Does Mounjaro Cause Cancer?

There is no evidence that Mounjaro (tirzepatide) causes cancer in humans.

It’s a relatively new treatment therefore the long-term side effects are still being studied, including any potential links to cancer.

However, data from clinical trials and ongoing use suggest that most side effects are related to the digestive system, such as nausea, vomiting, diarrhoea, constipation, or reduced appetite, and often lessen over time.

Some people choose to use weight loss injections like Mounjaro to help manage obesity, which is an important step toward improving overall health. Obesity itself has been linked to a higher risk of several types of cancer, including thyroid cancer.

Before prescribing Mounjaro, your personal and family medical history, including any history of cancer, should be reviewed to assess your individual risk and determine whether the treatment is safe and appropriate for you.

Evidence from clinical studies:

Animal studies

• Very high doses of tirzepatide, the active ingredient in Mounjaro, caused certain types of thyroid tumours in rats.
• However, rats are naturally more prone to developing these types of tumours, and their thyroid cells respond differently to this class of medication than human cells do
• The dosage used in rats is far higher than what would be the equivalent dosage used in humans

Human studies

• In clinical trials involving thousands of people taking Mounjaro, no cases of medullary thyroid carcinoma (MTC) or other thyroid cancers have been reported.
• Research and safety monitoring are ongoing, but current evidence suggests no confirmed link between Mounjaro and thyroid cancer in humans.

A breakdown

Because of findings from animal studies, the manufacturer Eli Lilly and Company includes a Mounjaro thyroid cancer warning on the treatment label. 

As a precaution, Mounjaro is not recommended for anyone with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia type 2 (MEN2). 

Researchers are keeping an eye on the long-term effects of Mounjaro, as cancers can take many years to develop. 

At present, there is no proven link between Mounjaro and pancreatic cancer.

Earlier concerns came from older studies on similar diabetes medications, which suggested a possible connection.

Large clinical trials and ongoing safety reviews have not confirmed an increased risk of pancreatic cancer with these treatments.

In fact, some studies suggest these medications may have a protective effect on the pancreas, with an estimated 31% lower risk of pancreatic cancer.

However, this finding isn’t set in stone. Further research is needed to confirm whether this potential benefit is real and consistent over time.

That said, Mounjaro can, in rare cases, cause pancreatitis (inflammation of the pancreas). Although not a cancer risk, pancreatitis requires medical attention if you develop severe or persistent stomach pain.

There’s no evidence that Mounjaro causes breast cancer.

Clinical studies and post-marketing data have not shown an increased risk of breast cancer in people using Mounjaro or similar GLP-1/GIP medicines.

Most cancer concerns are based on animal studies involving thyroid tumours, not breast tissue. However, as Mounjaro new medicine, researchers continue to monitor long-term safety carefully.

If you have a personal or family history of cancer, it’s best to discuss this with your doctor or pharmacist before starting treatment.

Based on the evidence we have so far, you do not need to stop taking Mounjaro because of cancer concerns.

The safety warnings come from animal studies, and human data has not shown an increased risk.

If you are generally healthy and don’t have a history of thyroid conditions, the cancer risk from Mounjaro is theoretical, not proven.

It is important to:

• Monitor for symptoms such neck lumps, difficulty swallowing, unexpected weight loss or hoarseness
• Have regular check-ups if you are taking Mounjaro for an extended period of time
• Report anything unusual to your GP right away

There is currently no clear evidence that Mounjaro (tirzepatide) causes cancer in humans.

In clinical studies, cancer rates were similar to those seen in people who did not take the medication.

However, animal studies showed a possible risk of a rare type of thyroid tumour, which is why Mounjaro carries a safety warning about this. Having said this, human thyroid cells have fewer GLP-1 receptors.

Some research also suggests that the weight loss achieved with Mounjaro may actually reduce the risk of certain cancers.

Ongoing safety monitoring is important, and you should always tell your doctor if you or a close family member has had cancer (especially thyroid or pancreatic cancer), before starting treatment.