Can metformin help with weight loss? Benefits, risks, and what to know

Losing weight and keeping the weight off can be challenging, no matter who you are. Some health conditions—including obesity, type 2 diabetes, and polycystic ovary syndrome (PCOS)—can make weight loss more difficult because they disrupt the way your body stores food and uses it for energy. 

If you’ve researched weight loss methods before, you may have seen information about a diabetes drug called metformin. Though metformin wasn’t designed as a weight loss drug, research shows it may make losing weight easier for some people. 

In this article, we’ll explore how metformin works, its potential benefits for blood sugar control and weight loss, as well as side effects and safety precautions.

Metformin is a prescription medication approved for the treatment of type 2 diabetes that helps to lower blood sugar levels when diet and exercise alone are not enough to move the needle. The American Diabetes Association (ADA) considers metformin the preferred first-line diabetes drug for people 10 years or older.

Metformin is a man-made derivative of guanidine, a compound in the French lilac plant (also called goat’s rue). Metformin comes in two forms: tablet or liquid solution, both taken by mouth. 

Metformin is available as a generic or under the following brand names:

• Riomet (liquid solution)

• Fortamet

• Glucophage

• Glumetza

What is metformin used for?

Although the Food and Drug Administration (FDA) has only approved metformin for treating type 2 diabetes, healthcare providers also prescribe metformin off-label for several other purposes.

Off-label uses of metformin:

• Gestational diabetes (diabetes diagnosed during pregnancy)

• Polycystic ovary syndrome (PCOS)

• Type 2 diabetes prevention (in people with prediabetes)

• Weight management, including for people experiencing weight side effects from taking antipsychotic medications

Metformin helps lower blood glucose (blood sugar) levels, but it may also help with weight loss. Here’s a closer look at the mechanism of action for metformin and how it may aid in weight loss for certain people.

Metformin reduces glucose production in the liver

Metformin works by suppressing gluconeogenesis, which is when your liver produces glucose, raising blood sugar. Excessive gluconeogenesis means your body is producing glucose it doesn’t need and can’t use. If the body can’t use glucose, it gets stored as fat.

Metformin increases insulin sensitivity

Metformin helps make you more insulin-sensitive by activating AMP-activated protein kinase (AMPK). AMPK activation facilitates glucose metabolism and enhances the way your cells uptake glucose. This lowers your blood sugar and insulin levels. High insulin levels in the blood (hyperinsulinemia) fuel fat storage, so reducing hyperinsulinemia can help with weight management.

Metformin slows glucose absorption in the intestines

Metformin also helps by inhibiting sodium-glucose cotransporter 1 (SGLT1), and this process helps reduce glucose absorption in the small intestine. This also keeps glucose levels in check and helps prevent blood sugar spikes, which contribute to insulin resistance. People with prediabetes and type 2 diabetes have insulin resistance. Obesity and insulin resistance share connections.

Metformin reduces appetite

Metformin plays a role in increasing certain hormones and molecules in the body that help control hunger and fullness. It increases lac-phe, a molecule that exercise tends to boost. Lac-phe helps reduce hunger.

The medication also increases glucagon-like peptide-1 (GLP-1), a gut hormone that helps control blood sugar, slows gastric emptying, and decreases hunger signals to the brain. Metformin boosts growth differentiation factor 15 (GDF15) expression, a peptide hormone that helps reduce appetite.

The medication also reduces leptin resistance, which is common with obesity and overweight. Fat tissue produces the hormone leptin, which helps control hunger. However, high levels of leptin from increases in fat tissue can cause leptin resistance, where the body isn’t as responsive to the hormone. Metformin helps lower leptin levels.

Metformin reduces visceral fat

Visceral fat is the type of fat that surrounds our internal organs, and too much can be dangerous. According to human and animal studies, metformin may reduce visceral fat by boosting the oxidation (breakdown) of liver fat and increasing thermogenesis, the body’s way of burning calories to produce heat.

Metformin improves the gut microbiome

Our gut microbiome includes all the bacteria and fungi that live in the gastrointestinal tract. Metformin has beneficial effects on your gut microbiome, and these effects can help with weight management and blood sugar control.

Metformin increases the amount of beneficial bacteria and decreases others that may have a negative effect. Metformin also boosts the production of short-chain fatty acids (SFCAs). The bacteria in your gut ferment the fiber from your diet to produce SCFAs. These SCFAs then increase the production of GLP-1, which aids in weight management.

Metformin may help your cells work better

You know the saying: Mitochondria are the powerhouses of our cells. The more mitochondria we have and the better they work, the more efficient our cells are at converting the nutrients we eat into usable energy.

Mitochondrial dysfunction means mitochondria are having trouble doing their jobs. This dysfunction leads to inflammation, which can contribute to obesity and vice versa. Metformin improves mitochondrial function and combats inflammation.

