Quick Answer: Metformin can cause modest weight loss, typically about 2 kg (4-5 pounds), or roughly 2-3% of body weight, though some people lose more. In the large Diabetes Prevention Program, about 3 in 10 people on metformin lost at least 5% of their weight in the first year, and those who did kept much of it off for years. Metformin is approved for type 2 diabetes, not weight loss, so using it for weight loss is off-label. It produces far less weight loss than GLP-1 medications like Wegovy or Zepbound, but it's inexpensive, taken by mouth and has decades of safety data.
Educational information only. This is not medical advice. Never start, stop or change a prescription without your prescriber.
What Is Metformin?
Metformin is a pill in the biguanide class and the most widely used first-line medication for type 2 diabetes. It lowers blood sugar mainly by reducing how much glucose the liver releases and by helping the body respond better to insulin.1 It has been used for more than 60 years worldwide and in the US since 1995.
Metformin is FDA-approved for type 2 diabetes. Doctors also commonly prescribe it off-label for:
- Prediabetes, to lower the risk of developing type 2 diabetes, especially in younger adults with a higher BMI2
- Polycystic ovary syndrome (PCOS)
- Weight gain caused by antipsychotic medications3
- Weight management in people with obesity, usually alongside other treatment3
How Much Weight Can You Lose on Metformin?
The best long-term data come from the Diabetes Prevention Program (DPP), which followed 3,234 adults with prediabetes:2,3,4
- Average loss: 2.1 kg (about 4.6 pounds) on metformin over about 2.8 years, compared with 0.1 kg on placebo and 5.6 kg with an intensive diet-and-exercise program.
- Responders: about 30% of people on metformin lost at least 5% of their body weight in the first year.
- Staying power: among people who lost at least 5% in the first year, those on metformin were still an average of 6.2% below their starting weight 6 to 15 years later, compared with 3.7% for those in the lifestyle program.
In smaller trials in people with obesity but without diabetes, weight loss has been similar: around 2 kg more than placebo over a year.3 The takeaway: metformin doesn't produce dramatic weight loss on average, but a meaningful minority of people respond well, and those who do tend to keep it off.
How Metformin Helps With Weight
The exact mechanism isn't fully understood. The leading explanations are:
- Lower appetite. A 2024 study from Stanford Medicine found that metformin raises levels of Lac-Phe, an appetite-suppressing molecule that the body also produces after intense exercise.5
- Better insulin sensitivity, which can reduce insulin levels and the cravings and fat storage associated with insulin resistance.1
- GI effects. Nausea and changes in the gut, especially early on, can reduce how much people eat.
Metformin vs. GLP-1 Medications
| Metformin | Semaglutide (Wegovy) | Tirzepatide (Zepbound) | |
|---|---|---|---|
| Typical average weight loss in trials | About 2-3% | About 15% | About 20% |
| Approved for weight loss? | No (off-label) | Yes | Yes |
| Form | Pill, daily | Weekly injection or daily pill | Weekly injection |
| Cost | Low, generic | High without coverage | High without coverage |
Metformin is sometimes used alongside GLP-1 medications, especially in people with type 2 diabetes or prediabetes.3 If you're on or considering a GLP-1, our GLP-1 diet guide covers how to eat to get the most from it.
Side Effects and Safety
Common: diarrhea, nausea, stomach upset, gas and a metallic taste, mostly when starting or increasing the dose. Taking it with meals, starting low and increasing slowly, and using the extended-release form usually help.6
Important to know:
- Lactic acidosis is rare but serious and carries a boxed warning. Risk is higher with poor kidney function, heavy alcohol use, severe illness or dehydration. Metformin shouldn't be used if kidney function (eGFR) is below 30, and isn't recommended to start if it's between 30 and 45.6 It is also usually paused around procedures that use iodinated contrast dye.
- Vitamin B12: long-term use can lower B12 levels, so periodic checks are recommended.3,6
- Low blood sugar is uncommon with metformin alone but more likely if combined with insulin or a sulfonylurea.6
Dosing: prescribers usually start at 500 mg once or twice a day with food and increase gradually. The maximum is 2,550 mg a day for immediate-release and 2,000 mg a day for extended-release.6 For weight, the evidence points to taking at least 1,500 mg a day long-term, if tolerated.3 Your prescriber will set your dose.
Who Might Benefit?
A 2023 review in the Cleveland Clinic Journal of Medicine suggests metformin is most worth considering, off-label, for people with obesity who also have:3
- Prediabetes or insulin resistance
- PCOS
- Weight gain from antipsychotic medications
- A BMI of 35 or higher
- A reason to avoid or delay GLP-1 medications, such as cost or access
Eating to Get the Most From It
No medication replaces the basics, and with a drug whose effect is modest, they do most of the work. Build meals around lean protein, vegetables and fiber; cut back on sugary drinks and refined carbs; and keep portions consistent. Taking metformin with meals also eases stomach side effects. Our guide to the best foods for weight loss has the full list.
If consistency is the hard part, our Weight Loss Meal Plan delivers portion-controlled meals with macros printed on every label, or you can pick your own meals with Build-a-Meal Plan.
Frequently Asked Questions
Does metformin cause weight loss?
Often, but modestly. On average people lose about 2 kg (4-5 pounds), or 2-3% of body weight. About 30% of people lose 5% or more in the first year, and those responders tend to keep much of it off long-term.
How much weight can you lose on metformin?
In the Diabetes Prevention Program, people on metformin lost an average of 2.1 kg over about 2.8 years. Among those who lost at least 5% in the first year, the average loss was still 6.2% of starting weight 6 to 15 years later.
Is metformin approved for weight loss?
No. Metformin is FDA-approved for type 2 diabetes. Using it for weight loss or prediabetes is off-label, which is common and legal but a decision for your prescriber.
Will metformin make me gain weight?
Metformin is not associated with weight gain. It is generally weight-neutral or causes modest weight loss, which is one reason it's preferred over some other diabetes medications.
Can I take metformin with Ozempic or other GLP-1 medications?
They are often prescribed together, particularly for type 2 diabetes, and the combination doesn't usually cause low blood sugar on its own. Both can cause GI side effects, so starting them one at a time is common. Your prescriber decides whether the combination fits you.
Is metformin gluten-free?
Metformin itself doesn't contain gluten, but inactive ingredients vary by manufacturer. Ask your pharmacist to check your specific product.
References
- Bailey CJ. Metformin: historical overview. Diabetologia. 2017;60(9):1566-1576.
- Diabetes Prevention Program Research Group. Long-term safety, tolerability, and weight loss associated with metformin in the Diabetes Prevention Program Outcomes Study. Diabetes Care. 2012;35(4):731-737. View study
- Pantalone KM, et al. Should I consider metformin therapy for weight loss in patients with obesity but without diabetes? Cleve Clin J Med. 2023;90(9):545-548. View article
- Apolzan JW, et al. Long-term weight loss with metformin or lifestyle intervention in the Diabetes Prevention Program Outcomes Study. Ann Intern Med. 2019. Summary
- Stanford Medicine. Weight loss caused by common diabetes drug tied to "anti-hunger" molecule in study. March 18, 2024. View article
- Metformin dosage and prescribing information. Drugs.com.
This content is for educational purposes only and is not a substitute for advice from a qualified healthcare professional.
