In one study conducted by the manufacturer, metformin (dose: up to 2,550 mg/day) was compared to a placebo treatment (an inactive agent) in a study lasting 29 weeks.

• The average weight of people at the start of the study was 91 kg (201 lbs) (91 kg) in those taking only metformin and 94 kg (206) in the placebo group.
• After 29 weeks, people in the metformin group lost an average of 0.7 kg (1.4 lbs) vs. 1.1 kg (2.5 lbs) in the placebo group.

Study 2: Metformin vs. glyburide

Another study done by the manufacturer evaluated weight loss between metformin, metformin combined with glyburide (an oral sulfonylurea for type 2 diabetes), and glyburide used alone.

• In the group receiving metformin alone, the average body weight at the start of the study was 93 kg (204 lbs). By the 29th week, patients in this group had lost an average of 3.8 kg (8.4 lbs).
• In the group taking metformin combined with glyburide, the average weight at the start of the study was 92 kg (202 lbs) and they gained an average of 0.4 kg (0.9 lbs) at 29 weeks.
• In those taking glyburide alone who weighed an average of 92 kg (203 lbs) at baseline, a weight loss of 0.3 kg (0.7 lb) was seen.

Study 3: Metformin vs. rosiglitazone or glyburide

In a study with over 4,300 obese patients recently diagnosed with type 2 diabetes, patients were given either rosiglitazone (a thiazolidinedione agent used to treat type 2 diabetes), metformin, or glyburide (a sulfonylurea) as initial treatment.

• Body weights were assessed over a 5 year period. In the metformin group, the mean weight decreased by 2.9 kg (6.4 lbs). More frequent gastrointestinal (stomach) side effects occurred in this group compared to the others.
• In the rosiglitazone group, the average weight increased by 4.8 kg (10.6 lbs) and was associated with greater edema (fluid retention) and LDL (“bad” cholesterol) elevations.
• In the glyburide group, patients gained 1.6 kg (3.5 lbs) over the first year, but weight stabilized thereafter. Higher rates of low blood sugar (hypoglycemia) were seen in the glyburide group vs. other treatments.

Study 4: Metformin vs. dulaglutide (a GLP-1 agonist)

In a trial comparing metformin with dulaglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist, weight loss at 26 and 52 weeks was similar to the dulaglutide 1.5 mg dose but smaller with the dulaglutide 0.75 mg dose.

• metformin: loss of 2.22 kg (4.9 lbs)
• dulaglutide (1.5 mg): loss of 2.29 kg (5 lbs)
• dulaglutide (0.75 mg): loss of 1.36 kg (3 lbs)

Study 5: Metformin plus sitagliptin (DPP-4 inhibitor) vs. metformin alone

Metformin is also combined with sitagliptin (brand name: Januvia), a 2 diabetes treatment in a class called dipeptidyl peptidase-4 (DPP-4) inhibitors. Brand names for the combinations of sitagliptin and metformin are Janumet or Janumet XR.

In 24-week long studies conducted by the sitagliptin manufacturer, when metformin was used alone or with sitagliptin, metformin led to a small but similar weight loss in most patients.

• Metformin alone: weight loss of 0.6 kg to 1.3 kg (1.3 lb to 2.9 lb)
• Januvia (sitagliptin) + metformin: weight loss of 0.6 kg to 1.3 kg (1.3 lb to 2.9 lb)

Learn More: Does Januvia cause weight gain or loss?

Is metformin approved for weight loss?

Metformin is not specifically approved to be used for weight loss as a stand-alone therapy, but may lead to a moderate weight loss in some people. Metformin, when used with diet and exercise, is approved by the FDA for blood sugar control in the treatment of type 2 diabetes in adults and children 10 years of age and older.

Some studies have shown that metformin can lead to weight loss when evaluated in non-diabetic individuals with obesity.

• In one 6-month long, non-randomized study, researchers examined the effectiveness of metformin (doses up to 2,500 mg per day) to reduce weight in 154 obese and overweight patients (BMI ≥27 kg/m) with / without insulin resistance. They also included 45 untreated patients as controls.
• The average weight loss in the group that received metformin was 5.8 kg (12.8 lbs) ±7 kg (± 15 lbs). Untreated controls gained 0.8 kg (1.8 lbs) ± 3.5 kg (± 7.7 lbs) on average. Patients with severe insulin resistance lost significantly more weight as compared to insulin sensitive patients.
• Overall, researchers observed a weight loss of 10% or more in 16.2% and a weight loss of at least 5% in 47.4% of the 154 metformin-treated patients

The authors concluded that metformin was an effective drug to reduce weight in a naturalistic outpatient setting in insulin sensitive and insulin resistant overweight and obese patients.

Which diabetes treatments work best for weight loss?

Examples of type 2 diabetes medicines that are associated with weight loss include:

• alpha-glucosidase inhibitors: acarbose (Precose) and miglitol (Glyset)
• amylin analogs: pramlintide (Symlin)
• glucagon-like peptide 1 (GLP-1) agonists (“incretin mimetics”): dulaglutide (Trulicity), exenatide (Bydureon), exenatide (Byetta), semaglutide (Ozempic, Rybelsus), liraglutide (Victoza), lixisenatide (Adlyxin).
• GLP-1 / GIP (glucose-dependent insulinotropic polypeptide ) receptor agonist: tirzepatide (Mounjaro)
• sodium glucose cotransporter 2 (SGLT-2) inhibitors: canagliflozin (Invokana), ertugliflozin (Steglatro), dapagliflozin (Farxiga), empagliflozin (Jardiance)

Note: Liraglutide (Saxenda) and semaglutide (Wegovy) are approved for weight loss in people with or without type 2 diabetes. Tirzepatide (Mounjaro) has also been shown in clinical trials to be useful for weight loss; however, it is not currently approved as a weight loss drug. The manufacturer submitted approval for this use to the FDA in 2022, with a decision expected in 2023.

Type 2 diabetes medicines that tend to be weight neutral, not increasing or decreasing weight substantially, include:

• metformin
• alpha-glucosidase inhibitors such as acarbose (Precose) and miglitol (Glyset)
• dipeptidyl peptidase-4 (DPP-4) inhibitors, such as sitagliptin (Januvia), linagliptin (Tradjenta), saxagliptin (Onglyza), alogliptin (Nesina)

This is not all the information you need to know about metformin for safe and effective use and does not take the place of your health care provider’s directions. Review the full product information and discuss this information and any questions you have with your doctor or other health care provider.