What the FDA labels say about taking them together
Estradiol and phenobarbital
Estradiol's FDA label of April 3, 2024 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name estradiol. The estradiol label: “Inducers of CYP3A4, such as St. John’s wort ( Hypericum perforatum ) preparations, phenobarbital, carbamazepine and rifampin, may reduce plasma concentrations of estrogens, possibly resulting in a decrease in …”
Check it at the source: the estradiol FDA label on DailyMed (effective April 3, 2024, Amneal Pharmaceuticals LLC); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the estradiol label say about phenobarbital?
Estradiol label, drug interactionsInducers of CYP3A4, such as St. John’s wort ( Hypericum perforatum ) preparations, phenobarbital, carbamazepine and rifampin, may reduce plasma concentrations of estrogens, possibly resulting in a decrease in therapeutic effects and/or changes in the uterine bleeding profile.
Source: FDA drug label (YUVAFEM), Amneal Pharmaceuticals LLC, effective April 3, 2024 (SPL set 30c7f6ba-7a9e-4853-b3e4-e00a46560224), via openFDA; the full label on DailyMed
What does the phenobarbital label say about estradiol?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name estradiol 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
| Estradiol | Phenobarbital | |
|---|---|---|
| Labeled for | Menopause symptoms, Breast cancer, Osteoporosis | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.0635 per tablet 1 mg tablet | $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