Momelotinib and Levothyroxine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Levothyroxine
Momelotinib
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
Increased risk of hypothyroidism
Interaction Deep Dive
Concomitant use of levothyroxine and tyrosine kinase inhibitors may result in increased risk of hypothyroidism. Closely monitor TSH levels in such patients21. Initiation of imatinib therapy in post-thyroidectomy patients receiving levothyroxine has resulted in elevated levels of thyrotropin (TSH) and symptoms of hypothyroidism. While the exact mechanism for this interaction is unknown, it has been postulated that imatinib, similar to rifAMPin, induces the metabolism of levothyroxine which results in an increase in serum TSH levels. Therefore, when initiating imatinib treatment in hypothyroid, levothyroxine-substituted patients, particular post-thyroidectomy patients, an increase in their levothyroxine dose is advisable. Such patients should be monitored for signs and symptoms of hypothyroidism and the serum thyroxine and TSH levels should be routinely evaluated. A 2-fold increase in the levothyroxine dose before initiating imatinib treatment may be considered 3.
Why it happens (mechanism)
Unknown
Literature reports
1 report — tap to read
a) Symptoms of hypothyroidism developed in post-thyroidectomy patients, on levothyroxine therapy, upon initiation of imatinib therapy. Patients (n=11) with gastrointestinal stromal tumor and medullary thyroid carcinoma were treated with imatinib for 6 months on average. Eight of the patients who underwent total thyroidectomy were also receiving levothyroxine and 3 patients had the thyroid in situ; all patients were euthyroid before treatment with imatinib. Within an average of 2 weeks of commencing imatinib therapy, the thyrotropin levels (TSH) increased to 384%+/-228% of the upper limit. The mean values of free thyroxine (fT4) and free tri-iodothyronine (fT3) decreased to 59% +/- 17% and 63% +/- 4% of the upper limits for fT4 and fT3, respectively, but remained within the reference range. These effects were observed only in post-thyroidectomy patients while patients with a normal functioning thyroid remained euthyroid after commencing imatinib therapy. A stepwise rise in levothyroxine dosage to an average of 206% (range, 100% to 350%) of the dose before imatinib treatment in all post-thyroidectomy patients reversed hypothyroidism only in 3 patients. In the remaining post-thyroidectomy patients, symptoms of hypothyroidism disappeared upon discontinuation of imatinib. Although the exact mechanism of this interaction between imatinib and levothyroxine was not determined, the investigators ruled out other probable causes of hypothyroidism and postulated that induction of levothyroxine metabolism by imatinib may be responsible for the observed hypothyroidism 3.
Common questions
Can I take Momelotinib and Levothyroxine together?
Increased risk of hypothyroidism Always confirm with your pharmacist or prescriber before making any change.
How serious is the Momelotinib and Levothyroxine 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 Momelotinib or Levothyroxine 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)
- Product Information: LEVO-T® oral tablets, levothyroxine sodium oral tablets. Neolpharma Inc, Caguas, PR, 2026. DailyMed
- Product Information: SYNTHROID(R) oral tablets, levothyroxine sodium oral tablets. AbbVie Inc (per FDA), North Chicago, IL, 2024. DailyMed
- de Groot JWB, Zonnenberg BA, Plukker JTM, et al: Imatinib induces hypothyroidism in patients receiving levothyroxine. Clin Pharmacol Ther 2005; 78:433-438. PubMed
Keep reading about Levothyroxine
Keep reading about Momelotinib
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