What the FDA labels say about taking them together
Buprenorphine and phenobarbital
Buprenorphine's FDA label (Brixadi) of December 31, 2025 names phenobarbital in its drug interactions section; the phenobarbital 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 phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the buprenorphine label say about phenobarbital?
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. … 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 (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 phenobarbital label say about buprenorphine?
Phenobarbital's label (effective August 27, 2026) 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 (Phenobarbital), Chartwell RX, LLC, effective August 27, 2026 (SPL set 74428144-fb24-40a5-a670-3b876e2d116c), 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 | Phenobarbital | |
|---|---|---|
| Labeled for | Opioid use disorder, Pain | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.277 per tablet 2 mg tablet sl | $0.213 per tablet 100 mg tablet |
| Shortage now | No current entry | A presentation being discontinued |
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