What the FDA labels say about taking them together
Phenytoin and quetiapine
Phenytoin's FDA label of October 15, 2024 names quetiapine in its drug interactions section, and quetiapine's label names phenytoin too. The phenytoin label: “Interacting Agent: Other; Examples: Albendazole, chlorpropamide, clozapine, cyclosporine, digoxin, disopyramide, folic acid, methadone, mexiletine, praziquantel, quetiapine”
Check it at the source: the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.); the quetiapine FDA label on DailyMed (effective April 10, 2026, H2-Pharma, LLC).
What does the phenytoin label say about quetiapine?
Phenytoin label, drug interactionsInteracting Agent: Other; Examples: Albendazole (decreases active metabolite), chlorpropamide, clozapine, cyclosporine, digoxin, disopyramide, folic acid, methadone, mexiletine, praziquantel, quetiapine
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
What does the quetiapine label say about phenytoin?
Quetiapine label, drug interactionsConcomitant use of strong CYP3A4 inducers: Increase quetiapine dose up to 5 fold when used in combination with a chronic treatment (more than 7-14 days) of potent CYP3A4 inducers (e.g., phenytoin, rifampin, St. John’s wort)
Source: FDA drug label (SEROQUEL), NDA020639 (Cheplapharm), as published by H2-Pharma, LLC, effective April 10, 2026 (SPL set 8ae62aaf-f8c5-417f-baac-0098369ca322), 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
| Phenytoin | Quetiapine | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Schizophrenia, Bipolar disorder, Depression |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.145 per capsule 100 mg capsule | $0.127 per tablet 300 mg tablet |
| 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