Ferrous Sulfate and Levothyroxine Interaction
Drug interaction information between Ferrous Sulfate and Levothyroxine.
Ferrous Sulfate and Levothyroxine have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Ferrous Sulfate and Levothyroxine. Major interactions are generally avoided, moderate ones may need monitoring or a dose adjustment, and minor ones are usually low-risk. This page shows the documented mechanism and guidance. Label-documented interactions are not a complete safety review, so always confirm your own medications with a pharmacist or doctor. Educational information, not medical advice.
How They Interact
Ferrous sulfate can stick to levothyroxine in your stomach, which prevents your body from absorbing the thyroid medicine correctly.
What To Do
Take these two medications at least four hours apart to make sure your thyroid medicine works as it should.
FDA Label Information
Drug or Drug Class Effect Phosphate Binders (e.g., calcium carbonate, ferrous sulfate, sevelamer, lanthanum) Phosphate binders may bind to levothyroxine. Drug or Drug Class Effect Phosphate Binders (e.g., calcium carbonate, ferrous sulfate, sevelamer, lanthanum) Phosphate binders may bind to levothyroxine.
Levothyroxine Also Interacts With
- Sertraline minor
- Furosemide minor
- Propranolol minor
- Amitriptyline minor
- Carbamazepine minor
Frequently Asked Questions
Can I take Ferrous Sulfate and Levothyroxine together?
This is a minor interaction. Take these two medications at least four hours apart to make sure your thyroid medicine works as it should.
How serious is the interaction between Ferrous Sulfate and Levothyroxine?
This interaction is classified as "minor" severity by the FDA. Minor interactions are unlikely to cause significant problems but should still be mentioned to your healthcare provider.
Why do Ferrous Sulfate and Levothyroxine interact?
Ferrous sulfate can stick to levothyroxine in your stomach, which prevents your body from absorbing the thyroid medicine correctly.
Understanding the Ferrous Sulfate and Levothyroxine Interaction
FDA-approved prescribing information for these two drugs flags their combination as a minor-severity interaction. Ferrous Sulfate belongs to the Iron Supplement class and Levothyroxine belongs to the Thyroid Hormone class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: Ferrous sulfate can stick to levothyroxine in your stomach, which prevents your body from absorbing the thyroid medicine correctly. Severity tiers matter: major flags generally advise avoidance, moderate flags often require monitoring or dose adjustment, and minor flags may only call for awareness.
Context around a specific patient determines real-world impact. Ferrous Sulfate has 2 total documented interactions on file in this dataset, and Levothyroxine has 22. Each additional medication compounds the interaction surface, which is why pharmacists run full-profile checks rather than evaluating one pair at a time. FDA-derived guidance for this pair is: Take these two medications at least four hours apart to make sure your thyroid medicine works as it should. Timing of doses, renal and hepatic function, age, and other concurrent prescriptions all shape whether a labeled interaction matters clinically.
An interaction flag is not a verdict. A large share of labeled interactions are managed routinely in clinical practice, the fix may be as simple as spacing doses or adding a monitoring test. Others require the prescriber to choose a different medication entirely. This page surfaces FDA-sourced labeling and openFDA data for educational purposes only; it is not medical advice and cannot account for your full clinical picture. Never start, stop, or adjust either Ferrous Sulfate or Levothyroxine based on a web page, speak with your prescriber or pharmacist before making any change.
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. Always consult your healthcare provider about drug interactions.
Read our methodology - how this data is sourced, computed, and verified.