The question remains: does metformin help you lose weight? The answer is maybe. There are some groups of people in which metformin shows clear weight benefits—but it isn’t a “magic pill.” 

Metformin does not replace the need for a balanced diet and adequate physical activity. At the same time, obesity is a complex chronic condition, and sometimes lifestyle changes alone are not enough to spur weight loss.

Early research on metformin was limited to people with type 2 diabetes. In those studies, participants who took metformin saw small weight loss benefits versus placebo or other diabetes medications. Other studies found metformin treatment to be “weight neutral,” meaning that people neither gained nor lost weight while taking it.

An older study from 2001 looked at the potential weight impacts of metformin in people with diabetes and morbid obesity (which this study identified as a body mass index, BMI, of 30 and above). That study found significant weight loss and a reduction in waist size after 28 weeks of taking metformin when combined with a balanced diet and exercise. The results also showed that metformin may reduce the risk factors for coronary heart disease, including high fasting insulin, leptin, and low-density lipoprotein (“bad”) cholesterol. 

Despite these promising outcomes, drawing any conclusions about metformin’s effectiveness for weight loss from this particular study is difficult. The sample size was small (only 31 participants), and the researchers didn’t include a placebo group.

Even in studies that show weight loss with metformin, the results are modest. 

One of the most extensive studies to date, performed by the Diabetes Prevention Program (DPP) and published in 2012, tested metformin in people with prediabetes. In that study, people randomly assigned metformin lost an average of 2% of their body weight. 

In that same study, 29% of people taking metformin daily lost greater than or equal to 5% or more of their initial body weight by the end of the first year, compared with 13% of people in the placebo group. About 26% of the metformin and 14% of the placebo groups had lost greater than or equal to 5% of their initial body weight at the end of year two. 

Participants’ waist circumference didn’t change much between years one and two; however, the overall weight loss results were superior to those in the placebo group. What’s more, those who lost 5% or more of their body weight were more likely to have maintained the loss at a 15-year follow-up.

One study from 2013 followed 154 people with obesity or overweight who took metformin for six months. Participants overall lost weight, and those with more severe insulin resistance lost the most weight. A 2018 review found that in 11 of 14 studies, metformin showed a greater reduction in weight and BMI when compared to placebo.

Metformin has a good safety profile. The DPP study, which looked at long-term safety, found no significant safety issues. 

Even though metformin is considered safe, some people should not take this medication. This section explores who can take it, who shouldn’t, side effects, medication interactions, and more.

Who can take metformin?

In addition to those with type 2 diabetes, other people may benefit from metformin. 

People who use antipsychotic medications

Some people taking antipsychotic medications may develop a condition called metabolic syndrome. Signs of metabolic syndrome include weight gain and elevated triglycerides and cholesterol, among others. 

In one study of people new to antipsychotics, those taking metformin saw significantly reduced weight gain, lower BMI, and improved insulin sensitivity.

People with PCOS

If you have PCOS, you may benefit from taking metformin. Characteristics of PCOS often include insulin resistance, weight gain, and hyperandrogenism, which is an excess of androgen hormones such as testosterone. PCOS can disrupt ovulation and lead to infertility. 

Some research indicates that metformin may help restore ovulation by boosting insulin sensitivity. However, we need more research on whether metformin can aid with weight loss for people with PCOS.

Who can’t take metformin?

Metformin has a black box warning from the FDA and also comes with several warnings for certain groups of people. 

You should not take metformin if you have severe kidney disease. Metformin may contribute to a life-threatening condition called lactic acidosis, which is the buildup of lactic acid in the bloodstream. This condition can affect cardiac output (how much blood your heart pumps per minute) and lead to organ failure.

If you are over 65 and have experienced any of the following, metformin might not be safe for you:

• Coma

• Diabetic ketoacidosis (blood sugar so high that it required emergency treatment)

• Excessive alcohol consumption

• Heart attack

• Heart disease

• Liver disease

• Stroke

Tell your healthcare provider if you are pregnant or plan to become pregnant before taking metformin. If you become pregnant while taking metformin, inform your provider as soon as possible.

Other conditions may affect your ability to take metformin. Tell your provider if you have had a serious infection, diarrhea, fever, or vomiting just before or after starting treatment. 

Your healthcare provider will help you determine if metformin is right for you. Be sure to be honest about your drinking habits, as alcohol consumption increases your risk of lactic acidosis.

Metformin is generally well-tolerated, but adverse effects can happen. The most common side effects of metformin include:

• Asthenia (weakness)

• Diarrhea

• Nausea/Vomiting

• Flatulence (passing gas)

• Discoloration (yellowing) of the fingernails or toenails

• Constipation

• Headache

• Indigestion

• Heartburn

• Metallic taste

Metformin may also cause a vitamin B12 deficiency over time because it potentially interferes with the absorption of this vitamin. Your healthcare provider can monitor you for any nutrient deficiencies and help you manage them. One option is B12 injections.

