What the FDA labels say about taking them together
Phenobarbital and tiagabine
Tiagabine's FDA label of September 30, 2021 names phenobarbital in its drug interactions section; phenobarbital's label does not name tiagabine itself but warns about its class (Anti-seizure medicines). The tiagabine label: “The tiagabine HCl dosing recommendations in current labeling for treatment of epilepsy were based on use in patients with partial seizures 12 years of age and older, most of whom were taking enzyme-inducing …”
Check it at the source: the phenobarbital FDA label on DailyMed (effective August 27, 2026); the tiagabine FDA label on DailyMed (effective September 30, 2021, Teva Pharmaceuticals USA, Inc.).
What does the phenobarbital label say about tiagabine?
Phenobarbital's label does not name tiagabine itself; it warns about its class (Anti-seizure medicines):
Phenobarbital label, warnings and precautionsIf a rash occurs, the patient should be evaluated for signs and symptoms of Drug Reaction with Eosinophilia and Systemic Symptoms [see Warnings and Precautions (5.6)]. Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), also known as multiorgan hypersensitivity, has been reported in patients taking antiepileptic drugs, including phenobarbital.
Phenobarbital label, warnings and precautionsAntiepileptic drugs (AEDs) increase the risk of suicidal thoughts or behavior in adolescents and adults.
Source: FDA drug label (Phenobarbital), Chartwell RX, LLC, effective August 27, 2026 (SPL set 74428144-fb24-40a5-a670-3b876e2d116c), via openFDA; the full label on DailyMed
What does the tiagabine label say about phenobarbital?
Tiagabine label, drug interactionsCarbamazepine, phenytoin, primidone, and phenobarbital are generally classified as enzyme inducers; valproate and gabapentin are not.
Tiagabine label, warningsThe tiagabine HCl dosing recommendations in current labeling for treatment of epilepsy were based on use in patients with partial seizures 12 years of age and older, most of whom were taking enzyme-inducing antiepileptic drugs (AEDs; e.g., carbamazepine, phenytoin, primidone and phenobarbital) which lower plasma levels of tiagabine HCl by inducing its metabolism.
Source: FDA drug label (Tiagabine Hydrochloride), NDA020646 (Cephalon), as published by Teva Pharmaceuticals USA, Inc., effective September 30, 2021 (SPL set 953ef3cc-e3cb-480f-b9ea-256520fd62b8), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Phenobarbital | Tiagabine | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.213 per tablet 100 mg tablet | $2.62 per tablet 2 mg tablet |
| Shortage now | A presentation being discontinued | A presentation being discontinued |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once