Phenobarbital

Pronunciation: fee-noh-BAR-bi-tal.

Generic name
phenobarbital (phenobarbitone)
Drug class
Barbiturate anticonvulsant and sedative-hypnotic
Form
Oral tablet (15 mg, 30 mg, 60 mg, 100 mg), oral solution/elixir, or injection
Route
Oral or intravenous (formulation-dependent)
Legal status
Prescription-only, controlled substance

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: PHENOBARB (6) · Full directory

What phenobarbital (phenobarbitone) is and how it works

Phenobarbital is a prescription barbiturate used mainly as a long-term anticonvulsant to control certain types of seizures, and sometimes as a short-term sedative. It is a controlled substance because of its potential for dependence. (1) (5)

Take phenobarbital exactly as your prescriber directs. Never change your dose or stop taking it on your own, even if you feel well -- doing so can trigger serious, potentially life-threatening withdrawal seizures. Any change must be planned and supervised by your prescriber.

Mechanism of action: how phenobarbital (phenobarbitone) works

Phenobarbital is a long-acting barbiturate that potentiates GABA-A-mediated synaptic inhibition in the central nervous system, raising the seizure threshold and limiting seizure spread; it also induces hepatic microsomal enzymes (CYP3A4, CYP2B6, CYP2C family), which underlies its many drug interactions. (3) (5)

What phenobarbital (phenobarbitone) is used for

Epilepsy and seizure control

Used for long-term treatment of generalised tonic-clonic seizures and partial (focal) seizures, and for prevention/treatment of febrile seizures. Effective for most seizure types except absence (petit mal) seizures. (3) (5)

Neonatal seizures (specific injectable product)

A modern FDA-approved intravenous formulation (SEZABY) is used specifically to treat seizures in newborn babies (term and preterm infants) in hospital settings. (1)

Sedation and other uses

Also used, less commonly today, for short-term relief of anxiety/tension, short-term treatment of insomnia, as preoperative sedation, and to help manage certain neonatal or hereditary conditions involving high bilirubin levels. (5) (7)

Before taking phenobarbital (phenobarbitone)

Do not take / not appropriate for

  • Do not take phenobarbital if you have acute porphyria (a group of rare blood disorders) -- it can trigger a life-threatening attack. (all countries) (3) (5)
  • Do not take phenobarbital if you have had a serious allergic reaction to it or to other barbiturates. (all countries) (2) (3)
  • Phenobarbital is generally avoided in people with severe respiratory disease, severe liver impairment, or severe kidney impairment, unless your prescriber judges the benefit outweighs the risk. (all countries) (3) (5)

Tell your clinician about

  • Any personal or family history of porphyria.
  • Any history of drug or alcohol dependence.
  • Liver, kidney, or respiratory problems.
  • All other medicines you take, especially hormonal contraceptives, blood thinners (e.g. warfarin), other seizure medicines, or anything that makes you sleepy.
  • Pregnancy, plans for pregnancy, or breastfeeding.
  • Any history of low bone density, fractures, or osteoporosis.
(3) (5)

How to take phenobarbital (phenobarbitone)

  • Take exactly as your prescriber directs -- the dose and timing depend on the condition being treated, your age, and how your body responds.
  • Never change your dose, skip planned tapering steps, or stop taking phenobarbital on your own -- always follow your prescriber's plan, especially if you have been taking it for a while.
  • If your prescriber decides to stop your treatment, this will be done through a gradual, supervised taper to reduce the risk of withdrawal seizures.
  • Avoid alcohol and check with your prescriber before taking any other sedating medicine, since combining these with phenobarbital can be dangerous.
(2) (3)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6) (7)

Missed dose

Contact your prescriber or pharmacist for specific guidance if you miss a dose, since missing doses of an anticonvulsant can increase seizure risk and the right response depends on your regimen.

Overdose

Seek emergency medical help immediately if you suspect an overdose. Signs can include severe drowsiness, confusion, slow or shallow breathing, or unresponsiveness. This is a medical emergency. (3)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Drowsiness, lethargy, and residual sedation, especially early in treatment.

What to notice: Drowsiness, lethargy, and residual sedation, especially early in treatment.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Dizziness, unsteadiness (ataxia), and involuntary eye movements (nystagmus).

What to notice: Dizziness, unsteadiness (ataxia), and involuntary eye movements (nystagmus).

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (3)

In children, paradoxical hyperactivity or behavioural disturbance can occur; in older adults, memory and cognitive impairment.

What to notice: In children, paradoxical hyperactivity or behavioural disturbance can occur; in older adults, memory and cognitive impairment.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (3)

Nausea, headache.

What to notice: Nausea, headache.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Serious warnings

Signs of withdrawal after any dose reduction or missed doses following prolonged use — boxed_warning

Symptoms: Anxiety, tremor, sweating, weakness, dizziness, nausea (early); confusion, hallucinations, or seizures (later and more serious).