When to seek medical attention 

If you experience chest pain or rash when taking metformin, seek emergency treatment. These symptoms could be signs of an allergic reaction or another serious issue.

If you experience symptoms of hypoglycemia (very low blood sugar) or lactic acidosis, when taking metformin, contact your healthcare provider immediately. 

Symptoms include:

• Coma

• Confusion

• Dizziness, lightheadedness

• Extreme fatigue, weakness, or discomfort

• Fast or slow heartbeat

• Feeling cold, especially in your hands or feet

• Muscle pain

• Nausea, vomiting, stomach pain

• Numbness/tingling

• Rapid breathing or shortness of breath

• Skin flushing

• Sweating

• Tremors

Some medications may increase your risk of developing serious side effects if taken with metformin.

Potential medication interactions:

• Calcium channel blockers

• Carbonic anhydrase inhibitors like topiramate (Topamax) and acetazolamide (Diamox)

• Cimetidine (Tagamet)

• Diuretics (water pills)

• Hormone replacement therapy

• Insulin or other medications for diabetes

• Medications for asthma and colds

• Medications for thyroid disease

• Niacin

• Oral contraceptives (birth control pills)

• Oral steroids such as dexamethasone, methylprednisolone, and prednisone

• Phenytoin (Dilantin)

This is not an exhaustive list. Medications not included here may also cause possible interactions. Tell your healthcare provider about all medications (both prescription and over-the-counter), vitamins, or supplements you take before taking metformin.

Metformin is available as a generic and under the brand names Fortamet, Glucophage, Glumetza, and Riomet. It comes in both regular and extended-release formulas. It is also an ingredient in many combination therapy pills with other diabetes medications. 

The adult dosing recommendations vary by route/form and may differ depending on what metformin is being used to treat.  When used for type 2 diabetes, the dosing recommendations are:

• Immediate-release tablet: 500 mg once or twice daily, or 850 mg once daily

• Extended-release tablet: 500 mg–1,000 mg once daily

For weight loss, PCOS, gestational diabetes, or other off-label uses of metformin, the dosage varies but most people start at 500 mg. 

Your healthcare provider will determine an appropriate dose. They may choose to start you at a lower amount and gradually increase your dose to reduce the risk of side effects.

Your healthcare coverage, along with any savings programs or coupons, will impact the cost of metformin. Because metformin has been on the market for a long time and is available as a generic, it may still be affordable even if you don’t have insurance coverage. 

Without insurance, metformin can cost between $10 and $30 per month; with insurance or other coupons the price averages from about $5 to $15. Note that these prices may vary by dose and form (oral tablet or oral solution). 

While metformin may support weight loss, the results tend to be modest. 

Newer weight loss medications called glucagon-like-peptide-1 receptor agonists (GLP-1s), such as Zepbound or Wegovy, may promote more significant weight loss results.  

But GLP-1s aren’t miracle drugs, either. Medications like Wegovy and Zepbound must be combined with intensive lifestyle changes, including a reduced-calorie diet and moderate exercise (150 minutes per week), and taken long-term to achieve significant and sustained weight loss. 

While considered safe and effective, GLP-1s may also come with unpleasant side effects. Common side effects include mild to moderate GI symptoms, but more serious health risks or complications may also occur in certain groups of people. 

Lastly, these medications are expensive and can cost more than $1,000 per month without insurance. 

If you’re curious about other treatments for weight loss, talk to your provider. They can help you determine which medications or other alternatives might be best for you based on your health history, goals, and other factors. 

• Research shows that taking metformin only leads to modest weight loss if any at all. 

• However, metformin has several potential health benefits, including blood sugar regulation, boosting insulin sensitivity and cell function, and helping to control appetite—all of which may improve overall health and make it easier for some people to lose weight. 

• Metformin is considered safe but may come with side effects. Certain people should not take metformin due to the increased risk of severe side effects or complications.

• Always talk to a knowledgeable and experienced healthcare provider before beginning any treatments for weight loss. They can help you find safe and sustainable options. 

Metformin won’t make weight magically disappear. But for people with certain conditions, or those on certain medications, who are having difficulty meeting their weight goals through diet and exercise alone, metformin could provide an extra boost. 

If you’re curious about medications to help you lose weight, talk to your healthcare provider about possible safe and effective treatment plans. 

---

How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our 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 writer.

Editorial Guidelines | Medical Review Process

Current version

November 27, 2024

Written by

Jennifer Chesak

Fact checked by

Nesochi Okeke-Igbokwe, MD, MS

---

About the medical reviewer

Nesochi Okeke-Igbokwe, MD, MS

Nesochi Okeke-Igbokwe, MD, MS, is a physician, health expert, media contributor, and health writer based in the New York City area. She’s a practicing internist as well as a civil surgeon designated by the United States Department of Homeland Security and the United States Citizenship and Immigration Services.