Phenobarbital side effects: what 14,407 FDA adverse event reports show

Phenobarbital · 1,118 reaction terms · 51,263 drug–reaction co-reports · data 2026-09-14

Drug class

Not stated in label

Who reports

14,407 reports · 85% serious · 1,777 with death outcome · 54% female

openFDA FAERS counts, all years, deduplication not applied

Used for

A. Sedative B. Anticonvulsant–For the treatment of generalized and partial seizures.

FDA label, Indications and Usage

What it is

DESCRIPTION The barbiturates are nonselective central nervous system (CNS) depressants that are primarily used as sedative-hypnotics. In sub-hypnotic doses, they are also used as anticonvulsants. The barbiturates and their sodium salts are subject to control under the Federal Controlled Substances Act.

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) 1Likely indication confounding 4Reporting / coding artifact 4Lab value / disease marker 7Not in label — unassessed 24

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.
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. 1,078 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.

Show: hide coding/lab/outcome terms hide indication terms unlabeled only hide PRR-only

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Porphyrins stool increased	12	2,870.6 1,077.5–7,647.5ROR 2,873.0 · χ² 10,537 / p <1e-300	378.4 EB05 230.7 · IC025 +3.6 3/3 methods agree	Lab value / disease marker	serious n=12	not reported in cached trials
Ultrasound ovary abnormal	11	1,315.7 580.6–2,981.3ROR 1,316.7 · χ² 6,869 / p <1e-300	313.0 EB05 186.5 · IC025 +3.5 3/3 methods agree	Not in label — unassessed	serious n=11	not reported in cached trials
Urine copper increased	13	691.1 356.7–1,339.0ROR 691.7 · χ² 5,589 / p <1e-300	276.9 EB05 172.2 · IC025 +3.7 3/3 methods agree	Lab value / disease marker	serious n=13	not reported in cached trials
Developmental glaucoma	20	637.9 376.8–1,080.0ROR 638.8 · χ² 8,369 / p <1e-300	310.6 EB05 212.3 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious n=20	not reported in cached trials
New onset refractory status epilepticus	29	547.7 357.2–839.8ROR 548.8 · χ² 11,062 / p <1e-300	314.4 EB05 229.6 · IC025 +5.1 3/3 methods agree	Not in label — unassessed	serious n=29 · ♀ 0% (drug 54%) · 100% clinician	not reported in cached trials
Angiofibroma	17	428.1 249.1–735.6ROR 428.6 · χ² 5,255 / p <1e-300	240.8 EB05 159.3 · IC025 +4.2 3/3 methods agree	Not in label — unassessed	serious n=17	not reported in cached trials
Intra-abdominal pressure increased	35	418.6 287.4–609.8ROR 419.6 · χ² 10,968 / p <1e-300	275.5 EB05 207.1 · IC025 +5.3 3/3 methods agree	Lab value / disease marker	serious n=35 · ♀ 100% (drug 54%)	not reported in cached trials
Victim of child abuse	48	351.5 256.5–481.8ROR 352.7 · χ² 13,196 / p <1e-300	254.0 EB05 199.2 · IC025 +5.7 3/3 methods agree	Reporting / coding artifact	serious n=48 · ♀ 0% (drug 54%)	not reported in cached trials
Child abuse	45	319.7 231.6–441.5ROR 320.7 · χ² 11,434 / p <1e-300	235.6 EB05 183.3 · IC025 +5.6 3/3 methods agree	Reporting / coding artifact	serious n=45 · ♀ 0% (drug 54%)	not reported in cached trials
