug 64%) | not reported in cached trials |
| Capillaritis | 63 | 299.6 225.9–397.5ROR 300.5 · calibrated p 2e-11 ✓ | 213.9 EB05 173.1 · IC025 +5.9 3/3 methods agree | Not in label — unassessed | serious n=63 · ♀ 0% (drug 64%) | not reported in cached trials |
| Spirometry abnormal | 114 | 235.0 191.6–288.3ROR 236.3 · calibrated p 1e-10 ✓ | 183.3 EB05 156.7 · IC025 +6.4 3/3 methods agree | Lab value / disease marker | serious n=114 · ♀ 0% (drug 64%) | not reported in cached trials |
| Mite allergy | 121 | 228.4 187.4–278.3ROR 229.7 · calibrated p 2e-10 ✓ | 179.5 EB05 154.2 · IC025 +6.4 3/3 methods agree | Not in label — unassessed | serious n=121 · ♀ 0% (drug 64%) | not reported in cached trials |
| Mycotic allergy | 122 | 165.1 136.3–200.0ROR 166.0 · calibrated p 3e-9 ✓ | 138.0 EB05 118.7 · IC025 +6.2 3/3 methods agree | Not in label — unassessed | serious n=122 · ♀ 0% (drug 64%) | not reported in cached trials |
| Antineutrophil cytoplasmic antibody positive | 103 | 160.6 130.5–197.8ROR 161.4 · calibrated p 4e-9 ✓ | 134.4 EB05 114.0 · IC025 +6.0 3/3 methods agree | Lab value / disease marker | serious n=103 · ♀ 0% (drug 64%) | not reported in cached trials |
| Dust allergy | 120 | 138.6 114.5–167.7ROR 139.3 · calibrated p 1e-8 ✓ | 119.0 EB05 102.2 · IC025 +6.0 3/3 methods agree | Not in label — unassessed | serious n=120 · ♀ 0% (drug 64%) | not reported in cached trials |
| Chronic kidney disease-mineral and bone disorder | 125 | 128.2 106.4–154.4ROR 128.9 · calibrated p 2e-8 ✓ | 111.3 EB05 95.9 · IC025 +6.0 3/3 methods agree | Not in label — unassessed | serious n=125 | not reported in cached trials |
| Neuritis | 177 | 126.7 108.4–148.1ROR 127.8 · calibrated p 2e-8 ✓ | 110.8 EB05 97.7 · IC025 +6.2 3/3 methods agree | Not in label — unassessed | serious n=175 · ♀ 0% (drug 64%) | not reported in cached trials |
| Hyperparathyroidism secondary | 267 | 114.9 101.3–130.4ROR 116.4 · calibrated p 4e-8 ✓ | 102.0 EB05 92.2 · IC025 +6.2 3/3 methods agree | Not in label — unassessed | serious n=267 | not reported in cached trials |
| Nephrogenic anaemia | 458 | 105.9 96.2–116.5ROR 108.2 · calibrated p 7e-8 ✓ | 95.1 EB05 88.0 · IC025 +6.3 3/3 methods agree | Not in label — unassessed | serious n=458 | not reported in cached trials |
| Congenital multiplex arthrogryposis | 18 | 93.0 57.3–150.8ROR 93.1 · calibrated p 8e-7 ✓ | 78.1 EB05 52.3 · IC025 +3.9 3/3 methods agree | Not in label — unassessed | serious n=18 | not reported in cached trials |
| Conjunctivitis allergic | 119 | 86.3 71.6–104.0ROR 86.8 · calibrated p 4e-7 ✓ | 78.3 EB05 67.2 · IC025 +5.6 3/3 methods agree | Not in label — unassessed | serious n=119 · ♀ 0% (drug 64%) | not reported in cached trials |
| Eosinophilic granulomatosis with polyangiitis | 156 | 81.6 69.3–96.0ROR 82.2 · calibrated p 6e-7 ✓ | 74.6 EB05 65.3 · IC025 +5.7 3/3 methods agree | Not in label — unassessed | serious n=156 · ♀ 0% (drug 64%) | not reported in cached trials |
| Rebound acid hypersecretion | 234 | 80.5 70.5–91.9ROR 81.4 · calibrated p 6e-7 ✓ | 73.9 EB05 66.3 · IC025 +5.8 3/3 methods agree | Not in label — unassessed | serious n=234 | not reported in cached trials |