Action: Contact your prescriber immediately or seek emergency care for any seizure or severe confusion. Never attempt to restart, adjust, or stop phenobarbital yourself -- all dose changes must be planned and supervised by your prescriber as a gradual taper. (1) (3) (5)

Severe sedation or breathing problems, especially when combined with opioids, alcohol, or other sedatives — boxed_warning

Symptoms: Extreme drowsiness, slow or shallow breathing, unresponsiveness, blue-tinged lips or fingertips.

Action: Seek emergency medical help immediately. (1)

Signs of a serious skin reaction (Stevens-Johnson syndrome or toxic epidermal necrolysis) — emergency

Symptoms: Widespread rash, blistering, peeling skin, mouth/eye sores, or fever with a rash.

Action: Seek emergency medical help immediately and let a clinician decide about stopping the medicine, and follow emergency guidance if you are unwell -- these reactions can be fatal. (3) (5)

Signs of a porphyria attack — emergency

Symptoms: Severe abdominal pain, vomiting, confusion, or muscle weakness in someone with porphyria.

Action: Seek emergency medical help immediately. (3) (5)

New or worsening depression, unusual mood changes, or thoughts of self-harm — high caution

Symptoms: Suicidal thoughts or behaviour, or unusual changes in mood, are a recognised risk with anticonvulsant medicines as a class.

Action: Tell your prescriber or seek urgent help promptly if this occurs; caregivers should also watch for these changes. (3) (5)

Interactions

  • Phenobarbital is a strong hepatic enzyme inducer and can reduce the effectiveness of many other medicines, including hormonal contraceptives (may cause contraceptive failure), warfarin and other coumarin anticoagulants, corticosteroids, some antiepileptics (e.g. phenytoin, carbamazepine, lamotrigine), certain calcium channel blockers, theophylline, some antivirals and antiarrhythmics, and thyroid hormone replacement -- tell your prescriber about all medicines you take so doses can be adjusted appropriately. (3) (5)
  • Combining phenobarbital with alcohol, opioids, benzodiazepines, or other central nervous system depressants increases the risk of severe sedation and breathing problems. (1) (5)
  • St John's Wort (an herbal supplement) may reduce phenobarbital's effect. (3)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Phenobarbital crosses the placenta and has been associated with an increased risk of major congenital malformations; it should generally be avoided in the first and third trimesters unless considered essential. If it is being used to prevent seizures, it should not be stopped without medical guidance because of the risk of dangerous seizures during pregnancy. Vitamin K and folic acid supplementation may be recommended -- discuss with your prescriber. (1) (2) (3) (4) (5) (6) (7)

Breastfeeding

Phenobarbital passes into breast milk and can cause sedation or withdrawal effects in a breastfed infant; breastfeeding is generally not advised while taking it, but discuss your individual situation with your prescriber. (1) (2) (3) (4) (5) (6) (7)

Children

Used in children for seizure control and other approved indications, with doses adjusted by body weight; paradoxical hyperactivity or behavioural changes can occur in this age group. (1) (2) (3) (4) (5) (6) (7)

Elderly

Older adults may need lower doses and closer monitoring because of increased sensitivity to sedation, fall/fracture risk, and drug clearance changes. (1) (2) (3) (4) (5) (6) (7)

Hepatic_impairment

Use with caution; contraindicated in marked/severe hepatic impairment in some labels. (1) (2) (3) (4) (5) (6) (7)

Renal_impairment

Use with caution in renal impairment; contraindicated in severe renal impairment in some labels. (1) (2) (3) (4) (5) (6) (7)

Source_ids

US-FDA-SEZABY-PHENOBARBITAL-2022,UK-MHRA-PHENOBARBITAL-CLONMEL-2024,CA-HC-PHENOBARB-PENDOPHARM-2017 (1) (2) (3) (4) (5) (6) (7)

Monitoring

Before starting

  • Baseline liver and kidney function where relevant
  • Review of all current medicines for interactions
  • Screening for porphyria history

During treatment

  • Periodic review of seizure control and side effects.
  • Monitoring for signs of dependence, mood changes, or withdrawal risk, especially with long-term use.
  • Bone health monitoring with long-term use, given the association between long-term antiepileptic use and reduced bone density.
  • Blood level monitoring where clinically indicated, since phenobarbital has a long half-life and individual dosing needs vary.
(3) (5)

Storage

Store at 20-25C (68-77F), protected from light and moisture, in a tight, light-resistant container with a child-resistant closure. Keep securely stored and out of reach of children, given its controlled-substance status.

Study the drug class: Antiepileptics

Professional information

Clinician-facing context only, sourced from the current FDA SEZABY label, older US oral tablet labeling, and UK/Canadian regulatory sources; verify against the current full label before prescribing.

United Kingdom

Indication: Epilepsy (all forms except absence seizures)

Dose summary: Adults and the elderly: 60-180 mg daily at night. Children: 5-8 mg/kg bodyweight daily. Caution and careful monitoring advised in elderly patients.

Renal context: Contraindicated in severe renal impairment; caution advised otherwise. (3)

United States (older oral labeling)

Indication: Sedative, hypnotic, anticonvulsant

Dose summary: Sedative: 30-120 mg/day divided (adults); 6 mg/kg/day divided (children). Hypnotic: 100-320 mg (adults). Anticonvulsant: 50-100 mg 2-3 times daily (adults); 15-50 mg 2-3 times daily (children).

