What the FDA labels say about taking them together
Carbamazepine and phenobarbital
Carbamazepine's FDA label of August 20, 2026 names phenobarbital in its drug interactions section, and phenobarbital's label names carbamazepine too. The carbamazepine label: “Aminophylline, cisplatin, doxorubicin HCL, felbamate, fosphenytoin, methsuximide, phenobarbital, phenytoin, primidone, rifampin and theophylline. …”
Check it at the source: the carbamazepine FDA label on DailyMed (effective August 20, 2026, Novartis Pharmaceuticals Corporation); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the carbamazepine label say about phenobarbital?
Carbamazepine label, drug interactionsDrugs that have been shown, or that would be expected, to decrease plasma carbamazepine levels include cisplatin, doxorubicin HCl, felbamate, fosphenytoin, rifampin, phenobarbital, phenytoin, primidone, methsuximide, theophylline, aminophylline.
Carbamazepine label, warningsHypersensitivity Hypersensitivity reactions to carbamazepine have been reported in patients who previously experienced this reaction to anticonvulsants, including phenytoin, primidone, and phenobarbital.
Carbatrol label (Takeda Pharmaceuticals America, Inc., August 17, 2026), drug interactionsAminophylline, cisplatin, doxorubicin HCL, felbamate, fosphenytoin, methsuximide, phenobarbital, phenytoin (1), primidone, rifampin and theophylline. (1) Phenytoin plasma levels have also been reported to increase and decrease in the presence of carbamazepine, see below.
Equetro label (Validus Pharmaceuticals LLC, August 19, 2025), drug interactionsSuch drugs include the following: Aminophylline, c isplatin, doxorubicin, felbamate, phosphenytoin, methsuximide, phenobarbital, phenytoin, primidone, rifampin and theophylline.
Source: FDA drug label (Carbatrol, NDA020712), Takeda Pharmaceuticals America, Inc., effective August 17, 2026 (SPL set bc03e499-5bac-4293-bff4-6864153a624d), via openFDA
Source: FDA drug label (Equetro, NDA021710), Validus Pharmaceuticals LLC, effective August 19, 2025 (SPL set be478f3c-40f6-47cc-8ab9-f420a9372b1c), via openFDA
Source: FDA drug label (Tegretol), Novartis Pharmaceuticals Corporation, effective August 20, 2026 (SPL set 8d409411-aa9f-4f3a-a52c-fbcb0c3ec053), via openFDA; the full label on DailyMed
What does the phenobarbital label say about carbamazepine?
Sezaby label (Sun Pharmaceutical Industries, Inc., December 23, 2025), warnings and precautionsAdditionally, consider alternatives to structurally similar drugs such as carboxamides (e.g., carbamazepine) and hydantoins (e.g., phenytoin) in these same patients.
Source: FDA drug label (Sezaby, NDA215910), Sun Pharmaceutical Industries, Inc., effective December 23, 2025 (SPL set 8c7d0402-4977-4c25-bc4b-11db91339e9a), via openFDA
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
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
| Carbamazepine | Phenobarbital | |
|---|---|---|
| Labeled for | Bipolar disorder, Seizures and epilepsy | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.119 per tablet 200 mg tablet | $0.213 per tablet 100 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