Metformin for weight loss: is it worth it?

Ozempic may be hogging all the headlines, but it’s not the only diabetes medication that can help people lose weight. There’s also metformin for weight loss. This oral tablet (brand names: Glumetza and Fortamet) has been helping people with type 2 diabetes lower their blood sugar for decades — and it can help with weight loss. 

But, how much weight can you lose on metformin, really? We look into that and more, including the pros and cons of taking metformin for weight loss. 

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How does metformin work for weight loss?

If you’re wondering why you haven’t heard of metformin for weight loss, there’s a reason. It isn’t approved by the U.S. Food and Drug Administration (FDA) as a weight loss medication. Instead, it’s 1 of the most popular drugs for type 2 diabetes in adults and children ages 10 and up. When used with diet and exercise, metformin helps people with type 2 diabetes control their blood sugar levels. 

Clinical trials show that metformin also leads to weight loss, but researchers don’t yet understand exactly how it does so. Metformin may work for weight loss by: 

• Reducing your appetite
• Helping you feel full sooner
• Increasing your insulin sensitivity
• Reducing the amount of glucose (sugar) your body absorbs from the food you eat
• Changing your gut microbiome (the natural bacteria in your digestive tract)
• Affecting the appetite centers in your brain
• Making you feel less like eating due to the drug’s side effects, such as nausea or diarrhea

That’s the high-level view of how metformin causes weight loss. Let’s break it down a bit further. Primarily, metformin may cause weight loss by reducing your appetite, so it’s easier to eat less and take in fewer calories. When you eat less, you tend to lose weight. 

Also, research suggests metformin causes changes to your gut microbiome, such as increasing your good bacteria and lowering bad bacteria. It also lowers glucose production, which rebalances your blood sugar levels. Combined, these effects may further regulate your appetite and cravings for certain foods. 

Metformin also affects the parts of your brain that control your appetite. It may increase hormones that reduce hunger. For example, a study in mice found that metformin increases the production of an anti-hunger hormone that’s typically released after vigorous exercise. 

It’s also possible that metformin’s side effects — which include diarrhea, nausea, and vomiting — simply make you want to eat less.

How much weight can you lose on metformin?

Weight loss with metformin tends to be modest. After 1 year, about 3 in 10 people taking metformin lost at least 5% of their body weight — a major milestone that can drive real health benefits. On average, people lose around 4.5 to 7 pounds on metformin. 

Research shows that people who lose weight on metformin may be more likely to keep the weight off. The Diabetes Prevention Program observed participants over a 15-year period. During the first year, they were split into 3 groups. The first group took metformin, 1 took a placebo, and 1 adopted a reduced-calorie diet in addition to walking for 150 minutes per week. 

Over 28% of the metformin participants lost at least 5% of their body weight after 1 year. That’s more than double the amount of participants who underwent lifestyle changes alone. When compared to their baseline weight, people taking metformin averaged 6% weight loss. They were also most likely to keep the weight off over the next 15 years. 

When compared to weight loss injections, you’ll likely lose less weight with metformin. On average, people taking:

• Wegovy (semaglutide) lose almost 15% of their body weight within 1.5 years
• Ozempic (semaglutide) lose at least 5% (and sometimes more than 10%) of their body weight within 10 months
• Mounjaro (tirzepatide) lose nearly 14% of their body weight within 1 year
• Zepbound (tirzepatide) lose nearly 21% of their body weight within 1.5 years

The amount of weight loss you experience on any medication — whether it’s metformin, a prescription weight loss pill, or a GLP-1 agonist — depends on other lifestyle changes you make. Usually, that includes eating a healthy, reduced-calorie diet, moving more, and quitting drinking or smoking. 

Underlying health conditions may also affect the weight you lose on metformin or another weight loss drug. For example, people with type 2 diabetes tend to lose less weight on weight loss medications than people without diabetes.

How long does it take metformin to work for weight loss?

Around 1 in 3 people lose at least 5% of their body weight after taking metformin for 1 year — that’s about 6 pounds and nearly 1 inch off their waistlines. Some may notice significant weight loss even sooner. In 1 study, people with type 2 diabetes lost around 2 pounds within 1 to 3 months of taking metformin. 

What are the benefits of metformin for weight loss?

Metformin can reduce your appetite, causing you to eat less and potentially lose weight. It’s also been used to help prevent weight gain in people who gain weight when taking antipsychotics, although this is still an off-label use. But even the blood sugar-lowering effects of metformin may hold benefits for weight loss. 

If you have diabetes, your body produces more glucose (sugar). As your blood sugar rises, your body needs more insulin to regulate it. But when there’s too much glucose to deal with, insulin encourages your fat cells to take it in — leading to bigger fat cells and a need for more of them. Over time, this leads to obesity and insulin resistance, while also making it tougher to lose weight. By rebalancing your blood sugar levels, metformin can help you lose weight more successfully.

Other benefits of metformin

Metformin offers other health benefits, including anti-cancer and anti-aging benefits. Increased insulin sensitivity can help you age better, potentially reversing some of the negative effects obesity has on aging. Metformin can also improve your gut microbiome, by boosting your levels of healthy bacteria and lowering levels of bad bacteria. 

