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Last updated: Mar 10, 2021
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Metformin for weight loss: does it really work?

steve silvestro

Medically Reviewed by Steve Silvestro, MD

Written by Seth Gordon


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

Losing weight is no easy feat, especially if you’ve got more than just a few pounds to shed. And if you’re feeling frustrated, you’ve probably looked into all sorts of options for help. You might have heard about metformin weight loss, but is that a real side effect you can expect from this diabetes medication? Let’s take a look.


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What is metformin?

Metformin is a medication prescribed to people with type 2 diabetes (T2D). Metformin helps lower blood sugar levels in people who cannot meet their goals with diet and exercise. The American Diabetes Association (ADA) considers it the top first-line diabetes drug for diabetics ten years old and up (Corcoran, 2020).

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 (Corcoran, 2020).

You’ve probably heard that metformin may help some people lose weight as well. Does it? The answer is: possibly, a little bit, for some. It’s not a replacement for healthy eating and exercise. We’ll look at some of the mechanisms of metformin and who might benefit from it.

Metformin for weight loss

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 (Corcoran, 2020).

New studies have shown that metformin may have other health benefits, weight loss high among them. At first, scientists thought metformin weight loss was a direct result of lowering glucose. But research has indicated there may be more going on. Studies suggest that metformin may lower food intake by reducing appetite. However, the exact ways it does this aren’t fully understood yet (Yerevanian, 2019).

Early research on metformin was limited to people with diabetes and found small benefits for weight with people taking metformin versus placebo, sulfonylurea, or other diabetes medications. Other studies found metformin treatment to only be “weight neutral,” meaning that people neither gained nor lost weight while taking it. However, this was still preferable to other drugs that stimulated weight gain (Golay, 2008).

An early study on 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 (Glueck, 2001).

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 4.6 pounds (Yerevanian, 2019).

There are other people for whom metformin may be beneficial. Many people taking antipsychotic medications are known to develop a condition called metabolic syndrome. Weight gain and elevated lipids (triglycerides and cholesterol) are among the many signs of metabolic syndrome. In one study, people on antipsychotics gained on average 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 (de Silva, 2016).

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. When checking at 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 reductions were both superior to those for the placebo group (DPP, 2012). 

The word one reads over and over again in studies on the effectiveness of metformin treatment for weight loss is modest. It can’t replace important lifestyle changes around diet and exercise. Losses tend to be small and can take some time to achieve. Lifestyle changes, such as dieting and exercise, remain the best methods for losing weight. But for people with diabetes or prediabetes, metformin may offer an extra boost.

Metformin precautions

Metformin carries a black box warning from the FDA. Metformin may contribute to a condition called lactic acidosis, which can be life-threatening. Some medical conditions are risk factors for this problem. Be sure to tell your healthcare provider if you have or have ever had any of the following conditions (MedlinePlus, n.d.):

  • kidney disease
  • heart attack, or any heart disease
  • stroke
  • diabetic ketoacidosis
  • liver disease
  • coma

If you drink alcohol, be honest about your drinking habits, including binge drinking. Alcohol increases the risk of lactic acidosis.

When to contact your healthcare provider

If you experience symptoms of lactic acidosis when taking metformin, contact your healthcare provider immediately. Symptoms include:

  • extreme tiredness, weakness, or discomfort
  • nausea, vomiting
  • stomach pain
  • decreased appetite
  • deep, rapid breathing
  • shortness of breath
  • dizziness, lightheadedness
  • 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 (MedlinePlus, n.d.).

If you have any type of surgical procedure (including dental), or any x-ray procedure with dye injection, inform someone you are taking metformin.

Tell your prescriber if you are pregnant or plan to become pregnant before taking metformin. If you become pregnant when taking it, inform them as soon as possible, and follow their medical advice.

Side effects of metformin

Metformin is generally well-tolerated, but adverse effects can happen. In addition to the symptoms outlined above under precautions, tell your healthcare provider if you experience any of the following when taking metformin (MedlinePlus, n.d.):

  • 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, get emergency treatment. It could be a sign of an allergic reaction or another serious issue.

