Drug · FAERS side-effect profile with label screen
Phenytoin Sodium side effects: what 3,989 FDA adverse event reports show
Who reports
3,989 reports · 83% serious · 327 with death outcome · 51% female
openFDA FAERS counts, all years, deduplication not applied
Used for
Phenytoin chewable tablets are indicated for the treatment of generalized tonic-clonic (grand mal) and complex partial (psychomotor, temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery. Phenytoin .
FDA label, Indications and Usage
What it is
Phenytoin is related to the barbiturates in chemical structure, but has a five-membered ring.
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 9Labeled (related wording) 5Likely indication confounding 3Reporting / coding artifact 5Lab value / disease marker 1Not in label — unassessed 17
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 flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 143 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 |
|---|---|---|---|---|---|---|
| Ataxia | 112 | 49.9 41.5–59.9ROR 51.3 · χ² 5,265 / p <1e-300 | 49.0 EB05 41.8 · IC025 +5.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 35.6 · 92% clinician | no trial data cached |
| Status epilepticus | 100 | 46.8 38.6–56.9ROR 48.0 · χ² 4,404 / p <1e-300 | 46.1 EB05 39.0 · IC025 +4.9 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 32.4 | no trial data cached |
| Drug level decreased | 70 | 36.2 28.7–45.7ROR 36.8 · χ² 2,346 / p <1e-300 | 35.6 EB05 29.2 · IC025 +4.5 3/3 methods agree | Reporting / coding artifact | serious PRR 25.2 | no trial data cached |
| Grand mal convulsion | 60 | 33.9 26.3–43.6ROR 34.4 · χ² 1,870 / p <1e-300 | 33.3 EB05 26.8 · IC025 +4.3 3/3 methods agree | Not in label — unassessed | serious PRR 22.2 | no trial data cached |
| Convulsion (seizure) | 289 | 26.3 23.5–29.4ROR 28.3 · χ² 6,996 / p <1e-300 | 26.1 EB05 23.7 · IC025 +4.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 18.1 | no trial data cached |
| Epilepsy | 124 | 21.4 18.0–25.5ROR 22.1 · χ² 2,389 / p <1e-300 | 21.3 EB05 18.3 · IC025 +4.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 14.8 | no trial data cached |
| Drug reaction with eosinophilia and systemic symptoms | 92 | 19.0 15.5–23.2ROR 19.4 · χ² 1,546 / p <1e-300 | 18.9 EB05 15.8 · IC025 +3.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 13.2 · 96% clinician | no trial data cached |
| Stevens-johnson syndrome (severe blistering skin reaction) | 79 | 18.7 15.0–23.3ROR 19.1 · χ² 1,302 / p 2e-285 | 18.6 EB05 15.4 · IC025 +3.7 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 13.1 | no trial data cached |
| Toxic epidermal necrolysis (severe skin peeling reaction) | 47 | 16.4 12.4–21.8ROR 16.6 · χ² 664 / p 1e-146 | 16.2 EB05 12.6 · IC025 +3.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 11.4 · ♀ 74% (drug 51%) | no trial data cached |
| Seizure | 357 | 16.4 14.8–18.1ROR 17.9 · χ² 5,158 / p <1e-300 | 16.3 EB05 15.0 · IC025 +3.8 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 11.9 | no trial data cached |
| Drug toxicity | 41 | 15.6 11.5–21.2ROR 15.8 · χ² 546 / p 5e-121 | 15.4 EB05 11.7 · IC025 +3.2 3/3 methods agree | Labeled (related wording) related wording | serious PRR 10.5 · 97% clinician | no trial data cached |
