What Is Metformin and How Does It Work?
Metformin is a common type 2 diabetes drug that the U.S. Food and Drug Administration (FDA) has approved to treat high blood sugar, or hyperglycemia, in people with type 2 diabetes.
“[Metformin] has been considered a first-line medication in the treatment of type 2 diabetes, and it mainly acts by lowering the amount of glucose released by the liver,” says Minisha Sood, MD, a board-certified endocrinologist in New York City. “It also helps a hormone called insulin to work better by helping muscles use glucose in a more efficient manner. When insulin works better — and insulin sensitivity improves — a person’s insulin levels are lower than they would be otherwise.”
There’s no cure for type 2 diabetes, but the right combination of medication and a healthy lifestyle can stabilize blood sugar levels, according to theMayo Clinic, and in some cases even put type 2 diabetes in remission, according to astudy published in Nutrients in April 2019. This, of course, is the end goal of any diabetes treatment.
As the medication helps your body reduce your overall blood sugar levels and restore your ability to respond to insulin, you’ll not only feel better, but you may reduce the risk of future complications of high blood sugar, such as heart disease, kidney damage, nerve damage or diabetic neuropathy, and eye damage (clinically called retinopathy), the Cleveland Clinic notes.
Why Does Metformin Cause Weight Loss?
The relationship between metformin and weight is unclear, but several theories provide possible explanations for weight fluctuations.
For example, metformin may affect hunger cues. In one small study, 12 women with obesity and type 2 diabetes who were not taking insulin were randomly given two dose levels of metformin — 850 milligrams (mg) or 1,700 mg — or a placebo three times a day for three days, with each participant going through the study three times so they had each dose and the placebo. Participants received a meal test on each third day and rated their hunger level before eating. Researchers found that hunger levels in the metformin group were significantly lower, especially so with the 1,700 mg dose compared with the lower metformin dose or placebo.
Another study, published in May 2020 in the journal Diabetes Care, found that when participants increased their metformin dose by 1,000 mg or more, they lost significantly more weight than those who didn’t change their metformin dose or decrease their dose. Emerging research reported in journals including Current Obesity Reports suggests metformin may also lead to weight loss as a result of changes in the appetite centers of the brain, shifts in the gut microbiome, and reversal of metabolic changes that usually happen with age.
Then there’s the possibility that the drug’s side effects can affect your food intake. “Some people who take metformin may experience gastrointestinal side effects like nausea and diarrhea,” says Rahaf Al Bochi, RDN, a Baltimore-based media spokesperson for the Academy of Nutrition and Dietetics and the owner of Olive Tree Nutrition.
According to astudy published in the April–June 2017 Journal of Research in Pharmacy Practice, gastrointestinal side effects are a primary complaint from those who receive metformin tablets in their original formulation. The most common symptoms are vomiting, diarrhea, and nausea, which affect anywhere from 2 to 63 percent of people on the drug. Discomfort can be so severe that you may not feel like eating much and subsequently consume fewer calories. The extended-release forms of metformin have fewer documented side effects, according to a past review.
Is Long-Term Weight Loss Possible on Metformin?
Even though metformin may lead to some weight loss, the amount you lose may be far less than expected. On average, weight loss after one year on the drug is only six pounds, according to past research.
So while metformin is often given to people with high insulin levels who have difficulty losing weight, it’s not a miracle weight loss solution, says Dr. Sood. In other words, don’t expect a dramatic change in weight if you overeat and lead a sedentary life. You must follow a sensible weight loss plan with healthy eating and physical activity to see any significant change in weight.
“If someone isn’t following healthy habits, then taking metformin will not result in weight loss,” she says. “It’s important to follow a healthy diet low in refined sugars and carbohydrates if [you are] prone to high insulin levels so that maximum benefit from the medication is received.”
Keep in mind that while the number on the scale may drop while you're taking this medication, this weight loss might be temporary. You could regain pounds once you stop taking the drug and your appetite returns to normal — hence the importance of a healthy lifestyle.
And yet one study,published in May 2019 in the Annals of Internal Medicine, did find that people in the diabetes prevention program who lost at least 5 percent of their body weight after a year were more likely to maintain the weight loss long term if they were in the metformin group than if they were assigned a placebo or a lifestyle intervention.
Can People Without Diabetes Take Metformin?
What if you don’t have type 2 diabetes? Can you take metformin for weight loss? This is an excellent question, and the short answer is yes.
Sood explains that metformin has been used off-label, or outside its intended purpose as approved by the FDA, for weight management in people without type 2 diabetes.
Some evidence suggests metformin may benefit these individuals: A 2018 review examining the efficacy of metformin for weight loss in people who were overweight and had obesity without diabetes concluded that the drug significantly decreased body mass index (BMI) in adolescents and adults.
But keep in mind that this drug is available only by prescription and is not FDA approved for people without type 2 diabetes. Your doctor will likely first recommend some of these traditional strategies for weight loss:
- Get support for your emotional health.
- Avoid sugary drinks.
- Drink water before meals to fill your stomach so that you eat less.
- Exercise for 30 minutes most days of the week.
- Prepare whole foods, such as fruits, vegetables, and grains.
- Limit your intake of processed foods.
- Eat a high-protein, low-carb, low-fat diet.
- Practice portion control.
If you don’t have type 2 diabetes, your doctor may sign off on this drug if you have obesity and are struggling to lose weight. But again, metformin isn’t a substitute for healthy eating and regular exercise, which are keys to sustainable weight loss. These habits also encourage weight loss if you have type 2 diabetes but can’t take metformin.
“Some people may not tolerate metformin, so it’s important to discuss options with your healthcare provider — medication is one tool to help manage blood sugars, but diet and lifestyle changes should be discussed first, because they can significantly lower blood sugars,” says Al Bochi.
As for what diet and lifestyle changes you should consider? “Diet modifications can include being mindful of your carbohydrate intake, eating enough protein and fat at meals, choosing high fiber foods, and decreasing intake of sugar-sweetened beverages,” says Al Bochi. She also recommends consulting with a registered dietitian for tailored nutrition recommendations. “Incorporating some type of movement, such as walking, weight training, or yoga on most days is also important for blood sugar management,” Al Bochi adds.
The Bottom Line on Metformin and Weight Loss
All things considered, in some people with and without diabetes, metformin can cause a modest reduction in weight. Nonetheless, scientists are still studying why the drug has this effect. Many factors — including appetite reduction because of the drug’s side effects — are likely in play.
Ultimately, metformin isn’t a silver bullet. The most important thing you can do to lose weight, whether to manage type 2 diabetes or for some other purpose, is to make changes to your diet and lifestyle. Think of metformin as the sidekick to those steps.
Also keep in mind that the FDA has currently approved metformin only for certain people with type 2 diabetes, not for those without the health condition. If you’re taking the drug to reduce your blood sugar in the case of diabetes, keep in mind that metformin comes with side effects you’ll want to discuss and manage with your healthcare team.
Additional reporting by Leslie Barrie.