Estradiol and Levothyroxine and liothyronine interaction
Estradiol and Levothyroxine and liothyronine: both prescribing labels describe an interaction that usually calls for monitoring, a dose change, or spacing the doses.
Usually manageable with monitoring or a dose change. Tell your pharmacist you take both.
What the FDA labels say
From the Estradiol (Delestrogen) label · effective 2026-05-13
Hypothyroidism Estrogen administration leads to increased thyroid-binding globulin (TBG) levels.
Patients with normal thyroid function can compensate for the increased TBG by making more thyroid hormone, thus maintaining free T 4 and T 3 serum concentrations in the normal range.
Patients dependent on thyroid hormone replacement therapy who are also receiving estrogens may require increased doses of their thyroid replacement therapy.
These patients should have their thyroid function monitored in order to maintain their free thyroid hormone levels in an acceptable range.
Increased thyroid-binding globulin (TBG) levels leading to increased circulating total thyroid hormone levels as measured by protein-bound iodine (PBI), T 4 levels (by column or by radioimmunoassay) or T 3 levels by radioimmunoassay.
From the Levothyroxine and liothyronine (NP Thyroid 60) label · effective 2026-01-01
Estrogen, Oral Contraceptives — Estrogens tend to increase serum thyroxine-binding globulin (TBg).
In a patient with a nonfunctioning thyroid gland who is receiving thyroid replacement therapy, free levothyroxine may be decreased when estrogens are started thus increasing thyroid requirements.
Therefore, patients without a functioning thyroid gland who are on thyroid replacement therapy may need to increase their thyroid dose if estrogens or estrogen-containing oral contraceptives are given.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.