| Erythema multiforme | 26 | 14.7 10.0–21.6ROR 14.8 · χ² 317 / p 3e-71 | 14.3 EB05 9.9 · IC025 +2.9 3/3 methods agree | Not in label — unassessed | serious PRR 9.7 · ♀ 87% (drug 51%) | no trial data cached |
| Generalised tonic-clonic seizure | 44 | 14.2 10.6–19.0ROR 14.3 · χ² 524 / p 2e-116 | 13.9 EB05 10.7 · IC025 +3.1 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 10.0 | no trial data cached |
| Pharmaceutical product complaint | 64 | 12.8 10.0–16.3ROR 13.0 · χ² 684 / p 6e-151 | 12.6 EB05 10.1 · IC025 +3.1 3/3 methods agree | Not in label — unassessed | serious PRR 12.6 | no trial data cached |
| Drug level increased | 40 | 12.7 9.3–17.3ROR 12.8 · χ² 420 / p 2e-93 | 12.4 EB05 9.3 · IC025 +2.9 3/3 methods agree | Reporting / coding artifact | serious PRR 7.8 · ♀ 30% (drug 51%) | no trial data cached |
| Dysarthria (slurred speech) | 63 | 8.8 6.9–11.3ROR 8.9 · χ² 429 / p 2e-95 | 8.5 EB05 6.8 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious PRR 6.6 | no trial data cached |
| Drug interaction | 260 | 8.6 7.7–9.7ROR 9.2 · χ² 1,755 / p <1e-300 | 8.5 EB05 7.7 · IC025 +2.9 3/3 methods agree | Reporting / coding artifact | serious PRR 6.4 | no trial data cached |
| Toxicity to various agents | 238 | 7.5 6.6–8.4ROR 7.9 · χ² 1,334 / p 2e-292 | 7.4 EB05 6.6 · IC025 +2.7 3/3 methods agree | Not in label — unassessed | serious PRR 5.3 · 92% clinician | no trial data cached |
| Coordination abnormal | 18 | 6.7 4.3–10.7ROR 6.8 · χ² 82 / p 6e-20 | 5.9 EB05 3.9 · IC025 +1.8 3/3 methods agree | Labeled (related wording) related wording | serious PRR 5.8 | no trial data cached |
| Haematotoxicity | 11 | 6.2 3.5–11.3ROR 6.3 · χ² 43 / p 2e-11 | 5.1 EB05 3.0 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 4.5 | no trial data cached |
| Psychomotor hyperactivity | 19 | 6.0 3.8–9.4ROR 6.0 · χ² 74 / p 4e-18 | 5.3 EB05 3.6 · IC025 +1.6 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious PRR 6.9 | no trial data cached |
| Neurotoxicity | 19 | 5.8 3.7–9.0ROR 5.8 · χ² 70 / p 3e-17 | 5.1 EB05 3.4 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 4.0 | no trial data cached |
| Myoclonus | 13 | 5.7 3.3–9.9ROR 5.8 · χ² 46 / p 5e-12 | 4.8 EB05 3.0 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 4.2 | no trial data cached |
| Toxic skin eruption | 11 | 5.7 3.2–10.3ROR 5.7 · χ² 38 / p 3e-10 | 4.7 EB05 2.8 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 4.0 | no trial data cached |
| Eosinophilia | 19 | 5.7 3.7–9.0ROR 5.7 · χ² 69 / p 4e-17 | 5.1 EB05 3.4 · IC025 +1.6 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.2 | no trial data cached |
| Rash maculo-papular | 24 | 5.7 3.8–8.5ROR 5.7 · χ² 88 / p 3e-21 | 5.2 EB05 3.7 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 4.0 | no trial data cached |
| Drug eruption | 19 | 5.7 3.6–8.9ROR 5.7 · χ² 68 / p 6e-17 | 5.0 EB05 3.4 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 3.8 | no trial data cached |
| Bradycardia (slow heart rate) | 57 | 5.6 4.4–7.3ROR 5.7 · χ² 213 / p 1e-48 | 5.4 EB05 4.3 · IC025 +2.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.1 · 96% clinician | no trial data cached |
