Does Metformin Cause Weight Loss?

Medically Reviewed by Jabeen Begum, MD on December 28, 2023
6 min read

If you’ve been diagnosed with type 2 diabetes, metformin may be the first medication your doctor recommends. Research shows that it helps with blood sugar control by helping the body use its own insulin better.

Studies have also shown that many people taking the drug lose some weight. That's one reason metformin helps prevent diabetes in people who are overweight and at risk for type 2 diabetes. The FDA hasn't approved metformin for weight loss . But some doctors do prescribe it for that purpose. This is called off-label use.

Doctors aren’t entirely sure how metformin works to help you lose weight, but they suspect it’s a combination of things. Perhaps most importantly, it helps reduce your appetite. It does this in part by increasing levels of hormones that help you feel less hungry. It also:

  • Limits how your liver produces glucose so that you may need less insulin

  • Improves insulin resistance so the insulin your body produces works better 

  • Changes your gut microbiome, the microorganisms in your digestive system that help break down food

All of these things are also thought to play a role in weight loss.

Metformin isn’t a magic weight loss pill, but it could help you lose a modest amount of weight as well as prevent weight gain.

You likely won't lose as much weight as you would with some other diabetes drugs, such as semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro, Zepbound). The FDA has approved Wegovy and Zepbound for treating weight loss.

In a long-term study involving over 3,000 people, the average weight loss for participants who took metformin was 5.5 pounds. About one-third of those who took metformin lost at least 5% of their body weight after a year. And the longer they took it (up to 15 years), the better the results, with an average long-term loss of 6.2% of body weight. 

But so far, metformin's weight-loss effects haven't been consistent enough for it to be considered a weight-loss drug. And it can't replace a healthy diet and regular exercise.

Most people who take metformin have type 2 diabetes. If you have type 2 diabetes, weight loss can slow down the disease.

Others who might be prescribed metformin for weight loss may include those who:

  • Have obesity, which doctors define as having a body mass index (BMI) of 30 or more. Studies show that even if you don’t have type 2 diabetes but have obesity, metformin can help with weight loss. Weight loss helps reduce your risk of developing type 2 diabetes.
  • Have insulin resistance, a condition in which your body makes the blood-sugar regulating hormone insulin but can't use it correctly. Metformin helps your body react to the insulin your pancreas produces.
  • Take antipsychotic medications. Some of these medications cause weight gain, which increases the risk of type 2 diabetes and other health problems such as high cholesterol. Metformin may help prevent weight gain if you take it when you're on antipsychotic medications.

Metformin and PCOS

Polycystic ovary syndrome (PCOS) is a hormonal condition that affects as many as 5 million women (and those designated as female at birth) in the U.S. More than half develop type 2 diabetes by the time they're 40. PCOS also causes issues with your monthly cycle, can lead to pregnancy complications, and is a common cause of infertility. Not only can metformin help prevent weight gain in those with PCOS, but it may also help:

  • Restore ovulation
  • Reduce the amount of androgen, the male hormone responsible for many PCOS symptoms, in your body
  • Reduce your risk of miscarriage
  • Reduce your risk of gestational diabetes (diabetes during pregnancy)

Metformin can be a helpful drug for many people, but not everyone should take it. Your doctor may not prescribe metformin if you:

  • Have uncontrolled diabetes
  • Are allergic to the drug
  • Have a serious infection
  • Recently had a heart attack
  • Have heart failure
  • Have trouble breathing
  • Have blood circulation problems
  • Drink alcohol often or in large amounts 

If you have serious kidney disease, your doctor probably won't recommend metformin. That's due to an increased risk of a rare but serious condition called lactic acidosis. But you might be able to take it if your kidney disease is in the early stages and your doctor thinks metformin is the best drug for you.

Previously, doctors didn't prescribe metformin to people with congestive heart disease or chronic liver disease. But experts now believe some people with these conditions can take metformin, as long as they're watched carefully to avoid complications.

Make sure your doctor knows about all the medications you take. Metformin could interact with acetazolamide (Diamox), dichlorphenamide (Keveyis), methazolamide, topiramate (Topamax Qsymia), or zonisamide (Zonegran).

As with many medications, your metformin dose will depend on your health. Most people take a step-up approach: Your doctor prescribes a lower dose, then gradually increases it or adds another medication until your blood sugar levels reach safer levels.

Your dosage also depends on what type of metformin you take:

  • Immediate-release: If you take this type of pill, you may start at 500 milligrams once or twice a day. Or you might take a once-daily dose of 835 milligrams. If necessary, your doctor can slowly increase this to a target dose, called a maintenance dose, of 850 or 1,000 milligrams twice daily.
  • Extended-release (capsules): You usually take these once a day at first, either 500 or 1,000 milligrams. Your doctor can increase your dose slowly, up to a maximum of 2,000 milligrams once or twice daily.

Metformin dosage for weight loss in non-diabetes

Metformin isn't approved as a weight loss medication, so there's no labeling information about what dose you should be prescribed. However, doctors have learned what doses are likely best for their patients. In one study, people started by taking 500 milligrams daily and gradually increased to 2,500 milligrams. The average dose ended up being 2,230 milligrams per day. In another study, participants lost weight when they took 1,500 milligrams of metformin a day.

Whether you take metformin for weight loss or to treat diabetes, the medications are the same.

You take extended-release tablets once a day. Extended-release medications should never be chewed, cut, or broken up in any way. That will send too much of the drug into your system too quickly. If you have trouble swallowing your pill, ask your pharmacist about alternatives. If you keep having problems, talk to your doctor. You might need a different prescription.

You can also get metformin in standard tablets or suspension (liquid), which your body absorbs more quickly. You usually take these once or twice a day. If you are taking it in suspension form, always use an oral syringe, medication cup, or measuring spoon meant for medications. Kitchen measuring spoons aren't accurate enough for drugs.

Always take metformin with meals. It can upset your stomach or cause diarrhea when you first start taking it, but taking it with food helps reduce this effect.

Metformin is a common diabetes drug that doctors sometimes prescribe off-label for weight loss. It can help you lose modest amounts of weight and prevent weight gain. But it can't take the place of a healthy diet and regular exercise. If you're trying to lose weight, ask your doctor about the most effective methods.

How does metformin work in your body?

Metformin does several things in your body, such as reducing how much glucose (sugar) your liver releases into your body. Researchers think one of the main reasons it works for weight loss is that it affects hormones involved in appetite, leading you to eat less.

Is Ozempic more effective than metformin for weight loss?

These two medications work in different ways to control blood sugar and help with weight loss. Some studies have shown that people who take semaglutide (Ozempic) lose an average of 8.4 to 10.4 pounds. In a large, long-term study, people who took metformin lost an average of 5.5 pounds. Doctors sometimes prescribe semaglutide and metformin together. This can maximize weight loss.