What the FDA labels say about taking them together
Lanthanum and levothyroxine
Lanthanum's FDA label of December 31, 2024 names levothyroxine in its drug interactions section, and levothyroxine's label names lanthanum too. The lanthanum label: “The bioavailability of levothyroxine was decreased by approximately 40% when taken together with FOSRENOL.”
Check it at the source: the lanthanum FDA label on DailyMed (effective December 31, 2024, Takeda Pharmaceuticals America, Inc.); the levothyroxine FDA label on DailyMed (effective February 20, 2024, AbbVie Inc.).
What does the lanthanum label say about levothyroxine?
Lanthanum label, drug interactionsThe bioavailability of levothyroxine was decreased by approximately 40% when taken together with FOSRENOL.
Source: FDA drug label (Fosrenol), Takeda Pharmaceuticals America, Inc., effective December 31, 2024 (SPL set f10776b2-2c25-4343-aabe-68f302e5cb54), via openFDA; the full label on DailyMed
What does the levothyroxine label say about lanthanum?
Levothyroxine label, drug interactionsDrug or Drug Class Effect Phosphate Binders (e.g., calcium carbonate, ferrous sulfate, sevelamer, lanthanum) Phosphate binders may bind to levothyroxine.
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
| Lanthanum | Levothyroxine | |
|---|---|---|
| Labeled for | n/a | Hypothyroidism |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $3.15 per tablet 1,000 mg tablet chw | $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