Levothyroxine and Mifepristone: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Mifepristone
Levothyroxine
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
Decreased levothyroxine efficacy
Interaction Deep Dive
Coadministration of levothyroxine and mifepristone may result in decreased free thyroxine (FT4) levels, and increased levothyroxine doses may be necessary3. If concomitant use is required, consider increasing levothyroxine dose 1. Monitor closely and adjust levothyroxine dose if necessary 2.
Why it happens (mechanism)
Reduced absorption of levothyroxine
Literature reports
1 report — tap to read
a) Decreased free thyroxine (FT4) levels with coadministration of levothyroxine and mifepristone was described in a retrospective, longitudinal case series. Five female patients with Cushing disease and central hypothyroidism with increased levothyroxine requirements during treatment with mifepristone were followed for a median duration of 16 months (IQR, 8.25 to 36 months). Patients were a median age of 50 years (interquartile range [IQR], 47 to 64.5 years) and had a median increase in levothyroxine requirement of 83.3% (IQR, 71% to 350%) during coadministration with mifepristone. Four of the patients had a decrease in body weight, with a median decrease of 4.7% (IQR, 0.2% to 26.1%). Medication adherence was confirmed and clinical malabsorption was excluded for each patient. Patients denied the addition of any new medications that could interfere with levothyroxine absorption during coadministration of mifepristone. Suspected mechanisms for the decrease in FT4 levels include intestinal malabsorption, decreased residual thyroid function, and increased inactivation of T4 via deiodinases 3.
Common questions
Can I take Levothyroxine and Mifepristone together?
Decreased levothyroxine efficacy Always confirm with your pharmacist or prescriber before making any change.
How serious is the Levothyroxine and Mifepristone 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 Mifepristone 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 (3)
- Centanni M, Duntas L, Feldt-Rasmussen U, et al: ETA guidelines for the use of levothyroxine sodium preparations in monotherapy to optimize the treatment of hypothyroidism. Eur Thyroid J 2025; 14(4):e250123. PubMed
- Liu H, Lu M, Hu J, et al: Medications and food interfering with the bioavailability of levothyroxine: a systematic review. Ther Clin Risk Manag 2023; 19:503-523. DOI
- Guarda FJ, Findling J, Yuen KCJ, et al: Mifepristone increases thyroid hormone requirements in patients with central hypothyroidism: a multicenter study. J Endocr Soc 2019; 3(9):1707-1714. PubMed
Keep reading about Mifepristone
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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