Metformin has long been prescribed to help people with type 2 diabetes control blood sugar. New research from Stanford University suggests the widely used medication may also be associated with a substantial survival benefit after COVID-19 infection.

Adults who were taking metformin before catching COVID-19 had a 39% lower risk of dying during the following year than patients taking a different class of diabetes medication, researchers found. The findings were published in the journal Diabetes, Obesity and Metabolism.

The Stanford led team examined medical records from 53,332 adults in the United States who had type 2 diabetes and tested positive for COVID-19. The infections occurred between October 2021 and November 2023.

Every patient was between 30 and 85 years old. Each had received a prescription for either metformin or a dipeptidyl peptidase-4 inhibitor, also called a DPP4i, at least one month before the COVID-19 diagnosis.

Most of the patients, 50,965, were taking metformin. The remaining 2,367 patients were using a DPP4i medication.

The two patient groups differed in important ways. Metformin users had an average age of 60, while patients taking the alternative medication had an average age of 64.

After adjusting for age, gender and other variables, the researchers found that metformin users were more likely to survive during the year after infection. The association raised the possibility that metformin may have protective effects extending beyond glucose management.

High blood sugar can weaken immune defenses, according to the Centers for Disease Control and Prevention. Metformin reduces blood sugar and helps the body use insulin more effectively, although researchers have not established whether those actions account for the survival findings.

Researchers also noted that metformin may help regulate a biological pathway involved in fluid balance and blood pressure that influences COVID-19 severity. Earlier studies have indicated that the medication can reduce inflammation and lower viral levels in the body during an active infection.

The analysis initially indicated a 13% decline in long COVID symptoms among people using metformin. Further statistical testing, however, found no statistically significant association between metformin use and those symptoms.

The results are consistent with other recent research cited in the report. A University of Minnesota Medical School study found that patients prescribed metformin within six days of a COVID-19 diagnosis were less likely to die or develop long COVID.

Ziyad Al-Aly, M.D., a senior clinical epidemiologist at Washington University in St. Louis who was not involved in the Stanford study, emphasized the differences between the patient groups. Those differences may complicate comparisons of their outcomes.

"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 told Fox News Digital.

"Put simply, people on metformin are generally healthier than people on DPP-4 inhibitors," Al-Aly added. Researchers similarly noted that people receiving DPP4i medications tended to be older and have more underlying health conditions, which could have contributed to their higher mortality risk.

The Stanford review relied on existing medical records rather than a clinical trial. As a result, the study cannot establish that metformin directly caused the higher survival rate, and the researchers also lacked complete information about the patients’ COVID-19 vaccination status.

"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.

The researchers and outside expert agreed that additional clinical trials are necessary. They advised patients with diabetes not to change their medications in response to the findings.

"This is not enough evidence to change treatment," Al-Aly cautioned. "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."