Metformin: A Pill for Better Health?

Updated June 2026. Originally published March 2019.

Doctors prescribe Metformin under several trade names, including Glucophage XR, Carbophage SR, Riomet, Fortamet, Glumetza, Obimet, Gluformin, Dianben, Diabex, Diaformin, Siofor, Metfogamma, and Glifor. The USDA cites its ancestor plant as a weed.

That ancestor is Galega officinalis — known as Professor Weed in the US — a Class A Federal Noxious Weed in 35 states and a plant listed in the database of poisonous plants. (Wiley)

History

The discovery of metformin traces back to the 17th century. Galega officinalis L., also known as the French lilac, served as a herbal remedy for the intense urination caused by diabetes mellitus in medieval times. The guanides abundant in French lilac are key compounds in lowering blood glucose, which led to the development of three biguanides: metformin, phenformin, and buformin. Among these, metformin proved the most useful because of its low toxicity. Researchers first synthesized it in 1922. European regulators approved it for diabetes treatment in the 1950s, and the FDA followed in 1994. It now sits on the World Health Organization’s List of Essential Medicines.

Purpose

Metformin is the first-line medication prescribed to over 150 million patients worldwide for type 2 diabetes, particularly in people who are overweight. Doctors also use it for polycystic ovary syndrome (PCOS) and some insulin-resistance conditions.

The molecular mechanism of metformin remains incompletely understood. Multiple proposed mechanisms include: inhibition of the mitochondrial respiratory chain (complex I); activation of AMP-activated protein kinase (AMPK); inhibition of glucagon-induced elevation of cyclic adenosine monophosphate (cAMP) with reduced protein kinase A (PKA) activation; inhibition of mitochondrial glycerophosphate dehydrogenase; and effects on gut microbiota. The complexity here matters — and directly connects to the exercise interference problem described below.

Why consider it for longevity?

Metformin’s primary effect is decreasing liver glucose production. It also sensitizes cells to insulin across multiple tissues — liver, skeletal muscle, endothelium, adipose tissue, and the ovary.

Several findings support its potential beyond diabetes management:

• A 2017 review and meta-analysis found that people with diabetes taking metformin had 7% lower all-cause mortality, along with reduced rates of breast, gastrointestinal, liver, and pancreatic cancer compared to those on other therapies.
• A large population-based study compared records of 78,000 diabetic patients treated with metformin against 78,000 matched non-diabetic controls. Mortality in metformin-treated diabetic patients was similar to the matched non-diabetic group. Among patients in their 70s, mortality was actually reduced by roughly 15% compared to non-diabetic controls — suggesting metformin’s protective action may extend beyond effects on specific age-related diseases.
• Epidemiologic studies consistently show an association between metformin use and decreased cancer risk and cancer mortality. Researchers propose mechanisms involving reductions in insulin levels, improved insulin signaling, decreased IGF-1 activity (central to mammalian longevity), and reduced cellular senescence.
• From various studies, 25–45% of people are non-responders to metformin — meaning they get the side effects without the metabolic benefits. This is a clinically significant caveat for anyone considering it off-label.

The TAME trial — still not fully enrolled

The TAME (Targeting Aging with Metformin) trial represents the most important test of metformin’s longevity potential — and its decade-long struggle to get funded reflects how hard it is to run a clinical trial on an off-patent drug with no commercial sponsor.

The proposed design: 3,000 participants aged 65–79 at 14 medical centers, randomized to metformin or placebo, followed for six years. The trial aims to test whether metformin delays the onset of age-related diseases as a composite endpoint — a design the FDA approved in principle, which is itself a landmark: the FDA has not traditionally recognized aging as a treatable indication, and TAME’s FDA-approved endpoint structure could open the door for future longevity drug development even if metformin itself proves unremarkable.

The funding reality as of mid-2026: the trial remains only partially funded. The National Institute on Aging has allocated approximately $5 million. The full trial costs an estimated $45–70 million, and pharmaceutical companies have no interest in funding a generic drug trial with no patent protection. Dr. Nir Barzilai, the trial’s principal investigator at Albert Einstein College of Medicine, has spent years piecing together philanthropic funding. Multiple attempted start dates have come and gone since the FDA green-lit the design in 2019. As of August 2025, Barzilai told reporters the positive evidence for metformin “is mounting” — but TAME still has not enrolled its full patient cohort.

The MILES (Metformin in Longevity Study) trial, which concluded in 2018, showed improved insulin sensitivity but also found significantly reduced gene expression in muscles — a concern that the subsequent exercise research below has sharpened considerably.

The exercise interference problem — a significant development

One of the most important updates since this article was first written concerns metformin’s interaction with exercise. Multiple high-quality studies now show that metformin interferes with some of the most important adaptations that exercise produces:

A 2022 study published in Obesity found that metformin use reduced VO2 max improvements by roughly half in people with hyperglycemia who underwent aerobic training — 12.7% improvement in the metformin group versus 25.3% in the exercise-only group. The mechanism runs through metformin’s inhibition of mitochondrial complex I: the same pathway that gives metformin its glucose-lowering effects also limits the mitochondrial adaptations that make exercise cardioprotective.

