What the FDA labels say about taking them together
Phenobarbital and sirolimus
Sirolimus's FDA label of January 28, 2026 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name sirolimus. The sirolimus label: “Drugs and other agents that could decrease sirolimus concentrations: Carbamazepine, phenobarbital, phenytoin, rifapentine, St. John’s Wort ( Hypericum perforatum )”
Check it at the source: the phenobarbital FDA label on DailyMed (effective August 27, 2026); the sirolimus FDA label on DailyMed (effective January 28, 2026, Glenmark Pharmaceuticals Inc., USA).
What does the phenobarbital label say about sirolimus?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name sirolimus 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
What does the sirolimus label say about phenobarbital?
Sirolimus label, drug interactionsDrugs and other agents that could decrease sirolimus concentrations: Carbamazepine, phenobarbital, phenytoin, rifapentine, St. John’s Wort ( Hypericum perforatum )
Source: FDA drug label (sirolimus), Glenmark Pharmaceuticals Inc., USA, effective January 28, 2026 (SPL set 57fb4d90-3ccb-4a69-af1e-53be83f7a504), 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
| Phenobarbital | Sirolimus | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Organ transplant rejection |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.213 per tablet 100 mg tablet | $0.723 per tablet 1 mg tablet |
| Shortage now | A presentation being discontinued | 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