A boxed warning has been added to the label for Mounjaro (tirzepatide), effective 2026-07-29. This significant label revision highlights the RISK OF THYROID C-CELL TUMORS. The warning explicitly states that tirzepatide causes dose-dependent and treatment-duration-dependent thyroid C-cell tumors in both male and female rats at clinically relevant exposures. It is currently unknown whether Mounjaro causes thyroid C-cell tumors in humans.
What this means
The inclusion of a boxed warning on the Mounjaro label carries significant implications for prescribing practices and patient education. Healthcare providers must now counsel patients about the observed risk of thyroid C-cell tumors in rodent studies and the current uncertainty regarding this risk in humans. This prominent warning, effective 2026-07-29, underscores the importance of a thorough discussion between clinicians and patients regarding the potential implications. While tirzepatide demonstrated the development of dose-dependent and treatment-duration-dependent thyroid C-cell tumors in male and female rats at clinically relevant exposures, the direct causal link in humans remains unestablished. The FDA's decision to add this warning reflects a commitment to ensuring that all potential risks, even those extrapolated from animal data, are prominently communicated. This ensures that patients and prescribers are fully aware of the findings and the fact that the human relevance is not yet known, facilitating informed decision-making.
Source
This information is based on an FDA label revision for Mounjaro (tirzepatide), effective 2026-07-29. The full details of the label change are available on dailymed.nlm.nih.gov.