| Reversible airways obstruction | 34 | 68.9 48.7–97.6ROR 69.0 · calibrated p 3e-6 ✓ | 62.2 EB05 46.6 · IC025 +4.5 3/3 methods agree | Not in label — unassessed | serious n=34 · ♀ 0% (drug 64%) · 100% consumer | not reported in cached trials |
| Respiratory symptom | 170 | 62.9 53.9–73.5ROR 63.4 · calibrated p 3e-6 ✓ | 58.8 EB05 51.7 · IC025 +5.4 3/3 methods agree | Not in label — unassessed | serious n=169 · ♀ 0% (drug 64%) | not reported in cached trials |
| Alveolar osteitis | 22 | 53.0 34.5–81.4ROR 53.0 · calibrated p 2e-5 ✓ | 48.3 EB05 33.6 · IC025 +3.9 3/3 methods agree | Not in label — unassessed | serious n=22 | not reported in cached trials |
| Forced expiratory volume decreased | 127 | 45.6 38.2–54.5ROR 45.9 · calibrated p 3e-5 ✓ | 43.4 EB05 37.4 · IC025 +4.9 3/3 methods agree | Lab value / disease marker | serious n=127 · ♀ 0% (drug 64%) | not reported in cached trials |
| Clostridium test positive | 94 | 43.9 35.7–53.9ROR 44.1 · calibrated p 4e-5 ✓ | 41.7 EB05 35.1 · IC025 +4.8 3/3 methods agree | Lab value / disease marker | serious n=93 · 100% clinician | not reported in cached trials |
| Normochromic normocytic anaemia | 125 | 42.3 35.4–50.6ROR 42.6 · calibrated p 4e-5 ✓ | 40.3 EB05 34.7 · IC025 +4.8 3/3 methods agree | Not in label — unassessed | serious n=125 · ♀ 0% (drug 64%) | not reported in cached trials |
| Oesophageal spasm | 72 | 39.6 31.3–50.1ROR 39.7 · calibrated p 7e-5 ✓ | 37.7 EB05 31.0 · IC025 +4.5 3/3 methods agree | Not in label — unassessed | serious n=72 · ♀ 100% (drug 64%) | not reported in cached trials |
| End stage renal disease | 707 | 38.9 36.1–41.9ROR 40.2 · calibrated p 5e-5 ✓ | 37.4 EB05 35.1 · IC025 +5.1 3/3 methods agree | Not in label — unassessed | serious PRR 29.1 | not reported in cached trials |
| Neurological symptom | 191 | 33.9 29.4–39.2ROR 34.2 · calibrated p 1e-4 ✓ | 32.7 EB05 29.0 · IC025 +4.7 3/3 methods agree | Not in label — unassessed | serious n=191 · ♀ 10% (drug 64%) | not reported in cached trials |
| Loss of employment | 95 | 31.3 25.6–38.4ROR 31.5 · calibrated p 2e-4 ✓ | 30.2 EB05 25.4 · IC025 +4.4 3/3 methods agree | Not in label — unassessed | serious n=95 · ♀ 88% (drug 64%) | not reported in cached trials |
| Pulmonary alveolar haemorrhage | 174 | 31.2 26.9–36.3ROR 31.5 · calibrated p 2e-4 ✓ | 30.2 EB05 26.6 · IC025 +4.6 3/3 methods agree | Not in label — unassessed | serious n=174 · ♀ 0% (drug 64%) | not reported in cached trials |
| Bone demineralisation | 30 | 28.3 19.7–40.7ROR 28.4 · calibrated p 5e-4 ✓ | 27.1 EB05 19.9 · IC025 +3.7 3/3 methods agree | Not in label — unassessed | serious n=26 · ♀ 0% (drug 64%) | not reported in cached trials |
| Chronic kidney disease | 2,157 | 28.2 27.1–29.4ROR 31.2 · calibrated p 2e-4 ✓ | 27.4 EB05 26.5 · IC025 +4.7 3/3 methods agree | Not in label — unassessed | serious PRR 21.7 | not reported in cached trials |
| Vertebral foraminal stenosis | 20 | 24.1 15.5–37.6ROR 24.2 · calibrated p 0.001 ✓ | 23.1 EB05 15.7 · IC025 +3.2 3/3 methods agree | Not in label — unassessed | serious n=20 | not reported in cached trials |
