What the FDA labels say about taking them together
Calcifediol and phenobarbital
Calcifediol's FDA label of January 19, 2024 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name calcifediol. The calcifediol label: “The half-life of calcifediol is reduced by drugs stimulating microsomal hydroxylation, such as phenobarbital or other anticonvulsants.”
Check it at the source: the calcifediol FDA label on DailyMed (effective January 19, 2024, OPKO Pharmaceuticals LLC); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the calcifediol label say about phenobarbital?
Calcifediol label, drug interactionsThe half-life of calcifediol is reduced by drugs stimulating microsomal hydroxylation, such as phenobarbital or other anticonvulsants.
Source: FDA drug label (Rayaldee), NDA208010 (Eirgen), as published by OPKO Pharmaceuticals LLC, effective January 19, 2024 (SPL set 6a95effd-32a5-46b6-a30e-7f4f9bf8cc77), via openFDA; the full label on DailyMed
What does the phenobarbital label say about calcifediol?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name calcifediol 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
| Calcifediol | Phenobarbital | |
|---|---|---|
| Labeled for | n/a | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $41.26 per capsule 30 mcg capsule (hard) | $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