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Metformin for Weight Loss: How Much Can You Really Lose vs GLP-1s?

Metformin produced an average 2.1 kg weight loss in the Diabetes Prevention Program, where body weight fell 2.06% with metformin vs 0.02% with placebo. Wegovy (semaglutide) delivered 13.7% and Zepbound (tirzepatide, a dual GIP/GLP-1) 20.2% at 72 weeks. Metformin is not FDA-approved for weight loss.

Last checked September 14, 2026·10 sources cited·Ozempic

Balance scale comparing a small tablet against an injection pen, with a bathroom scale nearby

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Metformin produces a small amount of weight loss. In the Diabetes Prevention Program (DPP), a randomized double-blind trial in people with prediabetes, participants taking metformin lost an average of 2.1 kg, and body weight fell by 2.06% ± 5.65% with metformin versus 0.02% ± 5.52% with placebo (P < 0.001) ^[4]. That is a fraction of what the newer injectable medications deliver. In the 72-week SURMOUNT-5 trial, people taking Zepbound (tirzepatide, a dual GIP and GLP-1 receptor agonist) lost an average of 20.2% of body weight, or 22.8 kg (50.3 lb), while people taking Wegovy (semaglutide, a GLP-1 receptor agonist) lost an average of 13.7%, or 15.0 kg (33.1 lb) ^[6]. Metformin is also not FDA-approved for weight loss; it is indicated only for diabetes management ^[4].

The comparison is not really close on weight alone. But metformin has a different strength: in the DPP, it reduced the development of type 2 diabetes by 31% over an average of 2.8 years, and the weight people lost on it tended to hold for at least 10 years of continued treatment ^[4]. Here is how the numbers stack up and what they mean for different goals.

What is metformin, and why do people use it for weight?

Metformin is a biguanide-class drug. It was first synthesized in 1922, approved for diabetes treatment in Europe in the 1950s, and approved by the FDA in the United States in 1994 ^[2]. It works in part by activating AMP-activated protein kinase (AMPK), and it is a first-line drug for type 2 diabetes ^[2]. The United Kingdom Prospective Diabetes Study (UKPDS) found it was the only oral antihyperglycemic agent shown to reduce macrovascular complications in people with type 2 diabetes ^[2].

Two related biguanides, phenformin and buformin, were abandoned in the 1970s because of a high frequency of lactic acidosis and increased mortality ^[2].

Metformin gets attention for weight because, unlike many antidiabetic drugs that are associated with weight stability or gain, it is associated with weight loss when used to treat diabetes ^[4]. That association is real but modest, and using it specifically for weight loss is off-label — the drug is indicated only for diabetes management, not for weight loss in people with or without diabetes ^[4].

How much weight can you lose on metformin?

The clearest numbers come from the Diabetes Prevention Program, a randomized double-blind trial that enrolled 3,234 participants at 27 U.S. clinics between 1996 and 1999 ^[4]^[3]. The analysis of metformin versus placebo covered 2,155 participants: 1,073 on metformin and 1,082 on placebo ^[4].

Participants were at least 25 years old with a BMI of 24 kg/m² or higher (22 or higher in Asian Americans), fasting glucose of 95–125 mg/dL, and impaired glucose tolerance of 140–199 mg/dL two hours after a 75-g oral glucose load — in other words, people with prediabetes, not a general weight-loss population ^[4].

In the trial protocol, metformin was started at 850 mg once daily and increased by one month to 850 mg twice daily unless gastrointestinal symptoms required a slower titration — this was the study’s design, not a recommended dose ^[4].

The results:

During the randomized double-blind phase, metformin participants lost an average of 2.1 kg ^[4].
Body weight fell by 2.06% ± 5.65% with metformin versus 0.02% ± 5.52% with placebo (P < 0.001) ^[4].
Waist circumference fell by 2.13 ± 7.06 cm with metformin versus 0.79 ± 6.54 cm with placebo (P < 0.001) ^[4].
In a post hoc analysis, the magnitude of weight loss during the two-year double-blind period was directly related to how adherent people were to the drug (P < 0.001) ^[4].