Epidural lipomatosis	55	273.2 204.8–364.3ROR 274.2 · χ² 12,302 / p <1e-300	212.7 EB05 169.6 · IC025 +5.8 3/3 methods agree	Not in label — unassessed	serious n=55 · ♀ 0% (drug 54%) · 91% clinician	not reported in cached trials
Multiple-drug resistance	462	255.8 232.0–282.1ROR 264.3 · χ² 99,328 / p <1e-300	215.3 EB05 199.4 · IC025 +7.3 3/3 methods agree	Reporting / coding artifact	serious n=351 · 98% clinician	not reported in cached trials
Necrosis ischaemic	56	200.4 151.6–265.0ROR 201.2 · χ² 9,577 / p <1e-300	166.1 EB05 132.7 · IC025 +5.7 3/3 methods agree	Not in label — unassessed	serious n=56	not reported in cached trials
Myocardial depression	27	184.5 123.7–275.4ROR 184.9 · χ² 4,206 / p <1e-300	146.8 EB05 106.0 · IC025 +4.7 3/3 methods agree	Not in label — unassessed	serious n=27 · ♀ 100% (drug 54%) · 100% clinician	not reported in cached trials
Lymphangioleiomyomatosis	12	179.4 98.5–326.9ROR 179.6 · χ² 1,737 / p <1e-300	127.7 EB05 77.8 · IC025 +3.5 3/3 methods agree	Not in label — unassessed	serious n=12	not reported in cached trials
Oropharyngeal oedema	13	143.5 81.2–253.8ROR 143.7 · χ² 1,546 / p <1e-300	109.9 EB05 68.4 · IC025 +3.6 3/3 methods agree	Not in label — unassessed	serious n=12	not reported in cached trials
Infantile spasms	58	128.5 98.3–168.0ROR 129.0 · χ² 6,617 / p <1e-300	113.7 EB05 91.2 · IC025 +5.4 3/3 methods agree	Not in label — unassessed	serious n=58	not reported in cached trials
Pneumatosis	35	124.3 88.1–175.6ROR 124.6 · χ² 3,828 / p <1e-300	107.9 EB05 81.1 · IC025 +4.9 3/3 methods agree	Not in label — unassessed	serious n=35 · ♀ 100% (drug 54%)	not reported in cached trials
Congenital aplasia	22	119.6 77.4–184.7ROR 119.8 · χ² 2,280 / p <1e-300	101.0 EB05 70.3 · IC025 +4.3 3/3 methods agree	Not in label — unassessed	serious n=22	not reported in cached trials
Anticonvulsant drug level above therapeutic	48	115.6 86.2–155.0ROR 116.0 · χ² 4,941 / p <1e-300	102.8 EB05 80.6 · IC025 +5.2 3/3 methods agree	Lab value / disease marker	serious n=47 · ♀ 30% (drug 54%)	not reported in cached trials
Intensive care unit acquired weakness	27	110.7 74.9–163.7ROR 110.9 · χ² 2,625 / p <1e-300	96.1 EB05 69.3 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious n=27 · ♀ 0% (drug 54%) · 100% clinician	not reported in cached trials
Angiomyolipoma	14	101.0 58.7–173.6ROR 101.1 · χ² 1,203 / p 7e-264	83.9 EB05 53.1 · IC025 +3.6 3/3 methods agree	Not in label — unassessed	serious n=14	not reported in cached trials
Epileptic encephalopathy	14	98.5 57.3–169.2ROR 98.6 · χ² 1,175 / p 9e-258	82.2 EB05 52.1 · IC025 +3.6 3/3 methods agree	Not in label — unassessed	serious n=14	not reported in cached trials
Multiple drug therapy	38	83.8 60.4–116.2ROR 84.0 · χ² 2,859 / p <1e-300	76.3 EB05 58.0 · IC025 +4.8 3/3 methods agree	Reporting / coding artifact	serious n=38 · ♀ 100% (drug 54%) · 92% clinician	not reported in cached trials
Neonatal seizure	13	79.1 45.2–138.2ROR 79.1 · χ² 877 / p 5e-193	67.8 EB05 42.2 · IC025 +3.4 3/3 methods agree	Likely indication confounding shares a disease stem with the indications wording	serious n=13	not reported in cached trials
Myoclonic epilepsy	72	74.8 59.0–94.7ROR 75.1 · χ² 4,912 / p <1e-300	69.9 EB05 57.3 · IC025 +5.2 3/3 methods agree	Not in label — unassessed	serious n=71	not reported in cached trials
