Metformin for weight loss: how much people lose in trials

Metformin can lead to a small amount of weight loss, but it isn’t approved for it and the average effect is modest. In the best-known trial, the Diabetes Prevention Program, adults with prediabetes lost about 2.1 kg (4.6 lb) on metformin over roughly 3 years, compared with 0.1 kg on placebo and 5.6 kg with an intensive lifestyle program.

That makes metformin very different from the GLP-1 drugs approved for weight loss: Wegovy 2.4 mg, for example, produced an average loss of 14.9% of body weight in its main trial. This guide covers what the metformin trials found, who gets it prescribed, and how it compares with Ozempic and Wegovy.

Is metformin approved for weight loss?

No. The metformin label approves it, with diet and exercise, to improve blood sugar control in adults and children 10 and older with type 2 diabetes. Prescribing it for weight loss, or for people without diabetes, is off-label. That’s legal, but it means the FDA hasn’t reviewed whether metformin works for that purpose.

The label describes how metformin lowers blood sugar: it reduces the amount of glucose the liver makes, reduces how much glucose the gut absorbs, and makes the body more sensitive to insulin. It doesn’t list weight loss as an effect.

How much weight people lose on metformin

The best evidence comes from the Diabetes Prevention Program (DPP), a US trial of 3,234 adults with prediabetes. Their average body mass index was 34 and their average weight about 94 kg (207 lb). They were randomly assigned to placebo, metformin 850 mg twice a day, or an intensive lifestyle program aiming for 7% weight loss and 150 minutes of activity a week, and followed for an average of 2.8 years.

Metformin cut new cases of type 2 diabetes by 31% compared with placebo. The lifestyle program cut them by 58% and produced more than twice the weight loss.

Does the weight stay off?

The DPP participants were followed for years afterward in the DPP Outcomes Study. During the original 2-year blinded phase, people on metformin lost 2.06% of their body weight on average vs 0.02% on placebo. During the open-label years that followed, the difference held: 2.0% on metformin vs 0.2% on placebo. The authors concluded the weight loss was durable for at least 10 years of treatment.

How much a person lost depended on whether they took the pills:

• People in the most adherent group, based on pill counts, were 3.5% below their starting weight at 2 years, close to what they had lost by year 1. Over the whole follow-up, they averaged 3.5% (3.1 kg) below baseline.
• People with low adherence were back at their starting weight by year 2.
• Placebo groups stayed within about 1% of their starting weight.

What happens in people with type 2 diabetes

In type 2 diabetes, metformin is best described as weight-neutral. In the label’s 29-week trial of people with type 2 diabetes and obesity (about 201 to 206 lb at the start), weight fell 1.4 lb on metformin and 2.4 lb on placebo. The older Glucophage label puts it this way: in contrast to sulfonylureas, body weight on metformin “tended to remain stable or even decrease somewhat.”

That is one reason metformin is a common first diabetes drug. It isn’t evidence that it’s a weight-loss drug.

Who gets metformin prescribed

Metformin’s approved use is type 2 diabetes. Beyond that, the American Diabetes Association’s 2026 standards say metformin should be considered to prevent type 2 diabetes in adults at high risk, especially:

• Adults aged 25 to 59 with a BMI of 35 or more
• People with a fasting glucose of 110 mg/dL or higher, or an A1C of 6.0% or higher
• Women who have had gestational diabetes

The same standards note that metformin was less effective than lifestyle change in the DPP overall, but as effective in participants with a BMI of 35 or more and in those aged 25 to 44. Using metformin to prevent diabetes is off-label, because the label covers treatment of type 2 diabetes only.

Some clinicians also prescribe it off-label for weight, and online longevity clinics prescribe it for healthy aging, which we cover in metformin for longevity.

Metformin vs Ozempic and Wegovy

Ozempic and Wegovy are both semaglutide, a GLP-1 receptor agonist given as a weekly injection. Ozempic is approved for type 2 diabetes; Wegovy is the version approved for weight loss. Metformin is a daily pill that works a different way.

Scroll sideways to see the full table

Sources: metformin label and DPP; Ozempic label; Wegovy label. These are different trials in different people, so the numbers show scale rather than a head-to-head result. In Wegovy’s trial in people with type 2 diabetes, weight fell 9.6% vs 3.4% on placebo, less than in people without diabetes.

The two drugs are often used together in type 2 diabetes. Ozempic was studied added to metformin, and its label says no metformin dose change is needed.

Side effects to expect

Metformin’s most common side effects are in the gut. In the label’s immediate-release trial, 53% of people had diarrhea (12% on placebo) and 26% had nausea or vomiting (8%). The label also carries a boxed warning for lactic acidosis, which is rare, and metformin can lower vitamin B12 over time. Our metformin side effects guide goes through each one, including how the extended-release tablet compares.

What it costs

Metformin is a low-cost generic. As of October 2026, AgelessRx and Hone Health list it at $25 a month and Healthspan at $30 a month on their own sites. Hone Health also requires a membership of at least $25 a month. See the metformin page and our longevity clinic rankings.

GLP-1 treatment costs more. As of November 2026, compounded semaglutide costs $65 to $299 a month at the 20 of the 26 weight-loss programs we rank that publish a price. Compounded semaglutide is not Wegovy or Ozempic and isn’t FDA-approved; a compounding pharmacy prepares it. Our GLP-1 program rankings and cheapest GLP-1 list compare prices, and the weight loss hub covers the approved options.

Questions to ask a prescriber

• Is metformin meant to treat a condition I have, such as prediabetes, or only for weight?
• How much weight is realistic for me, given the trial averages?
• Would immediate-release or extended-release suit me better?
• Will you check my kidney function before I start and my B12 over time?
• If weight is the main goal, would an approved weight-loss medicine fit me better?

The bottom line

Metformin is a cheap, well-studied diabetes drug, and in people with prediabetes it produced a small, lasting weight loss: about 2 kg on average, and about 3.5% of body weight in people who took it consistently. Weight loss is an off-label use, and the amount is a fraction of what the GLP-1s approved for weight loss produced in their trials. Metformin makes most sense when there’s another reason to take it, such as prediabetes, and a clinician can tell you whether that applies. For other routes, see our guide to Ozempic alternatives and how berberine compares with metformin.