What the FDA labels say about taking them together
Gabapentin and phenytoin
Gabapentin's FDA label of May 12, 2026 names phenytoin in its drug interactions section; phenytoin's label does not name gabapentin itself but warns about its class (Anti-seizure medicines). The gabapentin label: “Phenytoin In a single (400 mg) and multiple dose (400 mg three times a day) study of NEURONTIN in epileptic patients (N=8) maintained on phenytoin monotherapy for at least 2 months, gabapentin had no effect on the …”
Check it at the source: the gabapentin FDA label on DailyMed (effective May 12, 2026, Viatris Specialty LLC); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the gabapentin label say about phenytoin?
Gabapentin label, drug interactionsPhenytoin In a single (400 mg) and multiple dose (400 mg three times a day) study of NEURONTIN in epileptic patients (N=8) maintained on phenytoin monotherapy for at least 2 months, gabapentin had no effect on the steady-state trough plasma concentrations of phenytoin and phenytoin had no effect on gabapentin pharmacokinetics.
Source: FDA drug label (Gralise, NDA022544), Almatica Pharma LLC, effective June 30, 2026 (SPL set 466273b1-c9fc-3930-c94b-aa11394d5140), via openFDA
Source: FDA drug label (Gabapentin, NDA021129), Mylan Pharmaceuticals Inc., effective April 12, 2025 (SPL set cff7de45-148b-4e96-88fd-6052bf75b5f7), via openFDA
Source: FDA drug label (Neurontin), Viatris Specialty LLC, effective May 12, 2026 (SPL set 97935fd9-1d4a-43b6-a5d9-de994591187b), via openFDA; the full label on DailyMed
What does the phenytoin label say about gabapentin?
Phenytoin's label does not name gabapentin itself; it warns about its class (Anti-seizure medicines):
Phenytoin label, drug interactionsDrugs That Affect Phenytoin Concentrations Interacting Agent Examples Drugs that may increase phenytoin serum levels Antiepileptic drugs Ethosuximide, felbamate, oxcarbazepine, methsuximide, topiramate Azoles Fluconazole, ketoconazole, itraconazole, miconazole, voriconazole Antineoplastic agents Capecitabine, fluorouracil Antidepressants Fluoxetine, fluvoxamine, sertraline Gastric acid reducing agents H 2 antagonists (cimetidine), omeprazole Sulfonamides Sulfamethizole, sulfaphenazole, sulfadiazine …
Phenytoin label, drug interactionsPhenytoin and antacids should not be taken at the same time of day Antineoplastic agents usually in combination Bleomycin, carboplatin, cisplatin, doxorubicin, methotrexate Antiviral agents Fosamprenavir, nelfinavir, ritonavir Antiepileptic drugs Carbamazepine, vigabatrin Other Chronic alcohol abuse, diazepam, diazoxide, folic acid, reserpine, rifampin, St. John’s wort The induction potency of St. John’s wort may vary widely based on preparation. …
Source: FDA drug label (Phenytek), Mylan Pharmaceuticals Inc., effective October 15, 2024 (SPL set 0f94c791-8b07-4b41-927e-c9f28bec5f60), 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
| Gabapentin | Phenytoin | |
|---|---|---|
| Labeled for | Nerve pain and fibromyalgia, Seizures and epilepsy | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.0218 per capsule 100 mg capsule | $0.145 per capsule 100 mg capsule |
| Shortage now | No current entry | No current entry |
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