Anticonvulsant drug level increased	78	73.3 58.4–91.9ROR 73.7 · χ² 5,222 / p <1e-300	68.6 EB05 56.8 · IC025 +5.2 3/3 methods agree	Lab value / disease marker	serious n=72	not reported in cached trials
Partial seizures with secondary generalisation	22	71.6 46.7–109.8ROR 71.7 · χ² 1,392 / p <1e-300	64.6 EB05 45.0 · IC025 +4.1 3/3 methods agree	Likely indication confounding shares a disease stem with the indications wording	serious n=22	not reported in cached trials
Seizure cluster	37	70.2 50.5–97.5ROR 70.3 · χ² 2,339 / p <1e-300	64.8 EB05 49.1 · IC025 +4.6 3/3 methods agree	Likely indication confounding shares a disease stem with the indications wording	serious n=35	not reported in cached trials
Status epilepticus	512	69.0 63.2–75.2ROR 71.5 · χ² 32,673 / p <1e-300	65.7 EB05 61.1 · IC025 +5.8 3/3 methods agree	Not in label — unassessed	serious PRR 44.8	not reported in cached trials
Tonic convulsion	63	68.5 53.2–88.1ROR 68.7 · χ² 3,933 / p <1e-300	64.2 EB05 51.9 · IC025 +5.0 3/3 methods agree	Not in label — unassessed	serious n=63	not reported in cached trials
Lennox-gastaut syndrome	10	67.7 35.9–127.6ROR 67.7 · χ² 565 / p 3e-125	57.9 EB05 33.6 · IC025 +2.9 3/3 methods agree	Not in label — unassessed	serious n=10	not reported in cached trials
Breast hyperplasia	15	64.5 38.4–108.1ROR 64.5 · χ² 837 / p 2e-184	57.5 EB05 37.0 · IC025 +3.5 3/3 methods agree	Not in label — unassessed	serious n=15	not reported in cached trials
Necrotising enterocolitis neonatal	17	64.2 39.5–104.4ROR 64.3 · χ² 953 / p 2e-209	57.7 EB05 38.2 · IC025 +3.7 3/3 methods agree	Not in label — unassessed	serious n=17	not reported in cached trials
Anticonvulsant drug level below therapeutic	32	63.8 44.8–90.9ROR 63.9 · χ² 1,834 / p <1e-300	59.1 EB05 43.8 · IC025 +4.4 3/3 methods agree	Lab value / disease marker	serious n=31	not reported in cached trials
Anticonvulsant drug level decreased	59	62.7 48.4–81.4ROR 63.0 · χ² 3,375 / p <1e-300	59.1 EB05 47.5 · IC025 +4.9 3/3 methods agree	Lab value / disease marker	serious n=56	not reported in cached trials
Intraventricular haemorrhage neonatal	20	62.1 39.7–97.2ROR 62.2 · χ² 1,095 / p 2e-240	56.6 EB05 38.7 · IC025 +3.9 3/3 methods agree	Not in label — unassessed	serious n=20	not reported in cached trials
Cytomegalovirus hepatitis	14	60.0 35.2–102.4ROR 60.0 · χ² 724 / p 1e-159	53.6 EB05 34.0 · IC025 +3.4 3/3 methods agree	Not in label — unassessed	serious n=14	not reported in cached trials
Cerebellar atrophy	35	59.9 42.8–84.0ROR 60.1 · χ² 1,891 / p <1e-300	55.9 EB05 42.0 · IC025 +4.4 3/3 methods agree	Not in label — unassessed	serious n=35	not reported in cached trials
Drug withdrawal convulsions	70	59.4 46.8–75.4ROR 59.7 · χ² 3,803 / p <1e-300	56.2 EB05 46.0 · IC025 +5.0 3/3 methods agree	Labeled (related wording) related wording	serious n=69	not reported in cached trials
Atonic seizures	31	58.9 41.1–84.3ROR 59.0 · χ² 1,638 / p <1e-300	54.8 EB05 40.4 · IC025 +4.3 3/3 methods agree	Likely indication confounding shares a disease stem with the indications wording	serious n=29	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 Phenobarbital 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).

