What the FDA labels say about taking them together
Mifepristone and phenobarbital
Mifepristone's FDA label of September 25, 2025 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name mifepristone. The mifepristone label: “Avoid co-administration of mifepristone and CYP3A inducers such as rifampin, rifabutin, rifapentin, phenobarbital, phenytoin, carbamazepine, and St. John's wort.”
Check it at the source: the mifepristone FDA label on DailyMed (effective September 25, 2025, Corcept Therapeutics Incorporated); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the mifepristone label say about phenobarbital?
Mifepristone label, drug interactionsAvoid co-administration of mifepristone and CYP3A inducers such as rifampin, rifabutin, rifapentin, phenobarbital, phenytoin, carbamazepine, and St. John's wort.
Source: FDA drug label (Mifepristone), Corcept Therapeutics Incorporated, effective September 25, 2025 (SPL set 63c068cd-9370-460f-829b-70e8c7ebe91e), via openFDA; the full label on DailyMed
What does the phenobarbital label say about mifepristone?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name mifepristone 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
| Mifepristone | Phenobarbital | |
|---|---|---|
| Labeled for | n/a | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | n/a | $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