Lanthanum and Levothyroxine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Lanthanum
Levothyroxine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Reduced levothyroxine exposure and serum thyroxine (T4) level, reduced efficacy of levothyroxine and an increased risk of hypothyroidism
Interaction Deep Dive
Concurrent use of lanthanum carbonate and levothyroxine results in decreased absorption of levothyroxine. In a study, concurrent administration of lanthanum carbonate with levothyroxine significantly reduced the exposure of levothyroxine by about 40%1. Avoid concomitant use if possible. If coadministration is required, maximally separate administration 2 and administer levothyroxine at least 4 hours apart from lanthanum carbonate 345. Monitor for an adequate response to levothyroxine therapy (T4 and TSH levels) and adjust the levothyroxine dose appropriately 1.
Why it happens (mechanism)
Reduced absorption of levothyroxine by binding with lanthanum carbonate
Literature reports
1 report — tap to read
a) There was a reduction in the exposure of levothyroxine when concomitantly administered with lanthanum carbonate according to a study of 6 euthyroid healthy volunteers. Patients 27 to 40 years with normal serum thyroxine (T4) and TSH levels at baseline were administered levothyroxine sodium 1 mg orally at visit 1, followed by levothyroxine plus colesevelam 3.75 g or lanthanum carbonate 500 mg at 2 subsequent study visits at least 3 weeks apart. The mean increase of T4 AUC when levothyroxine was given alone was 1692 +/-183.5 mcg x min/dL, but the increase was blunted when concomitant lanthanum carbonate was administered (982.5 +/- 172.3 mcg x min/dL; 59.1% of the area of levothyroxine alone) 1.
Common questions
Can I take Lanthanum and Levothyroxine together?
Reduced levothyroxine exposure and serum thyroxine (T4) level, reduced efficacy of levothyroxine and an increased risk of hypothyroidism Always confirm with your pharmacist or prescriber before making any change.
How serious is the Lanthanum and Levothyroxine interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Lanthanum or Levothyroxine need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (5)
- Weitzman SP, Ginsburg KC, & Carlson HE: Colesevelam hydrochloride and lanthanum carbonate interfere with the absorption of levothyroxine. Thyroid 2009; 19(1):77-79. PubMed
- Centanni M, Duntas L, Feldt-Rasmussen U, et al: ETA guidelines for the use of levothyroxine sodium preparations in monotherapy to optimize the treatment of hypothyroidism. Eur Thyroid J 2025; 14(4):e250123. DOI
- Product Information: SYNTHROID(R) oral tablets, levothyroxine sodium oral tablets. AbbVie Inc (per FDA), North Chicago, IL, 2024. DailyMed
- Product Information: TIROSINT(R)-SOL oral solution, levothyroxine sodium oral solution. IBSA Pharma Inc. (per FDA), Parsippany, NJ, 2023. DailyMed
- Product Information: LEVO-T® oral tablets, levothyroxine sodium oral tablets. Neolpharma Inc, Caguas, PR, 2026. DailyMed
Keep reading about Lanthanum
Keep reading about Levothyroxine
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