NCT01720667 — Efficacy of Intravenous Levetiracetam in Neonatal Seizures (N=280, PHASE1, PHASE2; 11 AE terms posted; arms: Intravenous Phenobarbital; Intravenous Levetiracetam)

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
Drug ineffective (drug did not work)	2,449	2.7 2.6–2.8ROR 3.1 · χ² 2,813 / p <1e-300	2.7 EB05 2.6 · IC025 +1.4 3/3 methods agree	Reporting / coding artifact	serious PRR 4.7	not reported in cached trials
Seizure	1,601	20.6 19.6–21.6ROR 23.0 · χ² 29,546 / p <1e-300	20.3 EB05 19.5 · IC025 +4.3 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 13.6	not reported in cached trials
Off label use (used outside approved label)	1,431	2.4 2.3–2.5ROR 2.6 · χ² 1,219 / p 3e-267	2.4 EB05 2.3 · IC025 +1.2 3/3 methods agree	Reporting / coding artifact	serious PRR 2.7	not reported in cached trials
Drug interaction	645	5.9 5.5–6.4ROR 6.2 · χ² 2,652 / p <1e-300	5.9 EB05 5.5 · IC025 +2.4 3/3 methods agree	Reporting / coding artifact	serious PRR 4.2	not reported in cached trials
Toxicity to various agents	636	5.5 5.1–6.0ROR 5.7 · χ² 2,367 / p <1e-300	5.5 EB05 5.1 · IC025 +2.3 3/3 methods agree	Not in label — unassessed	serious PRR 3.8 · 91% clinician	not reported in cached trials
Status epilepticus	512	69.0 63.2–75.2ROR 71.5 · χ² 32,673 / p <1e-300	65.7 EB05 61.1 · IC025 +5.8 3/3 methods agree	Not in label — unassessed	serious PRR 44.8	not reported in cached trials
Multiple-drug resistance	462	255.8 232.0–282.1ROR 264.3 · χ² 99,328 / p <1e-300	215.3 EB05 199.4 · IC025 +7.3 3/3 methods agree	Reporting / coding artifact	serious n=351 · 98% clinician	not reported in cached trials
Somnolence (drowsiness)	459	3.3 3.0–3.6ROR 3.4 · χ² 751 / p 1e-165	3.3 EB05 3.1 · IC025 +1.6 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 3.1	not reported in cached trials
Condition aggravated	429	2.1 1.9–2.3ROR 2.1 · χ² 239 / p 3e-54	2.1 EB05 1.9 · IC025 +0.9	Reporting / coding artifact	serious PRR 2.0	not reported in cached trials
Epilepsy	424	20.5 18.6–22.5ROR 21.1 · χ² 7,744 / p <1e-300	20.2 EB05 18.6 · IC025 +4.1 3/3 methods agree	Not in label — unassessed	serious PRR 13.8	not reported in cached trials
Fall	409	1.8 1.6–2.0ROR 1.8 · χ² 144 / p 1e-33	1.8 EB05 1.6 · IC025 +0.7	Not in label — unassessed	serious PRR 1.4	not reported in cached trials
Hypotension (low blood pressure)	402	2.9 2.7–3.2ROR 3.0 · χ² 511 / p 2e-113	2.9 EB05 2.7 · IC025 +1.4 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 2.3	NCT01720667: 4/42 (9.5%) on Phenobarbital (serious AE)
Pyrexia (fever)	387	1.6 1.5–1.8ROR 1.6 · χ² 94 / p 1e-22	1.6 EB05 1.5 · IC025 +0.5	Labeled (related wording) related wording	serious PRR 1.3	not reported in cached trials
Product use in unapproved indication	384	2.3 2.1–2.5ROR 2.3 · χ² 281 / p 3e-63	2.3 EB05 2.1 · IC025 +1.0 3/3 methods agree	Reporting / coding artifact	serious PRR 3.1	not reported in cached trials
Convulsion (seizure)	369	9.3 8.4–10.3ROR 9.5 · χ² 2,720 / p <1e-300	9.2 EB05 8.4 · IC025 +3.0 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 6.4	not reported in cached trials

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.

Developmental glaucoma — n=20, PRR 637.9
New onset refractory status epilepticus — n=29, PRR 547.7
Epidural lipomatosis — n=55, PRR 273.2
Necrosis ischaemic — n=56, PRR 200.4
Myocardial depression — n=27, PRR 184.5
Infantile spasms — n=58, PRR 128.5
Pneumatosis — n=35, PRR 124.3
Congenital aplasia — n=22, PRR 119.6
Intensive care unit acquired weakness — n=27, PRR 110.7
Myoclonic epilepsy — n=72, PRR 74.8

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 Phenobarbital?

In FDA FAERS, the most frequently co-reported reaction terms for Phenobarbital are seizure, toxicity to various agents, status epilepticus, somnolence, epilepsy, fall. 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 Phenobarbital have an FDA boxed warning?

No. The FDA label retrieved for Phenobarbital has no boxed warning; see the label's Warnings and Precautions for the recognised risks.

Do FAERS signals prove that Phenobarbital 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 057992c1-29a0-4229-9c30-d787cb632eac, effective 20250922; matched on openfda.generic_name.exact:"PHENOBARBITAL")
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, field patient.drug.openfda.generic_name.exact, 1,118 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 PHENOBARBITAL, 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.