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What Is Phenobarbital?

Phenobarbital is a prescription barbiturate medication used as an anticonvulsant and sedative. It has been used for decades to manage certain seizure disorders, including generalized and focal seizures, and has additional uses in selected medical settings. Phenobarbital is available in oral and injectable formulations. It acts on the central nervous system to reduce excessive nerve activity. In the United States, phenobarbital is a Schedule IV controlled substance because repeated use can cause tolerance, physical dependence, and withdrawal symptoms. Treatment requires individualized dosing and monitoring.

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What Is Phenobarbital?

Phenobarbital is a prescription barbiturate medication used as an anticonvulsant and sedative. It has been used for decades to manage certain seizure disorders, including generalized and focal seizures, and has additional uses in selected medical settings. Phenobarbital is available in oral and injectable formulations. It acts on the central nervous system to reduce excessive nerve activity. In the United States, phenobarbital is a Schedule IV controlled substance because repeated use can cause tolerance, physical dependence, and withdrawal symptoms. Treatment requires individualized dosing and monitoring.

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How Does Phenobarbital Work?

Phenobarbital increases inhibitory activity at gamma-aminobutyric acid type A receptors in the brain. It prolongs the opening of chloride channels associated with these receptors, making neurons less likely to generate excessive electrical activity. This mechanism contributes to its antiseizure and sedating effects. At high concentrations, phenobarbital can produce substantial central nervous system depression, including impaired breathing. It also increases the activity of certain liver enzymes, which can change how other medications are metabolized. Its effects can persist because the medication has a long elimination half-life.

What Conditions Does Phenobarbital Treat?

Phenobarbital tablets are indicated for use as a sedative and for the treatment of generalized and partial seizures. Injectable phenobarbital also has uses in selected seizure emergencies and other supervised medical settings, depending on the product. Clinicians may choose phenobarbital when other antiseizure options are unsuitable or when a patient's clinical circumstances support its use. It is not appropriate for every seizure syndrome or sleep-related problem. Patients with porphyria, marked liver impairment, or certain serious respiratory conditions should not receive phenobarbital under its prescribing contraindications.

How Should Phenobarbital Be Taken?

Phenobarbital dosing depends on the indication, age, body weight, liver function, and response. Adult anticonvulsant treatment can involve approximately 60 mg to 200 mg daily, with doses individualized according to seizure control and tolerability. Children generally receive weight-based regimens. Blood concentration monitoring may be used to guide therapy, particularly during long-term treatment or when interacting medications are prescribed. Phenobarbital can cause substantial sleepiness and impaired coordination. Patients should not change their dose or stop treatment abruptly because withdrawal can trigger serious or prolonged seizures.

What Are the Side Effects and Warnings of Phenobarbital?

Common side effects include drowsiness, dizziness, impaired coordination, and slowed thinking. Serious risks include respiratory depression, profound sedation, allergic reactions, severe skin reactions, and physical dependence. Abrupt discontinuation after long-term use can cause withdrawal, including seizures and potentially life-threatening complications. Phenobarbital can reduce the effectiveness of hormonal contraceptives and interact with numerous other medications through liver enzyme induction. Alcohol, opioids, and other sedatives increase the risk of dangerous central nervous system depression. Patients should seek urgent care for breathing difficulties, severe rash, or unresponsiveness.

Common Questions About Phenobarbital

Is phenobarbital a barbiturate?

Yes. Phenobarbital is a long-acting barbiturate used as an anticonvulsant and sedative.

Can phenobarbital treat epilepsy?

Yes. Phenobarbital is used to control certain generalized and focal seizures. Its suitability depends on the seizure disorder and patient characteristics.

Is phenobarbital a controlled substance?

Yes. Phenobarbital is classified as a Schedule IV controlled substance in the United States because of its potential for misuse and dependence.

Can phenobarbital affect hormonal birth control?

Yes. Phenobarbital induces liver enzymes that can reduce the effectiveness of certain hormonal contraceptives. Patients should discuss appropriate contraception with their clinician.

References

DailyMed - PHENOBARBITAL tablet. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=884f7b62-160a-46c3-92d4-1031b255b76c. Date Accessed October 30, 2026.

Phenobarbital. LiverTox. https://www.ncbi.nlm.nih.gov/books/NBK548269/. Date Accessed October 30, 2026.

Phenobarbital. MedlinePlus. https://medlineplus.gov/druginfo/meds/a682007.html. Date Accessed October 30, 2026.

Phenobarbital. PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/Phenobarbital. Date Accessed October 30, 2026.

Phenobarbital. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK532277/. Date Accessed October 30, 2026.