What the FDA labels say about taking them together
Folic acid and phenytoin
Folic acid's FDA label of July 24, 2026 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name folic acid. The folic acid label: “A patient whose epilepsy is completely controlled by phenytoin may require increased doses to prevent convulsions if folic acid is given.”
Check it at the source: the folic acid FDA label on DailyMed (effective July 24, 2026, Rising Pharma Holdings, Inc.); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the folic acid label say about phenytoin?
Folic acid label, drug interactionsA patient whose epilepsy is completely controlled by phenytoin may require increased doses to prevent convulsions if folic acid is given.
Folic Acid label (Ayurax, LLC, February 11, 2026), drug interactionsDRUG INTERACTIONS Anticonvulsant action of phenytoin is antagonized by folic acid. ( 7 ) Multiple drug classes, including anticonvulsants, antibiotic/antimicrobial agents, folate antagonists, GI-binding agents, and oral contraceptives, may reduce folic acid absorption or folate levels.
Source: FDA drug label (Folic Acid, NDA216395), Ayurax, LLC, effective February 11, 2026 (SPL set 96618bf8-6c03-4df3-9896-b7ef27ca392a), via openFDA
Source: FDA drug label (Folic Acid), Rising Pharma Holdings, Inc., effective July 24, 2026 (SPL set 0baa10dd-6d1d-4946-8236-566451132da3), via openFDA; the full label on DailyMed
What does the phenytoin label say about folic acid?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name folic acid in these sections. A label lists what its studies and reports found; it is not a complete list.
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
| Folic acid | Phenytoin | |
|---|---|---|
| Labeled for | n/a | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.0201 per tablet 1 mg tablet | $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