| Subdural haematoma | 15 | 5.5 3.3–9.1ROR 5.5 · χ² 51 / p 5e-13 | 4.8 EB05 3.1 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 3.8 | no trial data cached |
| Diplopia (double vision) | 26 | 5.3 3.6–7.7ROR 5.3 · χ² 86 / p 1e-20 | 4.8 EB05 3.5 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 4.6 | no trial data cached |
| Head injury | 30 | 5.0 3.5–7.1ROR 5.0 · χ² 92 / p 4e-22 | 4.7 EB05 3.4 · IC025 +1.6 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.7 | no trial data cached |
| Dyskinesia (involuntary movements) | 36 | 4.7 3.4–6.5ROR 4.7 · χ² 100 / p 7e-24 | 4.4 EB05 3.3 · IC025 +1.6 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.2 | no trial data cached |
| Hypomagnesaemia | 12 | 4.5 2.6–8.0ROR 4.6 · χ² 30 / p 2e-8 | 3.9 EB05 2.4 · IC025 +1.0 3/3 methods agree | Not in label — unassessed | serious PRR 3.3 | no trial data cached |
| Mydriasis | 11 | 4.5 2.5–8.1ROR 4.5 · χ² 27 / p 1e-7 | 3.9 EB05 2.3 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 3.3 | no trial data cached |
| Ventricular tachycardia | 14 | 4.4 2.6–7.5ROR 4.5 · χ² 34 / p 3e-9 | 3.9 EB05 2.5 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious PRR 3.1 | no trial data cached |
| Drug ineffective for unapproved indication | 47 | 4.4 3.3–5.9ROR 4.5 · χ² 122 / p 1e-28 | 4.3 EB05 3.3 · IC025 +1.6 3/3 methods agree | Reporting / coding artifact | serious PRR 6.3 · 94% clinician | no trial data cached |
| Product substitution issue | 48 | 4.4 3.3–5.8ROR 4.4 · χ² 122 / p 1e-28 | 4.2 EB05 3.3 · IC025 +1.6 3/3 methods agree | Reporting / coding artifact | serious PRR 5.1 | no trial data cached |
| Balance disorder | 72 | 4.4 3.5–5.5ROR 4.4 · χ² 185 / p 2e-42 | 4.3 EB05 3.5 · IC025 +1.7 3/3 methods agree | Labeled (related wording) related wording | serious PRR 4.4 | no trial data cached |
| Gamma-glutamyltransferase increased | 18 | 4.3 2.7–6.8ROR 4.3 · χ² 42 / p 5e-11 | 3.9 EB05 2.6 · IC025 +1.2 3/3 methods agree | Lab value / disease marker | serious PRR 3.1 | no trial data cached |
| Cardiomegaly | 10 | 4.2 2.3–7.9ROR 4.2 · χ² 22 / p 2e-6 | 3.6 EB05 2.1 · IC025 +0.8 3/3 methods agree | Not in label — unassessed | serious PRR 3.0 | 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 |
|---|---|---|---|---|---|---|
| Drug ineffective (drug did not work) | 624 | 2.5 2.3–2.7ROR 2.8 · χ² 593 / p 3e-131 | 2.5 EB05 2.3 · IC025 +1.2 3/3 methods agree | Reporting / coding artifact | serious PRR 3.1 | no trial data cached |
| Seizure | 357 | 16.4 14.8–18.1ROR 17.9 · χ² 5,158 / p <1e-300 | 16.3 EB05 15.0 · IC025 +3.8 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 11.9 | no trial data cached |
| Convulsion (seizure) | 289 | 26.3 23.5–29.4ROR 28.3 · χ² 6,996 / p <1e-300 | 26.1 EB05 23.7 · IC025 +4.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 18.1 | no trial data cached |
| Drug interaction | 260 | 8.6 7.7–9.7ROR 9.2 · χ² 1,755 / p <1e-300 | 8.5 EB05 7.7 · IC025 +2.9 3/3 methods agree | Reporting / coding artifact | serious PRR 6.4 | no trial data cached |
| Toxicity to various agents | 238 | 7.5 6.6–8.4ROR 7.9 · χ² 1,334 / p 2e-292 | 7.4 EB05 6.6 · IC025 +2.7 3/3 methods agree | Not in label — unassessed | serious PRR 5.3 · 92% clinician | no trial data cached |
