Metformin for Weight Loss: How Much You Lose, With or Without Diabetes

Metformin causes modest weight loss: about 2% of body weight on average, against almost none on placebo, in the main long-term trial of people without diabetes.^[1] It is not FDA-approved for weight loss, so using it this way is off-label.^[4] The weight it takes off is small next to Wegovy or Zepbound, whose pivotal trials reported losses of about 15% and 21%,^[5][6] but a minority of people on metformin lose more and keep it off, and the drug is cheap.

How much weight do people lose on metformin?

The best long-term figures come from the Diabetes Prevention Program, a randomized trial of 3,234 adults with raised blood sugar but no diabetes and an average BMI of 34.^[2] Over the two-year blinded phase, people taking metformin 850 mg twice a day lost 2.06% of their weight, against 0.02% on placebo. In the open follow-up the gap held, at 2.0% against 0.2%, and weight loss tracked with how consistently people took the drug.^[1]

A 2024 meta-analysis pooled 49 randomized trials of people without diabetes who had overweight or obesity, and it reached a similar size of effect. Metformin lowered BMI by 0.56 points compared with placebo, roughly 1.6 kg for someone 5 ft 7 in tall. The authors rated the trials as low quality and found no significant difference between metformin and lifestyle change alone. Orlistat beat it.^[3]

That last row is the number often quoted online, and it deserves the least weight. The 154 patients in that clinic study were not randomized, and the 45 controls were people who declined treatment.^[9][7] The BIGPRO figures come from a 2023 review in the Cleveland Clinic Journal of Medicine.^[7]

An average also hides a split. After one year of the prevention trial, 28.5% of the metformin group had lost at least 5% of their weight. In a post hoc analysis, those people were still 6.2% below their starting weight in years 6 to 15, more than the comparable subgroups from lifestyle (3.7%) and placebo (2.8%).^[8] The early months predict the rest fairly well: most of the loss arrives in the first 6 to 12 months.^[7]

Does metformin cause weight loss if you don't have diabetes?

Yes, and that is the population nearly all of the numbers above describe. The FDA label is a different matter. Metformin is indicated only to improve blood sugar in type 2 diabetes, in adults and children 10 and older. In the label’s own 29-week diabetes trial, the metformin group lost 1.4 lb and the placebo group 2.4 lb.^[4] The drug’s reputation for weight loss therefore comes from trials outside its label.

How it works is unsettled. Proposed mechanisms include lower appetite through gut hormones, changes in the gut microbiome and a rise in GDF-15, a stress hormone that reduces food intake.^[7] A small 2026 trial found that the people whose GDF-15 rose most lost the most weight, and that weight drifted back toward baseline after they stopped the drug.^[10] That trial enrolled 40 older people with HIV, so it is a hint and nothing firmer.

What dose of metformin is used for weight loss?

No dose has been approved for this use, because the use itself is unapproved. The trial that produced the longest data used 850 mg twice a day, or 1,700 mg daily.^[2] The Cleveland Clinic review, which favors off-label use, aims for 1,500 mg a day or more, with slow increases and extended-release tablets. It reports no difference in weight loss between the immediate-release and extended-release forms.^[7] The 2024 meta-analysis found no clear link between dose and effect across a range of 500 to 2,550 mg a day, so a higher dose has not been shown to mean more weight loss.^[3]

The label’s diabetes dosing starts at 500 mg twice a day or 850 mg once a day with meals, and tops out at 2,550 mg a day.^[4] Any dose for weight is a prescriber’s decision. Kidney function sets the limits, as the side-effects section below explains.

Who is most likely to benefit from metformin for weight?

• People with prediabetes. Metformin cut new diabetes by 31% in the prevention trial, while lifestyle change cut it by 58%.^[2] The ADA says metformin should be considered in adults at high risk, especially those aged 25 to 59 with a BMI of 35 or more.^[11] How that compares with a GLP-1 is in GLP-1 drugs for prediabetes.
• People gaining weight on antipsychotics. A 2026 network meta-analysis in JAMA Psychiatry put metformin at −3.86 kg against placebo or standard care across 16 trials, with moderate certainty. Semaglutide (−10.98 kg) and liraglutide (−5.43 kg) did better, on far fewer trials.^[12] A separate meta-analysis of 20 placebo-controlled studies found −3.32 kg.^[13]
• Women with polycystic ovary syndrome. The Cleveland Clinic review lists PCOS among its priority groups.^[7] The trials against newer drugs are covered in GLP-1 drugs for PCOS.
• Children and teenagers: unclear. A 2026 Cochrane review called the metformin evidence against no treatment very uncertain, based on three studies and 151 participants.^[14] In a Spanish trial of 160 children, metformin improved BMI score only in those who had not reached puberty.^[15]

Does metformin work as well as Ozempic for weight?

No. No large trial has put metformin against a weight-loss dose of a GLP-1 in people without diabetes, so the comparison below crosses trials with different people and lengths, and it is a rough guide only. The gap is still wide enough that those differences are unlikely to close it.^[1][5][6] One small three-month study did compare the two directly and is described in our piece on genetic testing for weight-loss drugs; semaglutide won clearly.

Metformin’s case rests on price and track record. The 2023 review put a 90-day supply at about $10,^[7] far below the cash prices in our guide to buying a GLP-1 without insurance. Its long-term data also run past 15 years, though a 2026 analysis of the same trial found that lifestyle change, not metformin, was tied to fewer chronic conditions in later life.^[17] Whether metformin extends life is a separate question, taken up in metformin versus GLP-1 drugs for longevity. Our drug weight-effect lookup places metformin among other non-GLP-1 medicines.

What are the side effects of metformin for weight loss?

The stomach is the main complaint. In the diabetes trial on the label, diarrhea affected 53% of people on metformin against 12% on placebo, and nausea or vomiting 26% against 8%.^[4] In the prevention trial these symptoms were more common on metformin and eased over time, and no significant safety problems emerged over the long follow-up.^[1] Extended-release tablets and taking the dose after meals tend to cause fewer of them.^[7]

Vitamin B12 is the slow-moving risk. In the same trial, low levels were more common on metformin at 5 years (4.3% against 2.3%), though no longer significantly so at 13 years (7.4% against 5.4%). Low or borderline-low levels were more common at both points, reaching 20.3% against 15.6%.^[16] The label calls for a B12 test at intervals of 2 to 3 years.^[4]

The rare serious hazard is lactic acidosis, which carries a boxed warning. Metformin must not be used with an eGFR below 30. The label’s risk factors also include age 65 or older, heavy drinking, liver impairment, surgery and contrast scans. It also names topiramate, one half of the weight-loss drug Qsymia.^[4] Someone with reduced kidney function who wants to use metformin for weight should expect their prescriber to lower the dose or rule it out.^[7]

Should you take metformin to lose weight?

It suits a narrow set of people: someone with prediabetes or an antipsychotic-related gain who wants a cheap, long-studied drug and would be satisfied with a few percent of body weight. The Cleveland Clinic review argues it should be seriously considered off-label, particularly in those groups, and that is expert opinion resting on the trials above.^[7] Someone hoping for 10% or more is unlikely to reach it on metformin alone. The realistic test is the first year. People who had lost at least 5% by then were the ones who stayed down.^[8]