Tamoxifen and Levothyroxine Interaction
Drug interaction information between Tamoxifen and Levothyroxine.
Tamoxifen and Levothyroxine have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Tamoxifen and Levothyroxine. 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
Tamoxifen increases the number of proteins that carry thyroid hormone in your blood, which can change your test results.
FDA Label Information
Drugs That May Alter T4 and Triiodothyronine (T3) Serum Transport Without Affecting Free Thyroxine (FT4) Concentration (Euthyroidism) Drug or Drug Class Effect Clofibrate Estrogen-containing oral contraceptives Estrogens (oral) Heroin / Methadone 5-Fluorouracil Mitotane Tamoxifen These drugs may increase serum thyroxine-binding globulin (TBG) concentration. Drugs That May Alter T4 and Triiodothyronine (T3) Serum Transport Without Affecting Free Thyroxine (FT4) Concentration (Euthyroidism) Drug or Drug Class Effect Clofibrate Estrogen-containing oral contraceptives Estrogens (oral) Heroin /...
Tamoxifen Also Interacts With
- Warfarin major
- Anastrozole major
- Letrozole moderate
- Bupropion minor
- Desvenlafaxine minor
Levothyroxine Also Interacts With
- Sertraline minor
- Furosemide minor
- Propranolol minor
- Ferrous Sulfate minor
- Amitriptyline minor
Frequently Asked Questions
What SPL severity band is on file for Tamoxifen + Levothyroxine?
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?
Levothyroxine has 22 labeled pairs on file vs Tamoxifen's 10. In the minor band specifically: Tamoxifen has 7 (also Bupropion, Desvenlafaxine, Letrozole, Liothyronine); Levothyroxine has 22 (also Sertraline, Furosemide, Propranolol, Ferrous Sulfate).
What mechanism field is on file for Tamoxifen and Levothyroxine?
Tamoxifen increases the number of proteins that carry thyroid hormone in your blood, which can change your test results.
Tamoxifen carries more major-labeled pairs than Levothyroxine
SPL source-record counts only. This page's band is minor · classes on file: Tamoxifen (Selective Estrogen Receptor Modulator (SERM)); Levothyroxine (Thyroid Hormone).
Tamoxifen has 2 major-labeled pairs vs Levothyroxine's 0. This page itself is in the minor band, not the major band.
2 major · 1 moderate · 7 minor · 10 total
- Other minor peers for Tamoxifen
- Bupropion
- Desvenlafaxine
- Letrozole
- Liothyronine
0 major · 0 moderate · 22 minor · 22 total
- Other minor peers for Levothyroxine
- Sertraline
- Furosemide
- Propranolol
- Ferrous Sulfate
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.