The first phase of the DPP ended in 2001 after an average of 3.2 years of follow-up, on the advice of the Data and Safety Monitoring Board, because the lifestyle and metformin interventions were so effective at preventing diabetes ^[4].

Does the weight stay off if you keep taking metformin?

It can, according to the long-term follow-up. After the blinded phase ended, participants were unblinded and invited into the DPP Outcomes Study (DPPOS), a 7–8 year open-label extension; 88% of DPP participants joined ^[4].

Throughout the unblinded follow-up, weight loss remained significantly greater in the metformin group than the placebo group: 2.0% versus 0.2% (P < 0.001), and this was related to the degree of continued metformin adherence ^[4]. Across the combined DPP plus DPPOS period, metformin participants maintained an average 2.5-kg weight loss over time ^[4]. The authors concluded that weight loss related to metformin adherence is durable for at least 10 years of treatment ^[4].

A separate analysis looked at who kept weight off longest. Of the 3,234 randomized participants, 1,066 lost at least 5% of their baseline weight in year 1 and were followed for 15 years ^[3]. In year 1, 28.5% of metformin participants (289 people), 62.6% of intensive lifestyle participants (640), and 13.4% of placebo participants (137) hit that 5% mark ^[3].

Among those year-1 responders, the average weight loss maintained between years 6 and 15 was 6.2% (95% CI 5.2–7.2) for the metformin group, 3.7% (3.1–4.4) for the lifestyle group, and 2.8% (1.3–4.4) for the placebo group ^[3]. Predictors of keeping the weight off included a bigger first-year loss in all groups, and older age plus continued metformin use in the metformin group ^[3].

One important caveat: this was a post-hoc analysis of nonrandomized subsets after year 1, so it is observational rather than a head-to-head comparison ^[3].

Metformin vs Wegovy and Zepbound: how big is the difference?

The most direct GLP-1 comparison comes from SURMOUNT-5, a 72-week, open-label, manufacturer-sponsored Phase 3b trial that randomized 751 adults with obesity, or overweight with at least one comorbidity such as hypertension, dyslipidemia, obstructive sleep apnea, or cardiovascular disease, and without diabetes, at sites in the U.S. and Puerto Rico ^[6]. Participants were assigned to a maximum tolerated dose of tirzepatide (10 mg or 15 mg) or semaglutide (1.7 mg or 2.4 mg), along with counseling on a reduced-calorie diet and increased physical activity ^[6].

At 72 weeks, tirzepatide produced an average weight reduction of 20.2% (22.8 kg, or 50.3 lb) versus 13.7% (15.0 kg, or 33.1 lb) for semaglutide — a 47% greater relative weight loss for tirzepatide ^[6].

Medication	Average weight loss	Study	Source
Metformin	2.1 kg average loss in the metformin arm; body weight fell 2.06% vs 0.02% with placebo	DPP randomized phase	^[4]
Wegovy (semaglutide)	13.7% (15.0 kg / 33.1 lb) at 72 weeks	SURMOUNT-5	^[6]
Zepbound (tirzepatide)	20.2% (22.8 kg / 50.3 lb) at 72 weeks	SURMOUNT-5	^[6]

The share of people hitting major weight-loss milestones also differs sharply. In SURMOUNT-5, 81.6% of tirzepatide participants lost at least 10% of body weight versus 60.5% on semaglutide; 64.6% lost at least 15% versus 40.1%; 48.4% lost at least 20% versus 27.3%; and 31.6% lost at least 25% versus 16.1% ^[6]. Waist circumference fell by an average of 18.4 cm (7.2 in) with tirzepatide versus 13.0 cm (5.1 in) with semaglutide ^[6].

A physician commentary from NewYork-Presbyterian/Weill Cornell Medicine’s Comprehensive Weight Control Center describes the drug class in similar terms: semaglutide yields average weight loss of about 15%, with roughly a third of people losing 20%, while tirzepatide pushes average loss to about 21%, with over a third of patients losing 25% or more ^[1].

Where does Ozempic fit in? Semaglutide is commercialized as Wegovy for people living with obesity and as Ozempic for people with type 2 diabetes — the same drug under different brand names for different indications ^[6]. The semaglutide arm in SURMOUNT-5 used Wegovy, so the 13.7% figure applies to the obesity-labeled product ^[6].

