Maybe you’ve heard that the diabetes drug metformin makes people lose weight. But is that even true? And more important, might you be one of the people who could drop pounds by taking this prescription medication?

Great questions. The answers are: Yes, metformin helps some people lose weight, but depending on what’s going on with your body, you may—or may not—be one of them.

Before we get to whether it makes sense for you to ask your doctor to take out her Rx pad, here’s a little background:

What is metformin?

Metformin is an oral drug that is FDA approved to control blood sugar levels in people with type 2 diabetes. It is sometimes used off-label (meaning docs prescribe it for non-FDA-approved uses it seems to work for) in people with prediabetes—i.e. they have somewhat high blood sugar or some insulin resistance, and so are at risk for developing diabetes. It’s also prescribed off-label for other conditions, such as polycystic ovarian syndrome.

And how does metformin work?

Researchers aren’t 100% sure of all the ways the drug acts in the body. “Metformin is a complex drug with multiple sites of action and multiple molecular mechanisms” that are not fully understood, according to a 2017 report.

What is known is that metformin causes the liver to lower the amount of glucose (sugar) it makes and releases into your bloodstream, and also affects your gut, so that you use glucose more efficiently. All of this helps people with diabetes, whose blood sugar is too high and/or not being used properly (which makes the body want to crank out more.)

So how does it help some people lose weight?

Folks seem to be less hungry on the drug. “Metformin mainly causes weight loss by lowering food intake,” says Steven K. Malin, Ph.D., an assistant professor and expert in exercise metabolism and human nutrition at the University of Virginia’s Curry School of Education and Human Development. Simply put, the drug is thought to act on the brain via neural pathways to lower appetite signals, and to tamp down the signals of a ghrelin, a hunger hormone manufactured in the gut, which together add up to you feeing less noshy.

It may also help your gut flora use glucose as an energy source, says Malin, which means your body doesn’t need to dip into blood glucose as frequently, causing those crazy energy dips that make you want to inhale a king-size sack of M&Ms and a Big Gulp.

Another way it is thought to make you less hungry is that metformin may reduce inflammation in your fat tissue, says Caroline Apovian, M.D., an obesity medicine physician and professor of medicine at Boston University School of Medicine. “We think inflammation begins the process of weight gain, and causes dysfunction in the neural pathways that lead to satiety in the brain,” she says. In other words, this inflammation may be preventing your brain from getting the “I’m full” signals that your hormones are trying to convey.

So metformin seems to be a one-two punch: “If you alter the gut microbiome, you’re increasing the satiety hormones,” says Dr. Apovian. “If you improve inflammation, you’re allowing the satiety hormones to work through a different mechanism—but it all ends up in the brain.” Finally, when the brain says, “step away from the Oreos,” you are no longer helpless to comply.

What is the average weight loss with metformin?

About 4 or 5 pounds, says Dr. Apovian, who prescribes metformin along with one of the approved drugs for obesity for people who have diabetes and obesity or prediabetes and obesity to help with bigger weight loss. “If someone has obesity, you always need another agent aside from metformin.” The heavier a person is, the better they are likely to drop a few pounds on metformin, and research shows that the weight loss in people with diabetes who stay on the the drug lasts.

What if you don’t have diabetes or pre-diabetes?

In some cases, “metformin can still promote some weight loss,” says Malin. “There is evidence that metformin can induce weight loss of approximately 5-10 lbs. in people who have PCOS or psychiatric disorders” such as schizophrenia, he says. “A possible reason is that they have associated insulin resistance.”

But what if your insulin is fine and you just want to lose a few pounds?

While some doctors will prescribe metformin for moderately overweight people without insulin issues, it is not clear from any research that it helps. “Unless it is warranted to take metformin to promote glycemic control or improve insulin sensitivity because of underlying health issue, taking metformin may not be advisable,” says Malin. His research on healthy people as well as people with prediabetes taking metformin and exercising had mixed findings—more fat metabolism, but blunted fitness gains and no added health benefit from taking the drug. “Focusing instead of being physically active and consuming a proper diet would like be better” for weight loss—and build healthy habits going forward.

Bottom line: If you have diabetes, pre-diabetes, insulin resistance or hyperinsulinemia (when your blood sugar is too high for a variety of reasons), or have the disease of obesity, it’s worth asking your doctor about taking metformin. If not, keep your body moving and eat healthfully, avoiding processed foods especially, as they are thought to contribute to inflammation.

Like what you just read? You’ll love our magazine! Go here to subscribe. Don’t miss a thing by downloading Apple News here and following Prevention. Oh, and we’re on Instagram too.