What the FDA labels say about taking them together
Isoproterenol and levothyroxine
Isoproterenol's FDA label of December 16, 2025 names levothyroxine in its drug interactions section; the levothyroxine labels PlainMeds reads (4) do not name isoproterenol.
Check it at the source: the isoproterenol FDA label on DailyMed (effective December 16, 2025, Eugia US LLC); the levothyroxine FDA label on DailyMed (effective February 20, 2024, AbbVie Inc.).
What does the isoproterenol label say about levothyroxine?
Isoproterenol label, drug interactionsClinical Impact; The effects of isoproterenol may be potentiated by tricyclic antidepressants, monoamine oxidase inhibitors, levothyroxine sodium, and certain antihistamines, notablychlorpheniramine, tripelennamine, and diphenhydramine.
Source: FDA drug label (Isoproterenol Hydrochloride), Eugia US LLC, effective December 16, 2025 (SPL set 3e4050e8-7d94-4ed7-951d-1ff818ddadf1), via openFDA; the full label on DailyMed
What does the levothyroxine label say about isoproterenol?
Levothyroxine's label (effective February 20, 2024) and its 3 other brand-application labels do not name isoproterenol 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
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
| Isoproterenol | Levothyroxine | |
|---|---|---|
| Labeled for | n/a | Hypothyroidism |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | n/a | $0.0588 per tablet 112 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