Metformin may have therapeutic potential for several cancers, including breast, endometrial, bone, colorectal, and skin cancer. It’s also been studied for treating liver, heart, and kidney diseases. And, it may even improve brain function, which may protect against Alzheimer’s or Parkinson’s disease.

How do you take metformin for weight loss?

Metformin is available as immediate-release and extended-release oral tablets, as well as an oral liquid solution. Forms and available strengths are as follows:

There isn’t specific dosage guidance for taking metformin for weight loss, since it’s an off-label use. If your healthcare provider thinks metformin is right for you, they’ll determine the best dosing schedule. Generally, you start with a lower dose and increase over time. 

With immediate-release metformin, you may start by taking 500 milligrams twice a day, or 850 milligrams once per day, always with a meal. The maximum dosage of the immediate-release version of metformin is 2,550 milligrams per day, split into smaller doses that you take 2 or 3 times per day with meals.

With the extended-release version of metformin, you may start with 500 milligrams, taken once per day with dinner. The maximum dosage of extended-release metformin is 2,000 milligrams, taken once per day.

What are the cons of metformin for weight loss?

Metformin is an affordable and effective medication that can be prescribed off-label for weight loss. It’s also considered a safe weight loss pill. But it may have some downsides, depending on your personal health situation.

Not everyone can get a metformin prescription

Because metformin is FDA-approved for diabetes, taking it for weight loss is considered an off-label use. Off-label prescribing is common, especially in weight management. But it can make it more difficult to get a medication covered by your insurance plan. 

Insurance companies often require prior authorization before covering metformin for weight loss. If you’ve never had to do that before, it involves submitting paperwork to your insurer with the help of your healthcare provider. And, they still might not approve your request — although you can always appeal a prior authorization denial. 

If you can’t get insurance coverage for metformin, you can pay out of pocket. Generic metformin isn’t too expensive. The immediate-release version has an average out-of-pocket cost of $10 to $30 for 30 tablets, according to drugs.com with its discount card. This equates to a 2-week or 4-week supply, depending on whether you’re taking immediate- or extended-release metformin. 

Side effects of metformin

The most common side effects of metformin include diarrhea, nausea, vomiting, flatulence, asthenia (general weakness or lack of energy), indigestion, abdominal discomfort, and headache.

While rare, metformin can cause serious side effects, including a vitamin B12 deficiency and hypoglycemia (low blood sugar). Your healthcare provider will likely monitor your B12 levels while you take metformin to ensure they stay within a healthy range. If you have diabetes and use insulin, you may be more likely to experience hypoglycemia when taking metformin. Your healthcare provider may lower your insulin dose to prevent this from happening.

Other considerations when using metformin

Here are a few more things to keep in mind when using metformin for weight loss.

Boxed warning for metformin

A boxed warning is the most serious warning the FDA issues to warn patients and doctors about a drug’s potentially dangerous effects. Metformin has a boxed warning for lactic acidosis, a condition where your blood becomes too acidic. Lactic acidosis can cause symptoms like nausea, vomiting, fatigue, muscle cramps, and even sepsis or shock. 

Risk factors for metformin

Some people may be more likely to experience unwanted side effects when taking metformin. This includes older adults and those with liver problems. It can also increase your chances of getting pregnant. 

Some people shouldn’t take metformin at all, including people with severe kidney issues, an allergy to metformin, or acute or chronic metabolic acidosis.

When asking your doctor for weight loss pills, always share your full medical history. This can help them decide if metformin is a safe option for you, or if another medication is better.

Interactions with alcohol

Metformin interacts with alcohol. Excessive drinking may make metformin less effective and can increase your risk of serious side effects, including lactic acidosis. Avoid drinking when taking metformin. 

Drug interactions

Metformin can interact with other medications, including:

• Carbonic anhydrase inhibitors, including topiramate (Topamax, Topiragen)
• Ranolazine (Ranexa)
• Vandetanib (Caprelsa)
• Dolutegravir (Tivicay)
• Cimetidine (Tagamet)
• Furosemide (Lasix)
• Nifedipine (Procardia, Adalat)
• Digoxin (Digox, Lanoxin)

Give your healthcare provider a full list of any medications you are taking. Include prescription medications and over-the-counter (OTC) supplements and vitamins.

Key takeaways

• Metformin is FDA-approved to treat type 2 diabetes. It may also be prescribed off-label for weight loss.
• Metformin helps with weight loss by reducing your appetite, increasing insulin sensitivity, changing your gut microbiome, and affecting your brain’s appetite centers. 
• Metformin causes a modest amount of weight loss and can help with long-term weight maintenance. On average, 1 in 3 people taking it lose at least 5% of their body weight in 1 year.
• You may lose less weight on metformin than on medications like Ozempic, Wegovy, Zepbound, and Mounjaro.
• Pros of Metformin include possible anti-aging and anti-cancer benefits. It’s also affordable. Cons include gastrointestinal (GI) side effects and difficulty getting insurance to cover it for weight loss. 

Is metformin for weight loss right for you?

On Klarity, talk to a provider about metformin or another weight loss medication in as little as 24 hours. Find a provider on Klarity and start your weight loss journey today. 

Sources

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The information provided in this article is for educational purposes only and should not be construed as medical advice. Always seek the guidance of a qualified healthcare professional with any questions or concerns you have regarding your health.

How we reviewed this article: This article goes through rigorous fact-checking by a team of medical reviewers. Reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the author.