What the FDA labels say about taking them together
Buprenorphine and phenytoin
Buprenorphine's FDA label of June 5, 2026 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name buprenorphine. The buprenorphine label: “The effects of co-administered CYP3A4 inducers on buprenorphine exposure in patients treated with BRIXADI have not been studied. Buprenorphine is metabolized to norbuprenorphine primarily by CYP3A4; …”
Check it at the source: the buprenorphine FDA label on DailyMed (effective June 5, 2026); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the buprenorphine label say about phenytoin?
Buprenorphine label, drug interactionsCYP3A4 Inducers Clinical Impact: The concomitant use of buprenorphine and CYP3A4 inducers can decrease the plasma concentration of buprenorphine, potentially resulting in decreased efficacy or onset of a withdrawal syndrome in patients who have developed physical dependence to buprenorphine. … tablets dosage reduction and monitor for signs of respiratory depression. Examples: Rifampin, carbamazepine, phenytoin
Brixadi label (Braeburn Inc., December 31, 2025), drug interactionsClinical Impact: The effects of co-administered CYP3A4 inducers on buprenorphine exposure in patients treated with BRIXADI have not been studied. Buprenorphine is metabolized to norbuprenorphine primarily by CYP3A4; therefore, potential interactions may occur when BRIXADI is given concurrently with agents that affect CYP3A4 activity. … that permits more precise dose adjustments [see Clinical Pharmacology (12.3) ]. Rifampin, carbamazepine, phenytoin, phenobarbital Antiretrovirals: Non-nucleoside reverse transcriptase inhibitors (NNRTIs)
Source: FDA drug label (Brixadi, NDA210136), Braeburn Inc., effective December 31, 2025 (SPL set 5d8a8fd0-8619-422a-a664-d1d2e8970f48), via openFDA
Source: FDA drug label (Butrans, NDA021306), Knoa Pharma LLC, effective May 1, 2026 (SPL set 794aa355-66de-41b8-aedf-f2c40f6bc664), via openFDA
Source: FDA drug label (Sublocade, NDA209819), Indivior Inc., effective July 27, 2026 (SPL set 6189fb21-9432-45f8-8481-0bfaf3ccde95), via openFDA
Source: FDA drug label (Buprenorphine HCl), SpecGx LLC, effective June 5, 2026 (SPL set b60d514d-a88a-4fa2-a5b0-30ac29e04973), via openFDA; the full label on DailyMed
What does the phenytoin label say about buprenorphine?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name buprenorphine 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
| Buprenorphine | Phenytoin | |
|---|---|---|
| Labeled for | Opioid use disorder, Pain | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.277 per tablet 2 mg tablet sl | $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