What the FDA labels say about taking them together
Caffeine and phenytoin
Caffeine's FDA label of July 29, 2026 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name caffeine. The caffeine label: “Based on adult data, lower doses of caffeine may be needed following coadministration of drugs which are reported to decrease caffeine elimination and higher caffeine doses may be needed following coadministration of …”
Check it at the source: the caffeine FDA label on DailyMed (effective July 29, 2026, Sagent Pharmaceuticals); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the caffeine label say about phenytoin?
Caffeine label, drug interactionsBased on adult data, lower doses of caffeine may be needed following coadministration of drugs which are reported to decrease caffeine elimination (e.g., cimetidine and ketoconazole) and higher caffeine doses may be needed following coadministration of drugs that increase caffeine elimination (e.g., phenobarbital and phenytoin).
Source: FDA drug label (caffeine citrate), Sagent Pharmaceuticals, effective July 29, 2026 (SPL set 5f38c395-0093-4afd-89ec-f96e5dc0934a), via openFDA; the full label on DailyMed
What does the phenytoin label say about caffeine?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name caffeine 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
| Caffeine | Phenytoin | |
|---|---|---|
| Labeled for | n/a | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.083 per tablet 200 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