A new study from Stanford University has found that people with type 2 diabetes who were taking the drug metformin before getting COVID-19 had a 39% lower risk of dying within a year of their infection, compared with patients on a different diabetes medication.
Metformin has long been a first-line treatment for type 2 diabetes, helping the body regulate blood sugar and use insulin more efficiently. The new findings, published in the journal Diabetes, Obesity and Metabolism, suggest the drug may have effects beyond blood sugar control, though researchers caution the study does not prove metformin caused the improved survival.
The Centers for Disease Control and Prevention notes that high blood sugar can weaken the immune system. It is not yet clear whether metformin’s blood-sugar-lowering effects fully explain the results. Researchers pointed to other possibilities, including that the drug may influence a biological pathway tied to blood pressure and fluid balance that can affect COVID-19 severity. Earlier research has also suggested metformin can reduce inflammation and lower viral levels during active infection.
To study long-term survival, researchers examined U.S. medical records for 53,332 adults with type 2 diabetes who tested positive for COVID-19 between October 2021 and November 2023. All participants were between 30 and 85 years old and had been taking either metformin or a different diabetes drug called a DPP-4 inhibitor (DPP4i) for at least a month before their diagnosis.
Of the group, 50,965 patients were on metformin, while 2,367 were on a DPP4i. Metformin users were slightly younger on average — 60 years old, compared with 64 for those on the alternative drug.
Who Takes Which Drug, and Why It Matters
Ziyad Al-Aly, M.D., a senior clinical epidemiologist at Washington University in St. Louis who was not involved in the study, told Fox News Digital that the two patient groups are not directly comparable.
“Metformin is the first drug most people with type 2 diabetes are given. DPP-4 inhibitors usually come later, or go to people who cannot take metformin, often because they are older or have kidney disease or other health problems,” Al-Aly said. “Put simply, people on metformin are generally healthier than people on DPP-4 inhibitors.”
After adjusting for age, gender and other factors, the researchers still found that metformin users were more likely to survive the year following their COVID-19 infection. The data also pointed to a possible 13% reduction in long COVID symptoms among metformin users, but further statistical analysis found that link was not statistically significant.
The results are broadly consistent with earlier research from the University of Minnesota Medical School, which found that patients prescribed metformin within six days of a COVID-19 diagnosis were less likely to die or develop long COVID.
“There is some evidence from the same group that metformin, started early in a COVID infection, may lower the risk of long COVID, [but] that still needs to be confirmed in large, well-designed randomized trials,” Al-Aly said.
Limitations and a Caution Against Changing Treatment
Because the Stanford analysis relied on existing medical records rather than a controlled clinical trial, the authors said it cannot establish that metformin directly caused the lower death rate. Patients taking DPP4i medications tended to be older and had more underlying health conditions, which may have contributed to their higher mortality risk. The researchers also noted they lacked complete data on patients’ COVID-19 vaccination status.
Al-Aly stressed that the findings should not change how doctors or patients approach treatment.
“This is not enough evidence to change treatment,” Al-Aly said. “People take a DPP-4 inhibitor because they need it to control their diabetes, usually because metformin was not enough or was not an option for them. No doctor is choosing between these two drugs for the same patient. The comparison in this study is not a real choice in any clinic. If you take either drug, do not change it because of this study.”
