Metformin weight loss: does it really work?

If you struggle with weight gain, you’re not alone. Over 73% of adults in the United States over the age of 20 years old have measurements in the overweight or obese range according to BMI. But, losing a healthy amount of weight (as agreed upon with your healthcare provider) and keeping the weight off can be challenging for many–you might be curious about medications like metformin to help you on your weight loss journey. Though metformin wasn’t designed as a weight loss drug, research shows it may help people shed unwanted pounds. 

Metformin is a medication prescribed to treat type 2 diabetes (T2D). Metformin helps lower blood sugar levels in people who cannot meet their goals with diet and exercise alone. The American Diabetes Association (ADA) considers it the preferred first-line diabetes drug for diabetics ten years old and up.

Metformin’s primary purpose is to lower blood glucose (blood sugar) levels. It does this in three ways. First, it reduces glucose production in the liver. Second, it slows down glucose absorption through the intestines. Third, it increases insulin sensitivity to help the body better process glucose.

Metformin may be prescribed off-label for several other purposes. These include gestational diabetes (diabetes diagnosed during pregnancy), type 2 diabetes prevention, and polycystic ovary syndrome (PCOS). Providers also prescribe it to people taking antipsychotic medications to manage the weight gain experienced with those drugs.

Metformin is a safe and effective drug for treating type 2 diabetes, but does metformin help you lose weight? The answer is it may, for some. Metformin is not a replacement for healthy eating and exercise. 

New studies have shown that metformin may have other health benefits, and weight loss is high among them. At first, scientists thought metformin weight loss was a direct result of lowering glucose, but research shows there may be more to the side effect—metformin may lower food intake by reducing appetite. However, exactly how the drug curbs appetite isn’t fully understood.

Early research on metformin was limited to people with diabetes. 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. However, this was still preferable to other drugs that cause weight gain.

An early study of people with diabetes and morbid obesity found significant weight loss after 28 weeks of metformin alongside a healthy diet. Other risk factors for coronary heart disease were lowered as well, including fasting insulin, leptin, and LDL cholesterol. This study was small, however, and contained no placebo group.

Even in studies that indicated weight loss, the results were modest. One of the most extensive studies to date, performed by the Diabetes Prevention Program (DPP), tested metformin in people with prediabetes (those at risk for developing T2D). People randomly assigned metformin lost an average of 4-7 pounds.

Even for groups in which metformin shows clear weight benefits, it isn’t a magic pill by any stretch. The amount of weight reduced appears to level off over time. In the DPP study, 29% of people in the group taking metformin lost 5% or more of their body weight by the end of the first year. At the end of year two, 26% of the group had maintained their weight loss. The average reduction in waist size did not change much between year one and year two, either. However, these results were superior to results of the placebo group. 

The keyword regarding the effectiveness of metformin for weight loss is modest. Metformin can’t replace lifestyle changes like adopting a healthy diet and exercise routine. Weight loss tends to be small and takes time to achieve. But for people with diabetes or prediabetes, metformin may offer an extra boost.

In addition to those with type 2 diabetes, other people may benefit from metformin. Some people taking antipsychotic medications may develop a condition called metabolic syndrome. Weight gain and elevated lipids (triglycerides and cholesterol) are among the many signs of this syndrome. In one study, people on antipsychotics gained an average of eight pounds during the first twelve weeks of treatment. For people new to antipsychotics, those taking metformin saw significantly reduced weight gain, lower body mass index (BMI), and lower insulin resistance.

Metformin is not for everyone. The drug carries a black box warning from the FDA. You should not take metformin if you have severe kidney disease. Metformin may contribute to a condition called lactic acidosis, which can be life-threatening. If you are over 65 and have experienced any of the following, metformin might not be safe for you:

• Heart attack

• Stroke

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

• Liver disease

• Heart disease

• Coma

• Excessive alcohol consumption

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.

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.

When to contact your healthcare provider

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

• Dizziness, lightheadedness

• Extreme tiredness, weakness, or discomfort

• Confusion

• Coma

• Tremors

• Sweating

• Numbness/tingling

• Nausea, vomiting, stomach pain

• Deep, rapid breathing or shortness of breath

• Fast or slow heartbeat

• Flushing of the skin

• Muscle pain

• Feeling cold, especially in your hands or feet

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. If you find yourself drinking less fluid for any reason, talk with your provider.

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

• Diarrhea

• Bloating, gas

• Indigestion, heartburn

• Constipation

• Metallic taste

• Headache

• Changes to the fingernails or toenails

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

Some medications may increase your risk of developing serious side effects if taken with metformin, including: 

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

• Cimetidine (brand name Tagamet)

• Insulin or other medications for diabetes

• Diuretics (water pills)

• Oral steroids such as dexamethasone, methylprednisolone, and prednisone

• Medications for thyroid disease

• Oral contraceptives (birth control pills)

• Hormone replacement therapy

• Calcium channel blockers

• Phenytoin (brand name Dilantin)

• Niacin

• Medications for asthma and colds

Medications not included in these lists may also cause possible interactions. Tell your healthcare provider about all medications, both prescription and over-the-counter, and vitamins or supplements (including herbal supplements) you take before taking metformin.

Metformin is available both generically 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. 

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. 

As with all medication, the cost of metformin will be impacted by your healthcare coverage. If the drug isn’t covered by your insurance, metformin still may be affordable. Cost ranges from about $5 to $14 for a thirty-day supply, depending on the dose.

Unfortunately, metformin won’t magically melt away fat. But for people with certain conditions who are unable to meet their weight goals through diet and exercise alone, it could provide an extra boost. If you want to lose weight, talk to your healthcare provider about possible safe and effective treatment plans for you. 

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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.

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Current version

March 08, 2023

Written by

Seth Gordon

Fact checked by

Chimene Richa, MD

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About the medical reviewer

Chimene Richa, MD

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.