Weight-loss drugs linked to lower breast cancer rates. What to know

Obesity is a known risk factor for breast cancer, so could some women reduce their odds of this common type of cancer by taking weight-loss drugs such as Wegovy and Zepbound?

A study of more than 111,000 women published June 2 in a peer-reviewed journal found that those who took popular GLP-1 drugs prescribed for obesity or diabetes had a more than 30% lower risk of breast cancer. But researchers cautioned that the observational study doesn't prove the popular weight-loss drugs reduce cancer risk.

Along with research released in May that found GLP-1 users were less likely to see some obesity-related cancers spread, University of Pennsylvania researcher Elizabeth McDonald said her study linking breast cancer prevention to GLP-1 drugs should "only increase the possibility there's a real biological signal" that should be studied in a robust clinical trail.

Other than skin cancer, breast cancer is the most common cancer among U.S. women, accounting for an estimated 380,000 cases per year. About one in eight women will be diagnosed with breast cancer over their life.

If GLP-1 drugs helped lower risk of breast cancer, "the benefits would be transformative for women's health," said McDonald, a professor of radiology at the University of Pennsylvania Perelman School of Medicine.

What researchers know about GLP-1s and breast cancer

McDonald presented her findings at the American Society of Clinical Oncology meeting, and the study was published June 2 in the medical journal JCO Oncology Practice. The study examined the health records of more than 111,000 women ages 45 to 80 who were overweight and had breast imaging done at Penn Medicine facilities.

The health records, which spanned from 2022 through mid-2025, showed that more than 15,000 of the women had a prescription for GLP-1 medications, while more than 96,000 had no records of GLP-1 prescriptions. Researchers compared the two groups and discovered that the women prescribed GLP-1 medications had a 35.1% lower risk of developing breast cancer.

Researchers also analyzed records to match the 15,000-plus GLP-1 users to a control group of non-GLP-1 users. The groups were matched across age, race, ethnicity, body mass index, breast density and diabetes status. When researchers compared the two groups, those who had been prescribed GLP-1 drugs were 30.5% less likely to be diagnosed with breast cancer.

The study didn't specify the type of GLP-1 medications used or how long the women took the weight loss or diabetes medications. The study also didn't account for genetic risk factors or whether cancers had reached an advanced stage at the time of diagnosis.

And because the study relied on health records of women who visited Penn facilities, it didn't address whether patients got GLP-1 medications elsewhere such as a telehealth company or a compounding pharmacy. During the study period, consumers flocked to telehealth providers and compounders who sold less-expensive knock-off versions of GLP-1 weight-loss drugs.

If study participants secured GLP-1 drugs through telehealth providers or compounders, "we would have no idea they were on the drugs," McDonald said. "This would dilute the effect, because you would have people on the GLP-1 in the control group."

McDonald and other researchers are seeking funding to launch a clinical trial to gauge whether GLP-1 drugs can decrease breast cancer cases among women at high risk. The study, designed to track participants over five years, also would seek to answer whether GLP-1 drugs can lower the risk of tumors returning in women who've previously had breast cancer.

Researchers not involved in the University of Pennsylvania study said it contributes to growing research involving GLP-1 drugs commonly prescribed for weight loss and to treat Type 2 diabetes. Some GLP-1s are approved for sleep apnea and to reduce heart disease risk. And researchers are studying their potential for addiction treatment and cancer.

"I think we're going to see potential usefulness for cancer survivorship, and maybe cancer prevention, with some of these newer (weight loss) medications coming on the market," said Bernard Fuemmeler, an associate director for population sciences at Virginia Commonwealth University (VCU) Massey Comprehensive Cancer Center.

In May, VCU researchers published a study in JAMA Network Open that suggested breast cancer patients who used GLP-1s had better outcomes than those who didn't take the medications.

The VCU study of more than 840,000 patients matched similar groups of breast cancer patients who had obesity or Type 2 diabetes. Those patients who took GLP-1s had a higher survival rate after 10 years and were less likely to have tumors return compared to non-users.

Past research has shown that breast cancer patients who lose weight through treatment or surgery have improved heart health and longevity. Researchers said it therefore makes sense that weight loss from GLP-1 use could deliver better results for breast cancer patients.

"If we can figure out ways to reduce the risk of cancer among people who have (greater) risk factors, that's the key to what we want to do in cancer prevention," Fuemmeler said.