Can Mounjaro or Wegovy Cause Cancer?

During preclinical testing, both tirzepatide and semaglutide were associated with thyroid C-cell tumours in rodents at high doses. This is a known class effect of GLP-1 receptor agonists in animal models. However, regulatory and scientific bodies have noted that rodents develop these tumours through a mechanism that does not appear to operate in the same way in humans, and no causal link to thyroid cancer in people has been established based on current evidence.

What this means in practice

Because of the animal findings, people with a personal or family history of medullary thyroid carcinoma (MTC), or those with a condition called Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), are generally considered unsuitable candidates for these medicines. Suitability is always assessed by a prescriber — it is not something to judge independently.

For the broader population of people already prescribed these medicines, the available human evidence collected so far has not demonstrated a causal link between tirzepatide or semaglutide and cancer. Ongoing post-market surveillance continues to monitor for safety signals, as it does with all prescription medicines. Any new concerns would be reflected in updated product information and communicated by medicines regulators.

How side effects and safety concerns are reported

If you notice any new or unusual symptoms while taking Mounjaro or Wegovy, you can report them to your national reporting scheme — such as the UK's Yellow Card scheme — as well as raising them promptly with your prescriber or doctor. Post-market reporting plays a real role in detecting rare signals that clinical trials may not capture.

You can read further about the factual mechanism of these medicines in our overview of how Mounjaro works. Related questions our community often explores include more detail on Mounjaro and cancer risk and what current evidence says about Mounjaro and cancer.

When questions about long-term safety arise, keeping a detailed personal record of how you feel over time has real value. GLP Trackr's side-effect and symptom logging lets you note any new or persistent symptoms — including things that feel unusual or hard to describe — along with the date, severity, and context, so you have a clear picture to bring to your prescriber or doctor rather than relying on memory.

Spotting patterns over time is where the app's insights become genuinely useful: you can see how your reported symptoms relate to dose timings, food, sleep, and other logged data. If something shifts, you have a record. That record can inform a more productive conversation with your healthcare team — not replace it.

GLP Trackr also helps you stay consistent with your weekly injection schedule through dose reminders and shot logging, so nothing is missed or forgotten between appointments. You can also explore other commonly asked questions about what Mounjaro can cause as you get to know how your body responds.

Important: GLP Trackr is a tracking and journaling companion — it does not provide medical advice, assess your individual risk, or replace the guidance of your prescriber or doctor. If you have any concerns about cancer risk or any new symptoms that worry you, contact your healthcare professional promptly. They can review your full medical history and give you advice tailored to you.

Log your symptoms, track your journey, and go into every appointment better prepared. Download GLP Trackr free on the App Store or Google Play — your first 7 days are on us.