Mounjaro and Thyroid Cancer: What Patients Should Know
Mounjaro Warnings
20 October 2025
By
Why Is There a Thyroid Cancer Warning?
If you’ve started Mounjaro (tirzepatide) for type 2 diabetes or weight management, you may have noticed a warning about thyroid cancer on the label. This can sound scary, but it’s important to know where the warning comes from, what research shows so far, and what it means for you.
The warning comes from animal studies, not from human studies. In long-term rodent studies, very high doses of tirzepatide caused thyroid tumors, including a rare type called medullary thyroid carcinoma (MTC). Because of this, regulators required a “boxed warning” on Mounjaro and other similar medications, even though we don’t know if the same effect happens in humans.
So far, there’s no clear evidence that Mounjaro causes thyroid cancer in people.
What Human Studies Show
- Regulatory safety reviews found that no cases of thyroid cancer were reported and blood tests for calcitonin (a thyroid marker) stayed normal.
- A 2024 Scandinavian study of nearly 150,000 people found no meaningful increase in thyroid cancer risk among users of GLP-1 drugs (the class Mounjaro belongs to).
- A 2023 European Medicines Agency review concluded the evidence “does not support a causal association” between these medications and thyroid cancer.
In short: the risk remains theoretical. If there is any increase, it is likely extremely small.
While the average person does not need to be alarmed, some groups should avoid Mounjaro:
- Anyone with a personal or family history of medullary thyroid carcinoma (MTC)
- Anyone with Multiple Endocrine Neoplasia syndrome type 2 (MEN2)
For everyone else, common thyroid problems like hypothyroidism or papillary thyroid cancer are not reasons to avoid Mounjaro.
What to Watch For
Your doctor doesn’t need to run routine thyroid scans while you’re on Mounjaro. But it’s important to know the symptoms of a thyroid lump and seek medical advice if you notice:
- A new lump or swelling in your neck
- Persistent hoarseness or voice changes
- Trouble swallowing or breathing
These symptoms are rare but worth keeping in mind.
The Bottom Line
If you’re worried, talk to your doctor. They can review your family history, answer questions, and reassure you about the safety of your treatment.
- The thyroid cancer warning on Mounjaro comes from rodent studies, not from people.
- Human studies so far are reassuring: no increase in thyroid cancers has been found.
- Only people with a history of MTC or MEN2 should avoid the drug.
- For most other populations, the benefits of Mounjaro for diabetes and weight loss outweigh this theoretical risk.
Takeaway: For most people, Mounjaro is a safe and effective medication. The thyroid cancer warning is more about caution than proven risk. Stay informed, monitor your health, and keep an open conversation with your healthcare team.
CutKilo’s Doctor-Led Mounjaro Weight-Loss Programme
At CutKilo, we offer a fully supervised Mounjaro weight-loss programme overseen by Dr Emil Gadimali, a UK-registered medical doctor based at 86 Harley Street.
Our approach goes beyond simply prescribing a GLP-1 medication. Every patient receives personalised medical supervision, lifestyle guidance, and progress tracking — ensuring safe, effective, and sustainable results.
Why choose CutKilo over other providers?
Because you’re not just buying a pen — you’re joining a doctor-led programme focused on long-term health improvement, not short-term fixes.
If you’re considering starting Mounjaro for weight loss, choose a service that puts your safety, results, and experience first.
Choose CutKilo – one-way path to better health.
Written by
Hanna Baldursdottir (Dietitian)
Medically reviewed by
Dr Emil Gadimali MBBS MBA
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