If you’ve been diagnosed with type 2 diabetes, metformin may be the first medication your doctor recommends. Research has found that it helps with blood sugar control and helps the body use its own insulin better.
Studies have also shown that many people taking the drug lose some weight. That’s different than many other diabetes drugs, some of which cause weight gain. It's one reason metformin helps prevent diabetes in people who are overweight and at risk for type 2 diabetes. But the medication isn’t considered a weight loss pill.
How Metformin Works
Metformin starts to work in your gut. Some scientists think it changes the balance of the natural bacteria in your digestive system. It also turns on specific enzymes that help the body use fat more effectively.
Scientists have also been trying to understand how metformin leads to weight loss. Because it alters gut bacteria, digestive issues are common side effects. So one early theory was that stomach pain caused people to lose their appetite and eat less, or that they lost water weight from diarrhea. But most of these side effects go away in a few weeks. People who lost weight on metformin continued to lose pounds after that time.
A more likely explanation is that metformin’s changes in the gut tamp down appetite. It may raise the body’s levels of the hormone leptin, which makes you feel full. Since your appetite isn’t working overtime, you eat less.
The weight you lose on the drug comes mostly from fat stores, not the mix of fat and lean muscle that happens with dieting. People on metformin also saw lower waist measurements and waist-to-hip ratios, two ways to measure body fat.
Is Metformin an Effective Weight Loss Pill?
No. The amount of weight you’re likely to lose is low. In one diabetes prevention study, 29% of people lost 5% or more of their body weight and just 8% lost around 10%. On average, that was about 5 pounds. That might be enough to start to improve your health, but not enough to make a big impact if you’re overweight. Metformin is not going to make the difference for someone who needs to lose 30 pounds or more, for instance.
That study also included a group of people who made diet and exercise changes instead of taking the drug. Of the 29% who lost weight on metformin, just over half kept it off for the next 14 years, but so did nearly half of the people who lost about the same amount of weight with diet and exercise. So the long-term weight loss success rate for metformin isn’t much different than for lifestyle changes, which have other health benefits, like improving your heart's health.
So metformin is a drug to treat or delay diabetes, not to lose weight. It’s best to think of any pounds you shed as a happy side effect. Also, metformin isn’t a substitute for healthy eating and regular exercise. In fact, experts recommend that anyone who starts the medication make both those lifestyle changes at the same time.