No source used here says metformin is approved for weight loss. The prescribing information for metformin ER tablets states use as an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes mellitus. Studies that report weight differ in who they studied and in what they found.
What the dose-response study in the prescribing information reported
The prescribing information for metformin ER tablets describes a 16-week dose-response study in type 2 diabetes. It lists the mean change in body weight from baseline to week 16 for each arm, including placebo.
| Arm | Mean change in body weight, baseline to week 16 |
|---|---|
| 500 mg once daily | -1.3 lbs |
| 1,000 mg once daily | -1.3 lbs |
| 1,500 mg once daily | -0.7 lbs |
| 2,000 mg once daily | -1.5 lbs |
| 1,000 mg twice daily | -2.2 lbs |
| Placebo | -1.8 lbs |
Weight fell in every arm, including placebo. The excerpt used here does not give a statistical comparison between arms.
What the Diabetes Prevention Program follow-up reported
The Diabetes Prevention Program (DPP) assigned nondiabetic persons with elevated fasting and post-load plasma glucose concentrations to placebo, metformin, or a lifestyle-modification program, and it reported diabetes incidence. It was not a weight-loss trial. Its follow-up, the Outcomes Study, also reported weight.
In the unblinded follow-up (metformin versus placebo; the abstract does not state a dose), weight loss remained significantly greater in the metformin group than in the placebo group (2.0 vs. 0.2%, P < 0.001) and was related to the degree of continuing metformin adherence. At the 10-year follow-up, the original lifestyle group lost, then partly regained weight, while the modest weight loss with metformin was maintained.
What the meta-analyses reported
- A systematic review and meta-analysis of randomized trials concluded that metformin was associated with a modest weight reduction in obese nondiabetic patients and that further high-quality and better powered studies are needed. In adults without diabetes it reported a significant percentage change in BMI of -2.53% (-2.90, -2.17) at the dose 1700 mg/day, with doses across trials ranging from 500 to 2550 mg/day.
- A meta-analysis of randomized trials in persons at risk for diabetes (doses not stated in the abstract) concluded, in the authors' words, that metformin treatment "improves weight, lipid profiles, and insulin resistance."
- A systematic review and meta-analysis of placebo-controlled randomized trials of metformin monotherapy in drug-naive patients with type 2 diabetes mellitus (doses not stated in the abstract) found no evidence for the effects on weight.
Other groups and general statements about weight medicines
A meta-analysis of randomized placebo-controlled trials in people taking antipsychotics (metformin dose varied; subgroup analyses found outcomes influenced by metformin dose) wrote that its results suggest adjunctive metformin is a reasonable choice for antipsychotic-induced weight gain and metabolic abnormalities. A systematic review and meta-analysis of randomized trials in women with polycystic ovary syndrome (metformin at any dose and any duration, per the abstract) found that metformin alone compared with lifestyle showed similar BMI at 6 months.
A NIDDK page on prescription medications for overweight and obesity says that by choosing an off-label medication, a health care professional may prescribe a drug approved for treating a different medical problem. It also says that on average, after 1 year, adults who take prescription medications as part of a lifestyle program lose 3% to 12% more of their starting body weight than people in a lifestyle program who do not take medication. These statements are about weight medicines in general. They do not name metformin, so the 3% to 12% figure is not a metformin result.
What this does not tell you
These studies enrolled different groups: people with type 2 diabetes, adults without diabetes, persons at risk for diabetes, people taking antipsychotics, and women with polycystic ovary syndrome. A result in one group does not carry over to another. Doses vary or are not stated in the abstracts, and the review conclusions are the authors' own.
The meta-analyses above reach different conclusions about weight, and the placebo arm in the dose-response study in the prescribing information also lost weight. None of these sources says how much weight any one person would lose. They do not cover side effects or risks. A licensed provider decides whether any medicine fits a person's situation.