Drug interactions

In addition to drugs mentioned above under Precautions, some medications may interact or affect your ability to take metformin. Be sure to mention if you are taking any of the following medications (and always share your full list of medications with your healthcare provider) (MedlinePlus, n.d.):

  • angiotensin-converting enzyme (ACE) inhibitors
  • beta-blockers
  • calcium channel blockers
  • diuretics (‘water pills’)
  • hormone replacement therapy
  • insulin or other medications for diabetes
  • medications for asthma and colds
  • medications for mental illness and nausea
  • medications for thyroid disease
  • morphine
  • niacin
  • oral contraceptives (birth control pills)
  • oral steroids such as dexamethasone, methylprednisolone, and prednisone

Certain medications may also increase the risk of lactic acidosis as described above. It’s important to tell your provider if you are taking any of the following (MedlinePlus, n.d.):

  • acetazolamide (brand name Diamox)
  • dichlorphenamide (brand name Keveyis)
  • methazolamide
  • topiramate (brand name Topamax, also a component of Qsymia)
  • zonisamide (brand name Zonegran)

These are not complete lists of all possible interactions. Tell your healthcare provider about all medications, both prescription and over-the-counter, and vitamins or supplements (including herbal supplements) you are taking before taking metformin.

Dosage and cost

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 taper up. 

If not covered by your insurance, metformin is inexpensive. The cost ranges from about $5 to $14 for a thirty-day supply, depending on the dose (GoodRx).

Speak with your healthcare provider

Metformin won’t melt away the fat. But for people with certain conditions who aren’t meeting weight goals through healthy habits like exercise and diet, it could provide that extra bit of help needed. If you need to lose weight, talk to your healthcare provider about solutions that might work for you. 


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  2. de Silva, V. A., Suraweera, C., Ratnatunga, S. S., Dayabandara, M., Wanniarachchi, N., & Hanwella, R. (2016). Metformin in prevention and treatment of antipsychotic induced weight gain: A systematic review and meta-analysis. BMC Psychiatry, 16(1), 341. doi: 10.1186/s12888-016-1049-5. Retrieved from https://pubmed.ncbi.nlm.nih.gov/27716110/
  3. Diabetes Prevention Program Research Group. (2012). Long-term safety, tolerability, and weight loss associated with metformin in the Diabetes Prevention Program Outcomes Study. Diabetes Care, 35(4), 731–737. doi: 10.2337/dc11-1299. Retrieved from https://pubmed.ncbi.nlm.nih.gov/22442396/
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  5. Glueck, C. J., Fontaine, R. N., Wang, P., Subbiah, M. T., Weber, K., Illig, E., et al. (2001). Metformin reduces weight, centripetal obesity, insulin, leptin, and low-density lipoprotein cholesterol in nondiabetic, morbidly obese subjects with body mass index greater than 30. Metabolism: Clinical and Experimental, 50(7), 856–861. doi: 10.1053/meta.2001.24192. Retrieved from https://pubmed.ncbi.nlm.nih.gov/11436194/
  6. Golay, A. (2008). Metformin and body weight. International Journal of Obesity (2005), 32(1), 61–72. doi: 10.1038/sj.ijo.0803695 Retrieved from https://pubmed.ncbi.nlm.nih.gov/17653063/
  7. GoodRX (n.d.) Metformin. Generated interactively: Retrieved February 19, 2021, from https://www.goodrx.com/metformin
  8. MedlinePlus (n.d.). Metformin: Medlineplus drug information. Retrieved February 19, 2021, from https://medlineplus.gov/druginfo/meds/a696005.html
  9. Yerevanian, A., & Soukas, A. A. (2019). Metformin: Mechanisms in human obesity and weight loss. Current Obesity Reports, 8(2), 156–164. doi: 10.1007/s13679-019-00335-3. Retrieved from https://pubmed.ncbi.nlm.nih.gov/30874963/

Dr. Steve Silvestro is a board-certified pediatrician and Manager, Medical Content & Education at Ro.