If breast cancer is part of your story and you’re working on your weight or overall metabolic health, you’ve probably come across names like “Ozempic,” “Wegovy,” “Mounjaro,” or “Zepbound.” These medicines belong to a fast-growing class of drugs known as GLP-1 receptor agonists and they are showing up in headlines, conversations, and doctors’ offices everywhere. As their use grows, many people are wondering if they are safe after breast cancer, whether they might influence cancer outcomes and not just weight, and what researchers are currently studying to help answer those questions. 

What are GLP-1s?

Drugs such as semaglutide (Ozempic, Wegovy) and liraglutide (Saxenda, Victoza) were first approved for type 2 diabetes and later for chronic weight management. Newer agents including tirzepatide (Mounjaro for diabetes, Zepbound for obesity), also activate GIP receptors and usually cause even more weight loss. In 2025, the World Health Organization issued its first global guideline on using GLP-1 medicines for obesity, recognizing that these drugs can produce 15 to 25 percent weight loss on average and improve heart, kidney, and metabolic health when combined with lifestyle support. So, it’s no surprise that many people with breast cancer are interested. Weight and metabolism matter a lot in this disease.

For years, research has shown that excess weight and metabolic health play a meaningful role in breast cancer. Obesity at diagnosis is linked to a higher risk of recurrence and death in women with hormone receptor-positive disease, particularly those on aromatase inhibitors, and studies also show that gaining more than 10 percent of body weight after diagnosis is associated with worse survival. Major reviews, including those from ASCO, reinforce that weight management and physical activity are important parts of breast cancer risk reduction and survivorship. 

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The connection between weight management and breast cancer

The reasons run deeper than the scale. Adipose tissue can raise estrogen levels in postmenopausal women, drive insulin resistance and higher insulin and IGF-1, and increase inflammation in ways that can influence tumor behavior. These connections have fueled interest in whether intentional weight loss can improve outcomes. Lifestyle-based trials using nutrition changes, exercise, and coaching have already shown that modest weight loss of about 5 percent is both realistic and beneficial for metabolic health and quality of life. GLP-1 medicines are now being explored as another tool that may help some patients reach and sustain that kind of clinically meaningful weight loss.

Two recent studies brought together what we know so far about GLP-1 medicines in people with a history of breast cancer. Early real-world data suggest that women with early-stage breast cancer who use drugs like semaglutide or tirzepatide for diabetes or obesity tend to lose about 4 to 5 percent of their body weight over a year and tolerate the medications about as well as the general population. Many of these patients are also on endocrine therapy, which makes the tolerated side effect profile particularly relevant. 

An ASCO abstract reported clinically meaningful weight loss in early-stage patients using GLP-1 drugs with no immediate signal of higher recurrence risk, and an update from Memorial Sloan Kettering described similar results, noting that even a 5 percent weight loss may help counter treatment-related weight gain. A separate review from Yale concluded that GLP-1 medicines appear safe so far in survivors, including those on endocrine therapy, with no clear increase in recurrence in early observational studies. The main concerns remain the expected gastrointestinal side effects, the possibility of overly rapid weight loss, and the risk of losing muscle in patients who may already be vulnerable. Experts generally agree that there are no obvious cancer-related safety red flags at this point, but also that stronger long-term data are still needed.

GLP-1s and breast cancer

Scientists are also exploring whether GLP-1 drugs could influence breast cancer biology in ways that go beyond weight loss. Early laboratory studies show that GLP-1 agonists like exendin-4 can slow the growth of breast cancer cells and increase programmed cell death, and a 2025 mouse study found that tirzepatide slowed the growth of obesity associated breast tumors. These findings come from cells and animals rather than people, but they point to possible mechanisms that include improved insulin and IGF-1 signaling, reduced inflammation, and in some cases direct effects on GLP-1 receptors found on certain breast cancer cells. This science is promising and helps justify clinical trials, though it is far too early to say that GLP-1 drugs directly treat breast cancer.

Two important clinical trials are now underway to answer the question many breast cancer survivors are asking: if GLP-1 medicines help me lose weight, could that lower my risk of recurrence? These studies are designed to move us from early observational signals to real evidence that can guide care.

FITWISE is one of the most closely watched trials. Led by Rutgers Cancer Institute and RWJBarnabas Health, it focuses on early-stage, hormone receptor positive, HER2 negative breast cancer survivors. The study uses tirzepatide to explore feasibility, safety, cardiometabolic changes, weight loss, and early signals related to recurrence risk during survivorship.

TRIM-EBC, a first-of-its-kind study directly testing whether medically assisted weight loss with tirzepatide can influence recurrence in people with a history of early breast cancer and overweight or obesity. Rather than looking only at weight or metabolic markers, this trial asks the core question of recurrence head-on.

These studies will take time to complete, but they represent the shift from curiosity to rigorous testing. They are the work needed to transform GLP-1 use in breast cancer survivors from a promising idea into an evidence-based standard of care.

We are entering a moment where metabolic health, cancer biology, and new drug technologies are intersecting in ways that could meaningfully change active treatment into survivorship. As studies read out, patients will need clear, unbiased explanations of what the findings really mean. Outcomes4Me was designed for that exact purpose.

By using the app, you can stay connected to the latest evidence, explore clinical trials that match your profile, and get tools that help you advocate for the care you deserve.