What the FDA labels say about taking them together
Levothyroxine and liothyronine
Liothyronine's FDA label of June 4, 2026 names levothyroxine in its drug interactions section; the levothyroxine labels PlainMeds reads (4) do not name liothyronine. The liothyronine label: “Other drugs: Amiodarone; Amiodarone inhibits peripheral conversion of levothyroxine (T4) to triiodothyronine (T3) and may cause isolated biochemical changes in clinically euthyroid patients.”
Check it at the source: the levothyroxine FDA label on DailyMed (effective February 20, 2024, AbbVie Inc.); the liothyronine FDA label on DailyMed (effective June 4, 2026, Mylan Pharmaceuticals Inc.).
What does the levothyroxine label say about liothyronine?
Levothyroxine's label (effective February 20, 2024) and its 3 other brand-application labels 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 (Synthroid), AbbVie Inc., effective February 20, 2024 (SPL set 1e11ad30-1041-4520-10b0-8f9d30d30fcc), via openFDA; the full label on DailyMed
What does the liothyronine label say about levothyroxine?
Liothyronine label, drug interactionsOther drugs: Amiodarone; Amiodarone inhibits peripheral conversion of levothyroxine (T4) to triiodothyronine (T3) and may cause isolated biochemical changes (increase in serum free-T4, and decreased or normal free-T3) in clinically euthyroid patients.
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
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
| Levothyroxine | Liothyronine | |
|---|---|---|
| Labeled for | Hypothyroidism | Hypothyroidism |
| Boxed warning | Yes | Yes |
| Pharmacy cost (NADAC) | $0.0588 per tablet 112 mcg tablet | $0.294 per tablet 25 mcg tablet |
| Shortage now | No current entry | No current entry |
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