What the FDA labels say about taking them together
Liothyronine and phenobarbital
Liothyronine's FDA label of June 4, 2026 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name liothyronine. The liothyronine label: “Drug or Drug Class Effect Phenobarbital Rifampin Phenobarbital has been shown to reduce the response to thyroxine.”
Check it at the source: the liothyronine FDA label on DailyMed (effective June 4, 2026, Mylan Pharmaceuticals Inc.); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the liothyronine label say about phenobarbital?
Liothyronine label, drug interactionsDrug or Drug Class Effect Phenobarbital Rifampin Phenobarbital has been shown to reduce the response to thyroxine.
Source: FDA drug label (Liothyronine Sodium), NDA010379 (King Pharms), as published by Mylan Pharmaceuticals Inc., effective June 4, 2026 (SPL set 115a84c2-0126-4dd7-816e-1873875f1e49), via openFDA; the full label on DailyMed
What does the phenobarbital label say about liothyronine?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name liothyronine 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
| Liothyronine | Phenobarbital | |
|---|---|---|
| Labeled for | Hypothyroidism | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.294 per tablet 25 mcg 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