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. This page displays the available source-record category and label text. The category is not an individual risk estimate or medication-combination direction.
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.
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
What SPL severity band is on file for Levothyroxine + Furosemide?
Compiled FDA labeling labels this pair minor. That is a source-record field, not an individual medication-combination decision.
Which drug in this pair has the larger labeled-interaction portfolio?
Furosemide has 36 labeled pairs on file vs Levothyroxine's 22. In the minor band specifically: Levothyroxine has 22 (also Sertraline, Propranolol, Ferrous Sulfate, Amitriptyline); Furosemide has 29 (also Methotrexate, Norepinephrine, Ethacrynic Acid, Indomethacin).
What mechanism field is on file for Levothyroxine and Furosemide?
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.
Furosemide carries more major-labeled pairs than Levothyroxine
SPL source-record counts only. This page's band is minor · classes on file: Levothyroxine (Thyroid Hormone); Furosemide (Loop Diuretic).
Furosemide has 3 major-labeled pairs vs Levothyroxine's 0. This page itself is in the minor band, not the major band.
0 major · 0 moderate · 22 minor · 22 total
- Other minor peers for Levothyroxine
- Sertraline
- Propranolol
- Ferrous Sulfate
- Amitriptyline
3 major · 4 moderate · 29 minor · 36 total
- Other minor peers for Furosemide
- Methotrexate
- Norepinephrine
- Ethacrynic Acid
- Indomethacin
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. This registry does not provide individual medication-combination directions.
Read our methodology - how this data is sourced, computed, and verified.