Renal context: Not detailed in this older label; use with caution in renal impairment per general barbiturate precautions. (2)

Mechanism of action

Hepatic guidance

Use with caution in hepatic impairment; contraindicated in marked/severe hepatic impairment per some labels. Enzyme induction can affect metabolism of numerous concurrently used drugs.

Overdose note

Overdose can cause drowsiness progressing to coma, respiratory depression, hypotension, and hypothermia; management includes supportive care, and in severe poisoning, charcoal haemoperfusion is considered the treatment of choice per the UK SmPC reviewed. (3) (5)

Frequently asked questions

Is phenobarbital available in the US, UK, Europe, Canada, Australia, and New Zealand?

Yes, phenobarbital remains authorised and supplied in all of these regions, though in the European Union it is authorised nationally in individual member states rather than through a single EU-wide approval. (1) (3) (4) (5) (6) (7)

Can I stop taking phenobarbital if I feel fine?

No. Never stop or reduce phenobarbital on your own, even if you feel well. Because your body can become physically dependent on it, stopping abruptly or too quickly can cause a dangerous, potentially life-threatening withdrawal reaction, including withdrawal seizures. Any change must be a gradual taper planned and supervised by your prescriber. (1) (3) (5)

Does phenobarbital affect my birth control pill or other medicines?

Yes. Phenobarbital strongly affects liver enzymes and can make hormonal contraceptives, warfarin, and several other medicines less effective. Tell your prescriber about every medicine you take, including contraception, so they can advise on additional precautions. (3) (5)

What is the mechanism of action of phenobarbital (phenobarbitone)?

Phenobarbital is a long-acting barbiturate that potentiates GABA-A-mediated synaptic inhibition in the central nervous system, raising the seizure threshold and limiting seizure spread; it also induces hepatic microsomal enzymes (CYP3A4, CYP2B6, CYP2C family), which underlies its many drug interactions. (3) (5)

What is the generic name of Phenobarbital?

The generic name is phenobarbital (phenobarbitone). (1) (5)

What class of drug is phenobarbital (phenobarbitone)?

Phenobarbital is classed as: Barbiturate anticonvulsant and sedative-hypnotic. (1) (5)

References

  1. SEZABY (phenobarbital sodium) injection -- full prescribing informationU.S. Food and Drug Administration / DailyMed (NIH), full prescribing information for SEZABY (phenobarbital sodium injection) · United States · dated 2025-12 · accessed 2026-07-30 · source 1
  2. Phenobarbital Tablets, USP -- prescribing informationU.S. Food and Drug Administration / DailyMed (NIH) -- older oral phenobarbital tablet labeling (marketed without a formal FDA safety/efficacy finding, consistent with many decades-old generic sedative/anticonvulsant products in the US) · United States · accessed 2026-07-30 · source 2
  3. Phenobarbital Tablets BP 30 mg -- Summary of Product CharacteristicsUK Medicines and Healthcare products Regulatory Agency (MHRA) -- Summary of Product Characteristics, Clonmel Healthcare · United Kingdom · accessed 2026-07-30 · source 3
  4. List of nationally authorised medicinal products -- active substance phenobarbital (PSUSA/00002370/202001)European Medicines Agency (EMA) -- list of nationally authorised medicinal products (PSUR single assessment procedure) · European Union · dated 2021 · accessed 2026-07-30 · source 4
  5. PHENOBARB (Phenobarbital Tablets USP) and PHENOBARB ELIXIR -- Product MonographHealth Canada product monograph, PENDOPHARM (Division of Pharmascience Inc.) · Canada · dated 2017-04-06 · accessed 2026-07-30 · source 5
  6. PHENOBARB phenobarbital 30mg tablet bottle -- ARTG registrationTherapeutic Goods Administration (TGA), Australia · Australia · dated 1991-10-14 · accessed 2026-07-30 · source 6
  7. Phenobarbitone (Noumed) 15 mg / 30 mg tablets -- New Zealand Data SheetMedsafe (New Zealand regulator) · New Zealand · accessed 2026-07-30 · source 7

Brand names by country

Single-ingredient phenobarbital (phenobarbitone) names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • SEZABY100 mg · sun pharmaceutical industries, inc.

United Kingdom

  • Phenobarbital Tablets BP 30 mg (3)MHRA licensed smpc confirmed · 30 mg · Clonmel Healthcare

Canada

  • PHENOBARB

Australia

  • PHENOBARB (6)TGA ARTG registered 1991 still active confirmed · 30 mg · Arrotex Pharmaceuticals Pty Ltd

New Zealand

  • Phenobarbitone (Noumed) (7)Medsafe approved confirmed · 15 mg, 30 mg · Noumed Pharmaceuticals
View brands in additional countries.

European Union

Luminal / BIALMINAL (national brands, no EMA centralised authorisation) (4)

This page provides general reference information about phenobarbital and is not a substitute for advice from the prescriber managing your treatment. All dosing and treatment decisions, especially any change in dose or stopping treatment, should be made with your prescriber.

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