These figures come from different trials in different populations, so they are not a true head-to-head test of metformin against the GLP-1s. But the direction and the size of the gap are consistent across everything published here.

How does metformin compare with other FDA-approved obesity drugs?

Even against older obesity medications, metformin’s effect is small. A JAMA systematic review found that obesity medications approved for long-term use, prescribed with lifestyle intervention, produced additional weight loss relative to placebo of roughly 3% of initial weight for orlistat and lorcaserin, up to 9% for top-dose (15/92 mg) phentermine/topiramate-ER at one year ^[7]. The share of patients achieving at least 5% weight loss ranged from 37–47% for lorcaserin, 35–73% for orlistat, and 67–70% for top-dose phentermine/topiramate-ER ^[7].

Older agents — the combination drugs phentermine/topiramate and naltrexone/bupropion, and the single-agent GLP-1 receptor agonist liraglutide — are associated with potential weight loss of 5% to 10% of body weight ^[1].

A 5% loss is generally considered the threshold for clinically meaningful weight loss, though improvements in some cardiovascular risk factors can appear with sustained losses as small as 3% ^[7]. That review also advised that clinicians can discontinue an obesity medication in patients who do not achieve at least 5% weight loss, to limit exposure to risks and costs when there is little prospect of long-term benefit ^[7]. As of that 2014 review, no obesity medication had been shown to reduce cardiovascular morbidity or mortality ^[7].

For current prescribing guidance, the American Diabetes Association publishes Standards of Care covering the pharmacologic treatment of overweight and obesity; a 2026 edition is available ^[8]^[9].

Does metformin actually prevent diabetes?

This is where metformin’s evidence is strongest. In the DPP, metformin reduced the development of diabetes by 31% over an average of 2.8 years of follow-up ^[4]. Weight loss accounted for 64% of the metformin-versus-placebo effect on diabetes prevention ^[4]. At a median of 10 years since randomization, both the lifestyle and metformin groups had significantly less diabetes than the placebo group ^[4].

So the strongest published case for metformin in people with prediabetes is diabetes prevention, with weight loss as a secondary effect — not the reverse.

What side effects does metformin have, and do they fade?

Metformin’s most common side effects are gastrointestinal. The DPP/DPPOS report describes them as generally transient, resolving spontaneously, and often avoidable through gradual escalation of dosage — a clinical observation from the trial literature, not a dosing instruction for any individual ^[4]. Across the study as reported, gastrointestinal symptoms were more common with metformin than placebo and declined over time, and no significant safety issues were identified ^[4].

A few other points from the study:

During the DPP, hemoglobin and hematocrit were slightly lower in the metformin group than the placebo group; the decrease occurred in the first year after randomization, with no further change observed over time ^[4].
In U.S. clinical trials of metformin generally, about 4% of participants were unable to continue the drug due to adverse effects ^[4].
Serious adverse events are infrequent and generally limited to lactic acidosis, which occurs only in people with renal or hepatic insufficiency or other contraindications ^[4].
Metformin has not been associated with hypoglycemia unless combined with other glucose-lowering medicines such as sulfonylureas or insulin ^[4].

The study’s conclusion was that metformin used for diabetes prevention is safe and well tolerated ^[4].

For comparison, in SURMOUNT-5, 6.1% of tirzepatide participants and 8.0% of semaglutide participants discontinued treatment due to adverse events, which were mainly gastrointestinal and generally mild to moderate — though the study was not powered to compare safety between the two drugs ^[6]. Zepbound also carries a warning about thyroid C-cell tumors and medullary thyroid carcinoma, and is contraindicated in people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 ^[6].

Is berberine an alternative to metformin?

Berberine is an alkaloid extracted from Berberis vulgaris, historically used for diarrhea and dysentery, and used as a non-prescription agent in some countries ^[2]. Studies show berberine exerts hypoglycemic actions similar to metformin, though it has not been extensively used for diabetes treatment ^[2]. Its lipid-lowering effect has been reported as comparable to conventional lipid drugs with low toxicity ^[2].

Both drugs have been studied as candidates in type 2 diabetes, obesity, cardiac disease, tumor, and inflammation — but the evidence base for berberine is largely experimental and early clinical work ^[2].

