Does Metformin Cause Weight Gain or Weight Loss?

Metformin is a prescription oral medication primarily used as a therapy for type 2 diabetes, a condition characterized by elevated amounts of blood glucose (a.k.a. sugar).

What's lesser known is that it's one of the few diabetes drugs that's not associated with weight gain, per the Mayo Clinic.

And while this drug has mechanisms that can promote modest weight loss, the use of metformin does not guarantee results. If you have diabetes, or if you have questions on the risks and benefits of using metformin, talk with your doctor.

Metformin has been used in the U.S. since 1995 and is one of the most widely prescribed diabetes medications — often the first choice when diabetes pills are indicated, per Yale School of Medicine. It lowers blood glucose by reducing the amount of sugar the liver sends into the bloodstream. Metformin also improves the body's response to insulin, a hormone that not only helps the body use sugar but also keeps blood sugar from getting too high.

While the U.S. Food and Drug Administration (FDA) has approved the use of metformin for the treatment of type 2 diabetes, this medication is also used off-label (without formal FDA approval), in the management of other conditions, such as prediabetes, polycystic ovary syndrome (PCOS) and in the treatment of obesity.

Metformin has the potential to cause weight loss via several mechanisms, with appetite control at center stage, per an October 2014 review in ‌Current Opinion in Endocrinology, Diabetes & Obesity‌.

Metformin improves the body's response to the hormones insulin and leptin, which in turn decreases appetite, and also causes a cascade of reactions in the central nervous system that work to reduce hunger, according to the above review.

Additionally, this medication works in the gut to positively affect gut bacteria and raise glucagon-like peptide-1 (GLP-1) hormone levels, increasing the sense of fullness. Metformin also reduces fat deposits in the liver and muscles, which can lead to weight loss, per the review.

However, not all weight loss while on metformin can be attributed to the drug. For instance, metformin is often prescribed shortly after a diabetes diagnosis, a time when other weight-loss strategies — such as improved diet and increased exercise — are employed. In addition, some people respond to nausea and diarrhea — common metformin side effects — by eating less, per a January 2019 review in ‌Diabetes Care‌.

Finally, metformin does not increase the risk of hypoglycemia, or low blood sugars. Because hypoglycemia prevention and treatment involves snacking more and drinking juice or soda when your blood sugar gets too low, people using metformin as their only diabetes drug aren't prompted to eat these extra calories, per the ‌Diabetes Care‌ review.

Metformin is being studied and sometimes prescribed for the treatment of obesity, even in people who don't have diabetes. While this medication can promote weight loss, weight reduction is not as much as some people need or desire to lose in order to improve health, per a June 2017 report in ‌Diabetes, Metabolic Syndrome and Obesity‌.

However, metformin may be a helpful adjunct in the treatment of obesity, which means that it works along with efforts to improve food choices, reduce calorie intake and increase physical activity, per the report.

Metformin may also help promote weight loss in those who gain weight from psychotropic medications (i.e., antipsychotics), including risperiodone, quetiapine and more, per an August 2017 study in ‌Neuropsychiatric Disease and Treatment‌.

Weight loss is not guaranteed when taking metformin. A small 2013 study in ‌Experimental and Clinical Endocrinology and Diabetes‌ of people who had obesity but did not have diabetes showed that while the majority of study participants lost five percent of their weight after six months of metformin treatment, 20 percent didn't lose any weight.

Reasons for this vary, but seem related to body weight or diet before treatment, lifestyle efforts during treatment and/or the effects of other medications. For instance, some people have overweight or may have already lost weight before starting metformin and may not lose additional pounds after starting this medication.

Others might not feel a reduced appetite or gastrointestinal side effects, and so are not prompted to eat less. Also, when metformin is combined with other diabetes drugs that could promote modest weight gain, such as insulin, the weight-loss benefits of metformin may not be realized, per the Mayo Clinic.

Metformin is a prescription drug most commonly used to treat diabetes. Side effects include diarrhea, cramping and nausea, but most people report these symptoms go away after a week or two, per the U.K.'s National Health Service.

Serious side effects could happen if metformin is used in people with severe kidney disease or in people who abuse alcohol while using this drug, so talk to your doctor about risks, dosing and safety issues while taking this medication.

If you get gastrointestinal side effects that do not go away, let your doctor know. If you want help losing weight, talk to your doctor and ask for a referral to a dietitian or a weight management program.