| Arteriosclerosis coronary artery | 155 | 23.4 20.0–27.4ROR 23.6 · calibrated p 1e-3 ✓ | 22.8 EB05 19.9 · IC025 +4.2 3/3 methods agree | Not in label — unassessed | serious n=156 · ♀ 9% (drug 64%) | not reported in cached trials |
| Ureteric obstruction | 29 | 21.1 14.6–30.4ROR 21.1 · calibrated p 0.002 ✓ | 20.4 EB05 14.8 · IC025 +3.3 3/3 methods agree | Not in label — unassessed | serious n=29 · ♀ 100% (drug 64%) | not reported in cached trials |
| Obstructive sleep apnoea syndrome | 29 | 20.7 14.3–29.8ROR 20.7 · calibrated p 0.002 ✓ | 20.0 EB05 14.5 · IC025 +3.3 3/3 methods agree | Not in label — unassessed | serious n=29 · ♀ 100% (drug 64%) | not reported in cached trials |
| Arteriosclerosis | 187 | 19.7 17.1–22.8ROR 19.9 · calibrated p 0.002 ✓ | 19.3 EB05 17.1 · IC025 +4.0 3/3 methods agree | Not in label — unassessed | serious PRR 15.5 · ♀ 23% (drug 64%) | not reported in cached trials |
| Cerumen impaction | 18 | 19.4 12.2–30.9ROR 19.4 · calibrated p 0.004 ✓ | 18.5 EB05 12.2 · IC025 +2.9 3/3 methods agree | Not in label — unassessed | serious n=18 | not reported in cached trials |
| Oesophageal pain | 76 | 19.1 15.2–24.0ROR 19.2 · calibrated p 0.003 ✓ | 18.7 EB05 15.4 · IC025 +3.7 3/3 methods agree | Not in label — unassessed | serious n=74 · ♀ 100% (drug 64%) | not reported in cached trials |
| Seborrhoeic keratosis | 28 | 19.0 13.0–27.6ROR 19.0 · calibrated p 0.003 ✓ | 18.4 EB05 13.2 · IC025 +3.2 3/3 methods agree | Not in label — unassessed | serious n=27 | not reported in cached trials |
| Osteosclerosis | 30 | 18.9 13.2–27.1ROR 18.9 · calibrated p 0.003 ✓ | 18.3 EB05 13.3 · IC025 +3.2 3/3 methods agree | Not in label — unassessed | serious n=30 | not reported in cached trials |
| Obstructive airways disorder | 211 | 18.8 16.4–21.5ROR 18.9 · calibrated p 0.003 ✓ | 18.4 EB05 16.4 · IC025 +3.9 3/3 methods agree | Not in label — unassessed | serious PRR 15.0 · ♀ 17% (drug 64%) | not reported in cached trials |
| Cerebral palsy | 18 | 18.7 11.7–29.7ROR 18.7 · calibrated p 0.004 ✓ | 17.8 EB05 11.6 · IC025 +2.8 3/3 methods agree | Not in label — unassessed | serious n=18 | not reported in cached trials |
Trial evidence (ClinicalTrials.gov)
✓ Trial adverse-event data found on ClinicalTrials.gov
Largest completed trials with posted results that list Cephalexin as a study intervention. The right-hand column of the signal table shows whether each FAERS term was also recorded in these trials, with a real denominator (0 of 40 signal terms matched).
- NCT00729937 — Strategies Using Off-Patent Antibiotics for Methicillin Resistant S. Aureus "STOP MRSA" (N=2265, PHASE2, PHASE3; 62 AE terms posted; arms: Abscess, Placebo; Abscess, TMP/SMX; Infected Wound, TMP/SMX; Infected Wound, Clindamycin)
Caveats: trial populations, doses and follow-up differ from the reporting population; AE terms are sponsor-coded and matched here by wording; absence from a trial list means the term was not reported above the sponsor's frequency threshold, not that it cannot occur.
