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FDA Requiring Lilly to Monitor Mounjaro Medullary Thyroid Cancer Risk

This week, the FDA submitted phase 4 clinical trial requirements to Eli Lilly. In one study, Lilly will monitor infants who are given breastmilk from mothers who are actively using Tirzepatide. The second study will follow incidences of medullary thyroid cancer.

Phase 1 trials showed that lab rats who were administered large doses of Tirzepatide daily, developed thyroid cancer, but this risk has never been clearly established in human trials. In fact, rats possess a GLP-1 receptor in their thyroid that humans do not, making this information trickier to decipher. Now the FDA wants Lilly to monitor numbers of cases to assess any potential risk.


FDA Eli Lilly Letter
Download PDF • 210KB

In this particular study, researchers will collect and analyze data on cases of medullary thyroid carcinoma (a type of thyroid cancer) in the United States for at least 15 years. The main goals of the study are to:

  1. Track the number of new cases of medullary thyroid carcinoma that occur each year (annual incidence).

  2. Investigate if there is any increase in the number of cases after the introduction of tirzepatide, a medication used to treat diabetes, into the market.

  3. Create a registry to keep records of new cases of medullary thyroid carcinoma and gather information about the patients' medical history, particularly regarding diabetes and the use of tirzepatide.

By doing this study, researchers aim to understand whether there's any association between tirzepatide and an increased risk of medullary thyroid carcinoma in the United States.

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