What the FDA labels say about taking them together
Estrogens conjugated and phenobarbital
Estrogens conjugated's FDA label of June 4, 2026 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name estrogens conjugated. The estrogens conjugated 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 estrogens conjugated FDA label on DailyMed (effective June 4, 2026, Wyeth Pharmaceuticals LLC, a subsidiary of Pfizer Inc.); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the estrogens conjugated label say about phenobarbital?
Estrogens conjugated 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 (Premarin), Wyeth Pharmaceuticals LLC, a subsidiary of Pfizer Inc., effective June 4, 2026 (SPL set 258e1602-a3cf-4ccc-ca80-73dbbfb812ff), via openFDA; the full label on DailyMed
What does the phenobarbital label say about estrogens conjugated?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name estrogens conjugated 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
| Estrogens conjugated | Phenobarbital | |
|---|---|---|
| Labeled for | Menopause symptoms, Breast cancer, Osteoporosis | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $5.47 per tablet 0.625 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