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 |
|---|---|---|---|---|---|---|
| Chronic kidney disease | 2,157 | 28.2 27.1–29.4ROR 31.2 · calibrated p 2e-4 ✓ | 27.4 EB05 26.5 · IC025 +4.7 3/3 methods agree | Not in label — unassessed | serious PRR 21.7 | not reported in cached trials |
| Renal failure (kidney failure) | 1,558 | 11.5 10.9–12.0ROR 12.3 · calibrated p 0.015 ✓ | 11.3 EB05 10.9 · IC025 +3.4 3/3 methods agree | Labeled (related wording) related wording | serious PRR 8.9 | NCT00729937: 1/248 (0.4%) on Cephalexin (serious AE) |
| Acute kidney injury (sudden kidney damage) | 1,550 | 10.0 9.5–10.5ROR 10.7 · calibrated p 0.025 ✓ | 9.9 EB05 9.5 · IC025 +3.2 3/3 methods agree | Labeled (related wording) related wording | serious PRR 7.7 | not reported in cached trials |
| Diarrhoea (diarrhea) | 1,405 | 2.1 2.0–2.2ROR 2.2 · calibrated p 0.946 | 2.1 EB05 2.0 · IC025 +1.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.2 | NCT00729937: 47/248 (19.0%) on Cephalexin; 96/617 (15.6%) control |
| Pain | 1,397 | 2.2 2.1–2.3ROR 2.3 · calibrated p 0.903 | 2.2 EB05 2.1 · IC025 +1.1 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.3 | NCT00729937: 1/630 (0.2%) on Cephalexin (serious AE) |
| Fatigue (tiredness) | 1,302 | 1.6 1.6–1.7ROR 1.7 · calibrated p 0.754 | 1.6 EB05 1.6 · IC025 +0.6 | Labeled adverse reaction exact term | serious PRR 1.7 | not reported in cached trials |
| Nausea | 1,297 | 1.6 1.5–1.7ROR 1.6 · calibrated p 0.733 | 1.6 EB05 1.5 · IC025 +0.6 | Labeled adverse reaction exact term | serious PRR 1.8 | NCT00729937: 41/248 (16.5%) on Cephalexin; 102/617 (16.5%) control |
| Dyspnoea (shortness of breath) | 1,215 | 2.1 2.0–2.2ROR 2.2 · calibrated p 0.971 | 2.1 EB05 2.0 · IC025 +1.0 | Not in label — unassessed | serious PRR 2.0 | not reported in cached trials |
| Anxiety | 1,154 | 4.0 3.7–4.2ROR 4.1 · calibrated p 0.356 | 3.9 EB05 3.7 · IC025 +1.9 3/3 methods agree | Not in label — unassessed | serious PRR 4.2 | not reported in cached trials |
| Headache | 1,153 | 1.8 1.7–1.9ROR 1.8 · calibrated p 0.854 | 1.8 EB05 1.7 · IC025 +0.7 | Labeled adverse reaction exact term | serious PRR 2.3 | NCT00729937: 42/248 (16.9%) on Cephalexin; 76/617 (12.3%) control |
| Rash | 1,141 | 2.6 2.4–2.7ROR 2.7 · calibrated p 0.749 | 2.6 EB05 2.4 · IC025 +1.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.9 | NCT00729937: 5/248 (2.0%) on Cephalexin; 9/617 (1.5%) control |
| Drug ineffective (drug did not work) | 1,047 | 0.8 0.7–0.8ROR 0.8 · calibrated p 0.164 | 0.8 EB05 0.7 · IC025 -0.5 PRR-only: not supported by EBGM or IC | Reporting / coding artifact | serious PRR 1.2 | not reported in cached trials |
| Off label use (used outside approved label) | 932 | 1.0 1.0–1.1ROR 1.0 · calibrated p 0.339 | 1.0 EB05 1.0 · IC025 -0.0 PRR-only: not supported by EBGM or IC | Reporting / coding artifact | serious PRR 1.2 | not reported in cached trials |
| Dizziness | 874 | 1.7 1.6–1.8ROR 1.7 · calibrated p 0.795 | 1.7 EB05 1.6 · IC025 +0.7 | Labeled adverse reaction exact term | serious PRR 1.9 | NCT00729937: 16/248 (6.5%) on Cephalexin; 39/617 (6.3%) control |
| Vomiting | 864 | 1.8 1.7–1.9ROR 1.8 · calibrated p 0.848 | 1.8 EB05 1.7 · IC025 +0.7 | Labeled adverse reaction exact term | serious PRR 1.7 | NCT00729937: 19/248 (7.7%) on Cephalexin; 40/617 (6.5%) control |
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.
- Pulmonary vasculitis — n=170, PRR 464.0
- Total lung capacity abnormal — n=119, PRR 444.9
- Capillaritis — n=63, PRR 299.6
- Mite allergy — n=121, PRR 228.4
- Mycotic allergy — n=122, PRR 165.1
- Dust allergy — n=120, PRR 138.6
- Chronic kidney disease-mineral and bone disorder — n=125, PRR 128.2
- Neuritis — n=177, PRR 126.7
- Hyperparathyroidism secondary — n=267, PRR 114.9
- Nephrogenic anaemia — n=458, PRR 105.9
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 Cephalexin?
In FDA FAERS, the most frequently co-reported reaction terms for Cephalexin are chronic kidney disease, renal failure, acute kidney injury, diarrhoea, pain, fatigue. 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 Cephalexin have an FDA boxed warning?
No. The FDA label retrieved for Cephalexin has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Cephalexin 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 0a24b6e5-6f13-44b4-93f4-47c86945cad2, effective 20230426; matched on
openfda.generic_name.exact:"CEPHALEXIN") - 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, 1,217 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
CEPHALEXIN, 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.