Common Diabetes Drug May Diminish Exercise Benefits, Study Finds
New research suggests that metformin, one of the most widely prescribed drugs for diabetes, may interfere with some of the health benefits normally gained from exercise.
Metformin is the first-line medication for managing high blood sugar, with nearly 86 million prescriptions filled in the United States in 2023. Doctors have long recommended that patients take metformin alongside regular exercise, assuming the two proven therapies would work better together. However, a new study indicates that this combination may not be as effective as once believed.
“Most health care providers assume one plus one equals two,” said lead author Steven Malin, a professor at Rutgers University. “The problem is that most evidence shows metformin blunts exercise benefits.”
This finding is concerning because many people who take metformin are overweight or have diabetes and rely on exercise to help control blood sugar, improve fitness, and reduce long-term health risks.
Dr. Betul Hatipoglu, a professor of medicine at Case Western Reserve University School of Medicine who was not involved in the research, told that this is the first study to show metformin may reduce improvements in blood vessel insulin sensitivity—one of the key benefits typically gained through exercise.
How Metformin May Reduce Exercise Gains
Researchers at Rutgers University examined how metformin affects the benefits of exercise on blood vessel function, physical fitness, and blood sugar control. The study, published in The Journal of Clinical Endocrinology & Metabolism, involved 72 adults at risk for metabolic syndrome—a cluster of conditions that increases the likelihood of developing diabetes and heart disease.
Participants were divided into four groups:
High-intensity exercise with a placebo
High-intensity exercise with metformin
Low-intensity exercise with a placebo
Low-intensity exercise with metformin
Over 16 weeks, researchers tracked changes in blood vessel function, which plays a critical role in delivering oxygen and nutrients to muscles after meals.
The results showed that exercise alone significantly improved insulin response. Blood vessels became more sensitive to insulin, allowing greater blood flow to muscles and helping lower blood sugar levels after eating. Exercise also reduced inflammation and fasting blood sugar.
However, when metformin was combined with exercise, these improvements were noticeably reduced. Participants taking metformin also experienced smaller gains in overall fitness.
“Exercise is crucial for lowering blood sugar and improving physical function—both major goals in diabetes treatment,” Malin said. “If metformin interferes with these benefits, patients may not get the full protective effects.”
“If you exercise and take metformin and your blood glucose does not go down, that’s a problem,” he added. “People taking metformin also didn’t gain fitness. That means their physical function isn’t improving, which could raise long-term health risks.”
Malin also pointed to earlier research showing that metformin can limit muscle gains from weight training. “This suggests metformin may interfere with both endurance and resistance exercise when it comes to health outcomes,” he said.
Important Context and What This Means for Patients
Researchers emphasized that metformin remains an effective and important treatment for diabetes. The study does not suggest people should stop taking the drug or stop exercising. Rather, it highlights how taking both at the same time may reduce the benefits of exercise.
The findings apply specifically to situations in which patients begin exercise and metformin simultaneously. Other studies suggest that people who take metformin first and then add exercise later may see greater improvements than those who remain on medication alone.
Malin explained that the body may adapt to metformin over time, allowing exercise to act as a new stimulus that drives further improvement. However, no studies have yet directly compared long-term outcomes between starting both treatments together versus introducing one after the other.
“More research is needed to determine how best to prescribe these two therapies together,” Malin said.
Why This Might Be Happening
The exact mechanism behind metformin’s effect on exercise benefits is not fully understood. Malin noted that metformin partially blocks activity in mitochondria—the cell’s energy centers—which helps reduce cellular stress and improve blood sugar control.
However, this same action may also interfere with exercise-induced changes in cells, such as mitochondrial growth and improvements in aerobic capacity.
The implications are significant. Nearly 35 million Americans have Type 2 diabetes, and prevention strategies often rely on both lifestyle changes and medication. If these approaches do not work together as expected, the risk of complications may increase.
While metformin is effective for managing blood sugar, Malin said combining it with exercise “may not be better than either treatment alone” in some cases.
Ultimately, the researchers stress that patients should continue following medical advice. The study underscores the need for doctors to closely monitor patients and carefully consider how exercise and medication are combined. Future research may help identify strategies that preserve the benefits of both.
