Levothyroxine and Tibolone: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Levothyroxine
Tibolone
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Reduced serum-free thyroxine exposure
Interaction Deep Dive
Estrogens, including those in oral combined hormonal contraceptives and in hormone-replacement therapy, may raise serum concentrations of thyroxine-binding globulin, necessitating an increase in the dose of replacement thyroid hormone therapy312. Monitor thyroid-stimulating hormone (TSH) level 4.
Why it happens (mechanism)
Estrogen-induced increase in serum thyroxine-binding globulin concentration
Literature reports
1 report — tap to read
a) Women with hypothyroidism who are treated with thyroxine, who then receive estrogen, may experience a decrease in the concentration of serum-free thyroxine, thereby increasing serum thyrotropin concentrations and increasing the need for thyroxine. Thirty-six women were evaluated for the effects of estrogen administration on pituitary-thyroid function. Twenty-five of these women were receiving thyroxine therapy for chronic hypothyroidism, 18 of these patients received thyroid replacement therapy and 7 received thyroxine for thyrotropin suppression for thyroid cancer. In women with normal thyroid function, serum-free thyroxine and thyrotropin concentrations did not change. The mean serum thyroxine concentration increased 30% and serum thyroxine-binding globulin level increased 54%. In women with hypothyroidism, the serum-free thyroxine concentration decreased 18% and the serum thyrotropin concentration increased 256%. Thyrotropin levels increased to greater than 7 mcU/mL in seven women receiving thyroid replacement therapy and to greater than 1mcU/mL in three women in the thyrotropin-suppression group, necessitating increases in thyroxine doses 5.
Common questions
Can I take Levothyroxine and Tibolone together?
Reduced serum-free thyroxine exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Levothyroxine and Tibolone interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Levothyroxine or Tibolone need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (5)
- Product Information: SYNTHROID(R) oral tablets, levothyroxine sodium oral tablets. AbbVie Inc. (per FDA), North Chicago, IL, 2017. DailyMed
- Product Information: levothyroxine sodium intravenous injection, intramuscular injection, levothyroxine sodium intravenous injection, intramuscular injection. Fresenius Kabi Canada Ltd. (per Health Canada), Toronto, ON, Canada, 2017. DailyMed
- Product Information: ANNOVERA(TM) vaginal system, segesterone acetate ethinyl estradiol vaginal system. Population Council (per FDA), New York, NY, 2018.
- Product Information: ALESSE(R) 28 oral tablets, levonorgestrel ethinyl estradiol oral tablets. Cadence Health (per FDA), New York, NY, 2024.
- Arafah B: Increased need for thyroxine in women with hypothyroidism during estrogen therapy. N Engl J Med 2001; 344(23):1743-1748. PubMed
Keep reading about Levothyroxine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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