Metformin is FDA-approved only for type 2 diabetes, but doctors prescribe it off-label for a surprisingly wide range of conditions. The most common non-diabetes uses include polycystic ovary syndrome (PCOS), weight management, and cardiovascular risk reduction. It’s also being investigated for cancer prevention, anti-aging, and even long COVID. Here’s what the evidence actually shows for each use.
Polycystic Ovary Syndrome (PCOS)
PCOS is probably the best-established off-label use for metformin. Women with PCOS have abnormalities in how their bodies handle insulin, and those abnormalities drive many of the syndrome’s hallmark symptoms: irregular periods, excess androgen (male hormone) production, and difficulty ovulating. Metformin works by making the body more sensitive to insulin, which in turn helps lower androgen levels and can restore regular ovulation.
The goal of treatment is typically to induce regular ovulation and menstrual cycles, which also improves fertility. Doctors usually start with a low dose and gradually increase it over several weeks to minimize digestive side effects like nausea and diarrhea. A typical ramp-up schedule starts at 500 mg once daily and builds to 1,000 mg twice daily over about a month. Metformin is sometimes used alongside other fertility treatments for women with PCOS who are trying to conceive.
Weight Loss in People Without Diabetes
Metformin produces modest but meaningful weight loss even in people with completely normal blood sugar. A retrospective study found that people without diabetes or prediabetes lost an average of 7.4% of their body weight after 12 months on metformin. That’s nearly identical to the 7.3% lost by people with diabetes or prediabetes taking the same drug, suggesting the weight loss effect doesn’t depend on correcting high blood sugar.
For someone weighing 200 pounds, that translates to roughly 15 pounds over a year. It’s not as dramatic as newer weight loss medications, but metformin costs a fraction of the price and has decades of safety data behind it. The Cleveland Clinic Journal of Medicine has noted that metformin “should also be considered as an initial and adjunctive treatment for obesity,” based on clinical experience and results from a large randomized diabetes prevention trial. Some doctors prescribe it as a first step or as a complement to other weight management strategies.
Preventing Weight Gain From Psychiatric Medications
Second-generation antipsychotic medications are effective for conditions like schizophrenia and bipolar disorder, but they frequently cause significant weight gain. Metformin is one of the best-studied options for countering this side effect. A 2025 network meta-analysis found that metformin significantly reduced weight compared to placebo in both short-term and long-term use alongside antipsychotics.
In longer-term studies, metformin users gained about 2 kg (roughly 4.4 pounds) less than those on placebo. The researchers concluded that metformin and one other medication “appear to have the strongest evidence for treating weight gain in the target group.” This matters because antipsychotic-related weight gain isn’t just cosmetic. It raises the risk of diabetes, heart disease, and metabolic syndrome, and it’s one of the most common reasons people stop taking medications they need.
Cardiovascular Protection
A large 2025 retrospective study analyzed electronic health records from 101 healthcare organizations to see whether metformin protects the heart in people who don’t have diabetes. Researchers compared roughly 46,500 non-diabetic patients with high blood pressure and high cholesterol who took metformin against a matched group of the same size who didn’t.
The results were striking for heart attacks specifically: the non-metformin group had a 59% higher risk of heart attack compared to those taking metformin. The metformin group also showed modestly lower rates of heart failure and atrial fibrillation. These are observational findings, not proof from a randomized trial, but they add to a growing body of evidence that metformin does something beneficial for blood vessels and heart tissue beyond just lowering blood sugar.
Cancer Risk Reduction
Multiple large observational studies have found that people taking metformin develop certain cancers at lower rates. The data is most extensive for three cancer types.
- Breast cancer: Several studies have found risk reductions ranging from 19% to 56% among metformin users. The effect on breast cancer mortality appears even stronger, with one study reporting a 35% reduction in deaths from breast cancer.
- Colorectal cancer: One study of long-term metformin users (five or more years) found a 64% lower incidence of colorectal cancer. Even those who used it for five to ten years saw a 40% reduction.
- Prostate cancer: Studies show risk reductions between 4% and 45%, with the strongest effects seen in cancer-specific mortality rather than incidence alone.
These numbers come from observational studies, which means they can’t prove metformin directly prevents cancer. People taking metformin may differ from non-users in ways that independently affect cancer risk. Still, the consistency of the findings across different cancer types and different research groups has generated serious scientific interest. Metformin appears to influence cellular processes related to energy metabolism and cell growth, which could plausibly slow tumor development.
Anti-Aging and Longevity
The most ambitious proposed use for metformin is as an anti-aging drug. The American Federation for Aging Research is working to launch the TAME trial (Targeting Aging with Metformin), which would test whether metformin delays the development of age-related diseases like heart disease, cancer, and dementia. The trial’s broader goal is even more radical: to get the FDA to recognize aging itself as a treatable condition.
The biological rationale is that metformin influences metabolic and cellular processes associated with aging, potentially slowing decline across multiple organ systems simultaneously. If the trial succeeds, it would represent a fundamental shift in medicine, from treating each age-related disease separately to targeting the underlying aging process. As of 2025, the trial is still in the fundraising phase and has not yet begun enrolling patients, so the anti-aging benefits remain theoretical.
Other Conditions Under Investigation
Metformin is also being studied or used off-label for fatty liver disease (where insulin resistance plays a central role), rheumatoid arthritis, lupus, and long COVID. For gestational diabetes prevention, a small trial in high-risk pregnant women found no significant effect, though the study was too small to draw firm conclusions and struggled with recruitment due to safety concerns about use during pregnancy.
The common thread across nearly all of these uses is metformin’s ability to improve insulin sensitivity and influence how cells process energy. Because insulin resistance and metabolic dysfunction contribute to so many different conditions, a drug that corrects those pathways has an unusually broad potential reach. That breadth, combined with metformin’s low cost, well-understood side effect profile, and more than 60 years of clinical use, is why it keeps showing up in research far outside its original purpose.