Short answer: metformin is approved for type 2 diabetes, not for aging. Taking it for longevity is off-label. Human evidence that it slows aging in people without diabetes is early: the registered pilot we could read studied 14 people for 6 weeks per treatment and measured gene activity, not lifespan or disease. The label's main risks are stomach side effects, lower vitamin B12 over time and a rare but serious complication called lactic acidosis.
Label quotes below come from the metformin hydrochloride tablets prescribing information on DailyMed, read on 1 October 2026.
What metformin is approved for
The metformin label: "Metformin hydrochloride tablets are indicated as an adjunct to diet and exercise to improve glycemic control in adults and pediatric patients 10 years of age and older with type 2 diabetes mellitus." Nothing in the label covers aging, healthspan or prevention in people without diabetes.
What the human evidence actually measured
The longevity case for metformin rests mostly on animal studies and on observational data from people with diabetes. The registered human trial we could read is MILES, the Metformin in Longevity Study (NCT02432287), which ClinicalTrials.gov lists as completed with 16 participants enrolled.
Its published results describe the design: "We studied ~70-year-old participants (n = 14) in a randomized, double-blind, placebo-controlled, crossover trial in which they were treated with 6 weeks each of metformin and placebo." The MILES authors report that "As expected, metformin therapy lowered 2-hour glucose, insulin AUC, and insulin secretion compared to placebo", along with changes in gene expression in muscle and fat tissue.
That is a mechanism study. It did not measure lifespan, frailty, or the onset of age-related disease.
You may have read about TAME, a proposed large trial of metformin and aging. When we searched ClinicalTrials.gov on 1 October 2026 for "Targeting Aging with Metformin", we found no registered record, so we cannot report a status, a size or a result for it.
The lactic acidosis boxed warning
The metformin label's boxed warning: "Postmarketing cases of metformin-associated lactic acidosis have resulted in death, hypothermia, hypotension, and resistant bradyarrhythmias. The onset of metformin- associated lactic acidosis is often subtle, accompanied only by nonspecific symptoms such as malaise, myalgias, respiratory distress, somnolence, and abdominal pain."
The metformin label ties the risk closely to kidney function: "Do not use in patients with eGFR below 30 mL/minute/1.73 m 2". It also notes that the drug "may need to be discontinued at time of, or prior to, iodinated contrast imaging procedures", the dye used in some CT scans.
Common side effects
The metformin label: "the most common adverse reactions (>5.0%) are diarrhea, nausea/vomiting, flatulence, asthenia, indigestion, abdominal discomfort, and headache."
On long-term use the metformin label adds: "Metformin may lower vitamin B12 levels. Measure hematological parameters annually and vitamin B12 at 2 to 3 year intervals". Low B12 can cause fatigue and nerve symptoms, which is worth knowing if your reason for taking metformin is energy.
Questions to ask a clinician before starting
- What is my kidney function (eGFR), and how often will you recheck it?
- Will you test my vitamin B12 levels?
- What should I do before a CT scan with contrast?
- What outcome are we expecting, and how will we know if it is working?
Who prescribes metformin online, at prices we verified
Of the 31 clinics we track, three list metformin among their longevity treatments. AgelessRx shows it "Starting at $25 / mo" on its metformin page (read October 28, 2026). HealthRX lists "Metformin ER 500 mg" at $107/month on its 12-month plan, or $134 billed monthly (read October 28, 2026). Peter MD lists Metformin 500 mg at $60 for a 30-day plan, $110 for 60 days or $160 for 90 days, plus a $70 physician consultation if you are not already a patient (read October 28, 2026).
Medical disclaimer: this article summarizes the FDA label and one registered pilot trial and is not medical advice. Metformin is a prescription drug; take it only under a licensed clinician who checks your kidney function.
