Phenobarbital

Raw research findings for this medication. Mostly single studies, not curated or confirmed robust.

About Phenobarbital

What it is

Phenobarbital is a barbiturate and one of the oldest anticonvulsants still in use. It strengthens the calming effect of GABA in the brain. It is used for many types of seizures, for prolonged seizures in hospital, for seizures in newborns, and in some settings for alcohol withdrawal. It strongly speeds up many liver enzymes. It is sold as Luminal, among other names.

How genes come into it

Phenobarbital is broken down mainly by CYP2C9 and CYP2C19, and studies have looked at CYP2C19 variants for its clearance. Most gene studies on it looked at the transporter ABCB1, which pumps medicines out of the brain, for drug-resistant epilepsy, with mixed results. There is no CPIC or DPWG guideline.

What research found

Every published finding on gene variants and Phenobarbital. Upload your DNA file to see which of these rows apply to you.

Rated evidence (5 rated variants)

PharmGKB weighs all studies of a variant and rates how strong the evidence is, from 1A (strongest) to 4.

CYP1A1 rs2606345: Level 3. Efficacy: Epilepsy. 2.

HLA-B HLA-B*51:01: Level 3. Toxicity: Stevens-Johnson Syndrome. 1.

ABCB1 rs1045642: Level 3. Efficacy: Epilepsy. 1.

MTHFR rs1801133: Level 3. Toxicity: Epilepsy, Psychotic Disorder. 1.

Metabolism (2 findings)

Studies of how quickly the body processes this medication.

CYP2C19 CYP2C19*1, CYP2C19*2, CYP2C19*3: CYP2C19 *2/*2 + *2/*3 (assigned as poor metabolizer phenotype) is not associated with metabolism of phenobarbital in infants with Seizures as compared to CYP2C19 *1/*1 (assigned as normal metabolizer phenotype) .

CYP2C19 CYP2C19*1, CYP2C19*2, CYP2C19*3: CYP2C19 *2/*2 + *2/*3 (assigned as poor metabolizer phenotype) is not associated with metabolism of phenobarbital in infants with Seizures as compared to CYP2C19 *1/*1 (assigned as normal metabolizer phenotype) .

Response (10 findings)

Studies of how well it worked in people carrying a variant.

ABCB1 rs1045642: Genotype GG is associated with increased resistance to phenobarbital in people with Epilepsy as compared to genotype AA.

SCN2A rs17183814: Allele A is associated with resistance to carbamazepine, phenobarbital, phenytoin or valproic acid as compared to allele G.

ABCB1 rs1045642: Allele A is not associated with increased response to carbamazepine, phenobarbital, phenytoin and valproic acid in people with Epilepsy as compared to allele G.

ABCB1 rs1045642: Allele G is not associated with response to carbamazepine, phenobarbital, phenytoin or valproic acid in people with Epilepsy as compared to allele A.

Study findings and evidence levels: PharmGKB (CC BY-SA 4.0). Guidelines: CPIC and DPWG, as bundled in PharmCAT. Most studies were done mainly in people of European ancestry.

Related Drugs

More drugs from the same category

Mysoline (Barbiturates)

Abilify (Antipsychotics)

Adderall (Stimulants)

Not a prescribing recommendation. This page is educational information about pharmacogenomic research and clinical guidelines - it is not medical or dosing advice, and not a prediction of how any medication will work for you. Never start, stop, or change a medication or dose based on it; talk to your doctor or pharmacist, who can order clinical-grade testing if appropriate.

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Content updated September 2026.

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