Study of 110,000 women links Ozempic, Wegovy, Mounjaro and Zepbound to lower breast cancer risk

Popular medicines such as Ozempic, Wegovy, Mounjaro and Zepbound may bring an unexpected advantage 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 treatments such as Ozempic and Wegovy - were significantly less likely to develop breast cancer.

The findings were presented at the 2026 Annual Meeting of the American Society of Clinical Oncology (ASCO) and published in JCO Oncology Practice. Researchers reported that women using GLP-1 medicines had around a 30% lower likelihood of developing breast cancer than women who were not taking these drugs.

“While our study is observational and does not definitively confirm an association between GLP-1 medications and reduced breast cancer incidence, it adds to a growing body of evidence suggesting these weight loss medications are worth investigating 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 Center.

Ozempic sparks interest in cancer research

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

Over recent years, several observational studies have suggested GLP-1 medicines may be linked to lower risks for certain cancers, or to improved outcomes among cancer survivors. However, researchers stress that observational research alone cannot establish cause and effect. Large, prospective clinical trials are still needed to determine whether these medicines directly reduce cancer risk.

To address that gap, McDonald and colleagues are working to launch a multi-centre clinical trial to test whether GLP-1 medicines can reduce breast cancer incidence in women considered to be at high risk, including some with a previous history of the disease.

“GLP-1 medications are interesting from a cancer research perspective because they weren’t developed for oncologic therapy, but they affect many targets and pathways associated with cancer development, so we are eager to study them in that context,” McDonald said.

Study shows lower breast cancer rates

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

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

New breast cancer diagnoses were assessed in two distinct groups. The first included the full population of 111,646 women. The second was a matched cohort of 30,528 women, where each GLP-1 user was paired with a non-user with similar characteristics such as age, race, ethnicity, BMI, breast density and the presence of diabetes. This design aimed to reduce bias and account for potential confounding factors.

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

Researchers highlighted several limitations. The study did not distinguish between specific medicines such as Ozempic, Wegovy, Mounjaro or Zepbound. It also did not account for treatment duration, genetic risk factors, cancer stage or tumour subtype. Further analyses are planned to explore some of these variables.

Why weight-loss medicines might affect breast cancer risk

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

Because GLP-1 medicines are highly effective at promoting weight loss, some of the observed benefit may be related to reduced body weight. Even so, researchers suspect additional biological mechanisms may also play a role.

Longstanding evidence has pointed to chronic, low-grade inflammation as a possible contributor to breast cancer development. GLP-1 medicines are known to reduce inflammation through multiple pathways. They also influence metabolism and may affect epigenetic processes that help regulate gene activity. At present, researchers believe these combined effects may help suppress the development of breast cancer.