| Epilepsy | 124 | 21.4 18.0–25.5ROR 22.1 · χ² 2,389 / p <1e-300 | 21.3 EB05 18.3 · IC025 +4.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 14.8 | no trial data cached |
| Hypotension (low blood pressure) | 113 | 3.0 2.5–3.6ROR 3.0 · χ² 147 / p 5e-34 | 2.9 EB05 2.5 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 2.4 | no trial data cached |
| Ataxia | 112 | 49.9 41.5–59.9ROR 51.3 · χ² 5,265 / p <1e-300 | 49.0 EB05 41.8 · IC025 +5.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 35.6 · 92% clinician | no trial data cached |
| Drug hypersensitivity | 109 | 3.0 2.5–3.6ROR 3.0 · χ² 140 / p 1e-32 | 2.9 EB05 2.5 · IC025 +1.2 3/3 methods agree | Labeled (related wording) related wording | serious PRR 2.7 | no trial data cached |
| Somnolence (drowsiness) | 100 | 2.6 2.2–3.2ROR 2.7 · χ² 99 / p 1e-23 | 2.6 EB05 2.2 · IC025 +1.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.9 | no trial data cached |
| Status epilepticus | 100 | 46.8 38.6–56.9ROR 48.0 · χ² 4,404 / p <1e-300 | 46.1 EB05 39.0 · IC025 +4.9 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 32.4 | no trial data cached |
| Confusional state (confusion) | 98 | 3.2 2.6–3.9ROR 3.2 · χ² 146 / p 8e-34 | 3.1 EB05 2.7 · IC025 +1.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.8 | no trial data cached |
| Drug reaction with eosinophilia and systemic symptoms | 92 | 19.0 15.5–23.2ROR 19.4 · χ² 1,546 / p <1e-300 | 18.9 EB05 15.8 · IC025 +3.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 13.2 · 96% clinician | no trial data cached |
| Stevens-johnson syndrome (severe blistering skin reaction) | 79 | 18.7 15.0–23.3ROR 19.1 · χ² 1,302 / p 2e-285 | 18.6 EB05 15.4 · IC025 +3.7 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 13.1 | no trial data cached |
| Tremor (shaking) | 72 | 2.3 1.8–2.9ROR 2.3 · χ² 51 / p 6e-13 | 2.3 EB05 1.9 · IC025 +0.8 | Labeled adverse reaction exact term | serious PRR 2.3 | 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.
- Grand mal convulsion — n=60, PRR 33.9
- Erythema multiforme — n=26, PRR 14.7
- Pharmaceutical product complaint — n=64, PRR 12.8
- Dysarthria — n=63, PRR 8.8
- Toxicity to various agents — n=238, PRR 7.5
- Rash maculo-papular — n=24, PRR 5.7
- Diplopia — n=26, PRR 5.3
✓ A hand-written Bradford Hill causality assessment exists for this drug: Phenytoin ↔ Stevens–Johnson syndrome / TEN.
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 Phenytoin?
In FDA FAERS, the most frequently co-reported reaction terms for Phenytoin are seizure, convulsion, toxicity to various agents, epilepsy, hypotension, ataxia. 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 Phenytoin have an FDA boxed warning?
No. The FDA label retrieved for Phenytoin has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Phenytoin 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 08a9d26b-4419-43ec-98f3-43d4534c2e76, effective 20260429; matched on
openfda.generic_name.exact:"PHENYTOIN") - 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, 183 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.