Estradiol and norethindrone and Levothyroxine interaction
Estradiol and norethindrone and Levothyroxine: 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 and norethindrone (Estradiol / Norethindrone Acetate) label · effective 2026-06-26
Discontinue estrogen if severe hypercalcemia, loss of vision, severe hypertriglyceridemia or cholestatic jaundice occurs ( 5.5 , 5.6 , 5.9 , 5.10 ) Monitor thyroid function in women on thyroid replacement therapy ( 5.11 , 5.18 )
Exacerbation of Hypothyroidism Estrogen administration leads to increased thyroid-binding globulin (TBG) levels.
Women 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.
Women dependent on thyroid hormone replacement therapy who are also receiving estrogen may require increased doses of their thyroid replacement therapy.
Monitor thyroid function in these women during treatment with Estradiol/Norethindrone Acetate Tablets to maintain their free thyroid hormone levels in an acceptable range.
From the Levothyroxine (Levothyroxine Sodium) label · effective 2024-07-10
…1: Drugs That May Alter T 4 and Triiodothyronine (T 3 ) Serum Transport Without Effecting Free Thyroxine (FT 4 ) 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.
Pregnancy, infectious hepatitis, estrogens, estrogen containing oral contraceptives, and acute intermittent porphyria increase TBG concentrations.
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.