Levothyroxine and Furosemide Interaction
Drug interaction information between Levothyroxine and Furosemide.
Levothyroxine and Furosemide have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Levothyroxine and Furosemide. 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
High doses of this water pill can knock thyroid hormones off the proteins they usually travel on in your blood. This changes how much active thyroid hormone is available for your body to use.
What To Do
Your doctor may need to monitor your thyroid levels closely if you are taking high doses of furosemide. They will check to see if your medication dose needs to be changed.
FDA Label Information
Other drugs: Carbamazepine Furosemide (> 80 mg IV) Heparin Hydantoins Non-Steroidal Anti-inflammatory Drugs - Fenamates These drugs may cause protein-binding site displacement. Furosemide has been shown to inhibit the protein binding of T4 to TBG and albumin, causing an increase free T4 fraction in serum. Furosemide competes for T4-binding sites on TBG, prealbumin, and albumin, so that a single high dose can acutely lower the total T4 level.
Levothyroxine Also Interacts With
- Sertraline minor
- Propranolol minor
- Ferrous Sulfate minor
- Amitriptyline minor
- Carbamazepine minor
Furosemide Also Interacts With
- Dutasteride major
- Dutasteride/Tamsulosin major
- Tamsulosin major
- Cyclosporine moderate
- Lithium moderate
Frequently Asked Questions
Can I take Levothyroxine and Furosemide together?
This is a minor interaction. Your doctor may need to monitor your thyroid levels closely if you are taking high doses of furosemide. They will check to see if your medication dose needs to be changed.
How serious is the interaction between Levothyroxine and Furosemide?
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 Levothyroxine and Furosemide interact?
High doses of this water pill can knock thyroid hormones off the proteins they usually travel on in your blood. This changes how much active thyroid hormone is available for your body to use.
Understanding the Levothyroxine and Furosemide Interaction
FDA-approved prescribing information for these two drugs flags their combination as a minor-severity interaction. Levothyroxine belongs to the Thyroid Hormone class and Furosemide belongs to the Loop Diuretic class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: High doses of this water pill can knock thyroid hormones off the proteins they usually travel on in your blood. 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. Levothyroxine has 22 total documented interactions on file in this dataset, and Furosemide has 36. 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: Your doctor may need to monitor your thyroid levels closely if you are taking high doses of furosemide. 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 Levothyroxine or Furosemide 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.