In short
Metformin is a diabetes medication that produces modest weight loss for some people; it is not approved for weight management. GLP-1 medications are approved.
By Alsen Walker · Updated September 20, 2026
Metformin is a diabetes medication that produces modest weight loss for some people; it is not approved for weight management. GLP-1 medications are approved for it and produce substantially larger effects. Metformin is cheap, long-established and well tolerated by most, which is why it still comes up.
Prescribing metformin for weight loss alone is off-label. That is legal and reasonably common, and it means your insurance will not cover it on that basis, and the evidence base is thinner than for its approved uses.
For how this fits alongside the other comparisons, and what actually decides the choice, see Comparing GLP-1 Medications: How to Actually Choose.
What metformin does
It reduces glucose production by the liver and improves insulin sensitivity. Weight effects are secondary and generally modest, and it is not an appetite suppressant in the way these other medications are.
For some people it produces a little weight loss or prevents weight gain. For others it does nothing to the scale at all.
Where it genuinely fits
Type 2 diabetes, where it is a long-standing first-line treatment.
Prediabetes, where it is sometimes used to reduce progression risk, particularly alongside lifestyle change.
PCOS, where insulin resistance is often part of the picture and metformin is commonly used.
Cost-constrained situations, where it is inexpensive and available as a generic while GLP-1 coverage is refused.
Side effects
Gastrointestinal effects are common early: nausea, diarrhea, abdominal discomfort. These often settle, and extended-release forms are frequently better tolerated.
Long-term use is associated with reduced vitamin B12 absorption, which is worth periodic checking, particularly if you are also eating considerably less on a GLP-1.
Lactic acidosis is rare and is the reason kidney function matters for prescribing.
Taking both
Common in type 2 diabetes and a normal combination rather than an unusual one. Your prescriber decides whether both are appropriate.
Worth knowing that the gastrointestinal effects can overlap, so starting or increasing one while already on the other is a period to expect more symptoms.
Expectation setting
If you are hoping metformin will produce results comparable to a GLP-1, it generally will not. Its value is in glycaemic control, cost, and a long safety record, not in the magnitude of weight change.
Where it is being offered because GLP-1 coverage was refused, that is worth naming in the conversation, since appeal and exception routes may still be available.
Metformin is often what gets offered when GLP-1 coverage is refused, which is worth naming, since appealing that denial may still be available. For PCOS specifically, the best GLP-1 for PCOS covers where each fits.
Frequently asked questions
How much weight will metformin cause me to lose?
Generally modest and variable. Some people see none.
Is it a good alternative if I cannot afford a GLP-1?
It is inexpensive and may help, particularly with insulin resistance. Expect a smaller effect.
Can I take both?
Common in type 2 diabetes. A prescriber decision.
Does it help PCOS?
It is commonly used where insulin resistance is present. Discuss it with your clinician.
Do I need B12 checked?
Worth asking about with long-term use, and more so if your intake has fallen.
Will insurance cover it for weight loss?
Not usually, since that is off-label. It is inexpensive enough that this often matters less.
Sources and further reading
- National Institute of Diabetes and Digestive and Kidney Diseases (NIH). Prescription medications to treat overweight and obesity. www.niddk.nih.gov
- MedlinePlus (US National Library of Medicine). Semaglutide injection: drug information. medlineplus.gov
- MedlinePlus (US National Library of Medicine). Tirzepatide injection: drug information. medlineplus.gov
GLP1Hub content is for general information and is not medical advice. Prices and coverage rules change often, so confirm current details with the provider, your insurer and your prescriber. See our editorial standards and medical disclaimer.
