A new study has found that several common medications taken by millions of Australians may be linked to poorer outcomes for breast cancer patients.

Researchers from the University of South Australia and Flinders University discovered that some widely prescribed drugs—including those used for heartburn, high blood pressure, and cholesterol—may influence how patients respond to cancer treatment. However, they stressed that no one should stop taking their prescribed medication without medical advice.

The study, published in Cancer Medicine, found that proton pump inhibitors (PPIs)—commonly used to treat indigestion and acid reflux—were associated with poorer overall survival rates among breast cancer patients and a 36% higher risk of severe treatment-related side effects.

Researchers suggested that PPIs may interfere with the body’s immune system or alter how cancer drugs are metabolized, though further research is needed to confirm this link.

Medications prescribed for heart disease and hypertension—such as beta-blockers, ACE inhibitors, angiotensin receptor blockers (ARBs), and calcium-channel blockers—were also linked to a higher incidence of severe side effects but did not appear to affect overall survival.

Meanwhile, drugs like statins (for high cholesterol) and metformin (for diabetes) showed no significant impact on survival or treatment side effects.

The findings were drawn from 19 major clinical trials involving more than 23,000 participants, sponsored by pharmaceutical companies including Lilly, Pfizer, and Roche, making it one of the largest analyses of its kind worldwide.

Lead author Dr. Natansh Modi said the results highlight the complex relationship between everyday medications and cancer outcomes.

“Many women with breast cancer are also managing other chronic conditions such as high blood pressure, diabetes, or acid reflux, meaning they often take multiple drugs at once,” Dr. Modi explained.
“Our results don’t suggest people should stop their regular medications, but they do show how important it is for doctors to regularly review all prescriptions.”

Corresponding senior author Associate Professor Ashley Hopkins of Flinders University emphasized that cancer patients taking PPIs deserve particular attention.

“This doesn’t mean patients should stop their reflux medication without consulting a doctor,” he said, “but clinicians should review whether PPIs are genuinely necessary and consider potential risks.”

The researchers said the study underscores the need for a more holistic approach to breast cancer treatment—one that carefully considers all medications a patient is taking to avoid harmful interactions. They also called for follow-up studies to better understand the biological mechanisms behind these effects and to develop clinical guidelines for the safe co-prescription of non-cancer drugs during cancer therapy.

According to government estimates, more than 20,000 Australians will be diagnosed with breast cancer this year, and around 3,353 are expected to die from the disease.