Ozempic, Wegovy, Mounjaro and Zepbound May Lower Breast Cancer Risk

Popular medicines such as Ozempic, Wegovy, Mounjaro and Zepbound may provide an unexpected benefit beyond helping people lose weight and manage diabetes. New research involving more than 110,000 women found that those taking GLP-1 medicines - a category that includes semaglutide-based drugs such as Ozempic and Wegovy - were significantly less likely to develop breast cancer.

The findings were presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting and published in JCO Oncology Practice. Researchers reported that women using GLP-1 medicines were around 30% less likely to develop breast cancer than women who did not use these treatments.

“Although our study is observational and does not definitively confirm an association between GLP-1 medications and a reduced incidence of breast cancer, it adds to the growing body of evidence suggesting that these weight-loss medications warrant investigation as potential cancer prevention tools,” said Elizabeth McDonald, MD, PhD, professor of Radiology at the Perelman School of Medicine at the University of Pennsylvania and a practising breast radiologist at the University of Pennsylvania’s Abramson Cancer Centre.

Ozempic fuels interest in cancer research

GLP-1 medicines mimic glucagon-like peptide-1 (GLP-1), a naturally occurring hormone that helps regulate appetite and blood sugar levels. The class covers semaglutide-based treatments including Ozempic and Wegovy, alongside tirzepatide-based medicines such as Mounjaro and Zepbound. Although they were initially developed to treat type 2 diabetes, these drugs have become among the most widely used weight-loss treatments in the United States.

Several observational studies in recent years have indicated that GLP-1 medicines may be linked to lower risks of some cancers or improved outcomes for cancer survivors. However, researchers stress that observational research alone cannot demonstrate cause and effect. Large prospective clinical trials are still needed to establish whether these medicines directly lower cancer risk.

To investigate this question, McDonald and her colleagues are working to launch a multicentre clinical trial assessing whether GLP-1 medicines can reduce breast cancer incidence among women considered at high risk, including some with a previous history of the disease.

“GLP-1 medications are interesting from a cancer research perspective because they were not developed for cancer therapy, yet they affect multiple targets and pathways associated with cancer development, so we are eager to study them in this setting,” McDonald said.

Study finds lower breast cancer rates

The research team reviewed electronic health records for 111,646 women aged 45 to 80 with a body mass index (BMI) of 25 or above who underwent breast imaging within the Penn Medicine health system between January 2022 and June 2025.

Of these women, 15,264 (13.7%) had documented prescriptions for GLP-1 medicines, while 96,382 (86.3%) had no documented exposure to these treatments.

Researchers assessed new breast cancer diagnoses across two separate groups. The first comprised the full study population of 111,646 women. The second was a matched cohort of 30,528 women, in which every GLP-1 user was matched with a non-user sharing similar characteristics, including age, race, ethnicity, BMI, breast density and diabetes status. This method was intended to reduce bias and account for potential confounding factors.

The findings were consistent across both analyses. Within the overall study population, women taking GLP-1 medicines were 35.1% less likely to develop breast cancer. In the matched analysis, the likelihood was 30.5% lower.

The researchers identified several limitations. The study did not distinguish between individual medicines, including Ozempic, Wegovy, Mounjaro and Zepbound. It also did not account for treatment duration, genetic risk factors, cancer stage or tumour subtype. Further analyses are planned to examine some of these variables.

Why weight-loss medicines may affect breast cancer risk

Scientists have long recognised that maintaining a healthy weight is an important aspect of breast cancer prevention. Excess weight, particularly after menopause, is an established risk factor for the disease.

Because GLP-1 medicines are highly effective at supporting weight loss, some of the observed benefit may be associated with reduced weight. However, the researchers suspect that additional biological mechanisms could also play a role.

Chronic low-grade inflammation has long been viewed as a possible contributor to breast cancer development. GLP-1 medicines are known to reduce inflammation through several pathways. They also influence metabolism and may affect epigenetic processes that help regulate gene activity. Researchers currently believe these combined effects may help suppress the development of breast cancer.