Who is metformin a good fit for — and who is it not?

Metformin’s best-supported use in this evidence is prediabetes and diabetes prevention, where the endpoint is diabetes incidence rather than pounds ^[4]. If the goal is a 10–15% or greater weight reduction, metformin’s roughly 2% effect does not reach that bar, while the GLP-1 and GIP/GLP-1 agents do ^[4]^[6].

That said, the newer anti-obesity medications have real-world barriers: high cost, insurance coverage exclusions, and lack of treatment persistence ^[1]. There is also a knowledge gap — most obesity drug trials run one year, some two, and long-term outcomes in the literature have generally been reported only at 12–18 months ^[1].

Can you take metformin with a GLP-1, or switch to it after stopping one?

Metformin is a first-line drug for type 2 diabetes ^[2], and GLP-1 receptor agonists were originally developed to treat diabetes mellitus ^[1]. One specific rule from the Zepbound label: it should not be used with other tirzepatide-containing products or any GLP-1 receptor agonist medicine ^[6].

Beyond that, no trial data on metformin added to, or sequenced after, an anti-obesity medication for weight loss has been published in the sources here, so there is no evidence to describe for that approach.

Sources

Frequently asked questions

How many pounds can you realistically lose on metformin?

In the Diabetes Prevention Program, metformin participants lost an average of 2.1 kg during the randomized phase; body weight fell 2.06% with metformin versus 0.02% with placebo. Across the combined DPP and DPPOS follow-up, the average maintained loss was 2.5 kg over time. Individual results vary, and no figure here predicts any one person's outcome.

Is metformin FDA-approved for weight loss?

No. Metformin is indicated only for diabetes management, not for weight loss in people with or without diabetes. Any use of metformin specifically for weight loss is off-label. The DPP report describes it as an established diabetes treatment with a good safety profile, and a first-line drug for type 2 diabetes.

Does the weight come back after stopping metformin?

The published data do not directly answer this. What is known is that continued metformin use was a predictor of maintaining long-term weight loss in the DPPOS analysis, and weight loss during treatment was directly related to adherence. There is no trial data in these sources on what happens after stopping.

How long does metformin weight loss last if you keep taking it?

The DPP/DPPOS authors concluded that metformin-related weight loss is durable for at least 10 years of treatment. Among the subset who lost at least 5% in year 1, the metformin group maintained an average 6.2% loss between years 6 and 15 — though that figure comes from a post-hoc analysis of nonrandomized subsets.

How big is the difference between metformin and Ozempic or Wegovy (semaglutide)?

Metformin participants lost an average of 2.1 kg in the DPP, with body weight falling 2.06% versus 0.02% on placebo. Semaglutide produced an average 13.7% loss (15.0 kg, or 33.1 lb) at 72 weeks in SURMOUNT-5, using Wegovy, the obesity-labeled form of the drug. The two figures come from different trials and populations, so they are not a head-to-head comparison.

How big is the difference between metformin and Zepbound (tirzepatide)?

Metformin participants lost an average of 2.1 kg in the DPP, with body weight falling 2.06% versus 0.02% on placebo. Tirzepatide produced an average 20.2% loss (22.8 kg, or 50.3 lb) at 72 weeks in SURMOUNT-5, with 64.6% of participants losing at least 15% of body weight. Again, these are separate trials, not a head-to-head comparison.

Does metformin prevent diabetes if you have prediabetes?

Yes, this is its strongest evidence. In the DPP, metformin reduced the development of diabetes by 31% over an average of 2.8 years, and at a median of 10 years since randomization, the metformin group still had significantly less diabetes than placebo. Weight loss accounted for 64% of the metformin effect.

What side effects should you expect starting metformin, and do they fade?

The most common side effects are gastrointestinal. The DPP report describes them as generally transient and resolving on their own. Across the study as reported, GI symptoms declined over time and no significant safety issues were identified. In U.S. clinical trials of metformin generally, about 4% of participants could not continue the drug due to adverse effects.

This article summarizes FDA labeling, published research and company information current as of September 14, 2026. It is not medical advice and does not replace a conversation with your own healthcare provider. How we research and verify.