The March 2025 MET-PREVENT trial, published in The Lancet Healthy Longevity, found that metformin did not improve physical performance, activities of daily living, or quality of life in older people with sarcopenia and frailty — and produced a high number of adverse events. That trial also cited the MASTERS trial finding that metformin blunts muscle hypertrophy in response to progressive resistance exercise training in older adults.

Rutgers researchers, publishing in the Journal of Clinical Endocrinology in November 2025, found that metformin blunted vascular insulin sensitivity improvements after exercise training in adults at risk for metabolic syndrome — adding cardiovascular adaptation to the list of exercise benefits the drug appears to diminish.

An August 2025 paper in the Journal of Applied Physiology confirmed the same mechanistic picture in mice: metformin suppressed the mitochondrial and transcriptional response to exercise, identifying a conserved pathway through which the drug limits training adaptation.

What this means in practice: For people taking metformin specifically to prevent age-related disease in the absence of diabetes, the evidence now suggests a meaningful trade-off. Metformin may provide metabolic and longevity-associated benefits on its own, but it appears to meaningfully reduce the cardiovascular, muscular, and metabolic adaptations that exercise produces — particularly VO2 max gains and muscle hypertrophy. Given that exercise is one of the most powerful interventions for longevity and VO2 max is one of the strongest predictors of mortality, this trade-off deserves serious weight in any discussion about off-label metformin use in otherwise healthy people.

This concern is less acute for people who are diabetic or have metabolic syndrome, where metformin’s glucose-lowering benefits are substantial and well-established. For healthy, active individuals considering metformin purely as a longevity supplement, the exercise interference data is a meaningful reason for caution. Discuss it directly with your personal health team.

Dosage

• Doses range from 500 mg to 2,500 mg per day depending on formulation. See Mayo Clinic recommendations for specifics.
• Metformin requires a doctor’s prescription in the United States.
• Oral bioavailability is 50–60% under fasting conditions; the drug absorbs slowly.
• Metformin does not metabolize. The kidneys excrete it unchanged via tubular secretion; it becomes undetectable in blood plasma within 24 hours of a single oral dose. Average plasma elimination half-life is 6.2 hours, though it distributes into red blood cells with a much longer half-life of 17.6 hours.

Clinical trials

• Over 1,600 completed clinical trials have studied metformin across a wide range of conditions.
• TAME trial: Targeting Aging with Metformin — the landmark aging trial described above. Still recruiting and fundraising as of mid-2026.
• Metformin and Aging Study in PreDiabetes Adults: 25-patient Phase 3 study.
• MILES: Concluded May 2018. Showed improved insulin sensitivity alongside a concerning reduction in muscle gene expression.
• MET-PREVENT (Lancet Healthy Longevity, March 2025): Randomized controlled trial in older adults with sarcopenia. Metformin failed to improve physical performance and produced significant adverse events.
• Ongoing trials include evaluation of metformin’s role in mild cognitive impairment prevention, cancer (rectal, endometrial), and PCOS management.
• Berberine vs. metformin comparison: Short-term head-to-head data suggests comparable glucose-lowering effects at equivalent doses, with berberine showing additional lipid benefits. Keep Health’s ALA vs. Berberine article covers this comparison in detail.

Side effects and adverse events

• Metformin is generally well tolerated.
• Common side effects include diarrhea, nausea, and abdominal pain — most frequent when starting treatment or with dose increases.
• Low risk of causing hypoglycemia (low blood sugar), unlike some other diabetes medications.
• Lactic acidosis is a concern if prescribed inappropriately or at excessive doses, particularly in people with kidney impairment.
• Should not be used in those with significant liver disease or kidney problems.
• Significantly reduced gene expression in muscles (MILES trial finding), and now more broadly confirmed interference with exercise-induced cardiovascular and muscular adaptations.
• No clear harm from use during pregnancy, though insulin is generally preferred for gestational diabetes.
• Metformin depletes vitamin B12 over time with long-term use — a clinically meaningful effect that warrants periodic monitoring for anyone taking it chronically.

Leading scientists taking metformin

Several prominent longevity researchers take metformin off-label as a preventive measure:

• Ray Kurzweil
• David Sinclair
• Nobel laureate James Watson
• Robert Hariri, co-founder of Human Longevity Cellular Therapeutics

Note: Ned David, co-founder of Unity Biotechnology (a name that appeared in earlier versions of this list), is no longer relevant here — Unity dissolved in September 2025. See Investment Opportunities for more on the company’s closure.

The honest bottom line

Metformin has been prescribed to hundreds of millions of people for decades, has one of the largest observational evidence bases of any medication, and costs approximately five cents per pill as a generic. The epidemiological case for longevity benefits in diabetic patients is compelling. The mechanistic case — AMPK activation, reduced cellular senescence, anti-inflammatory effects — is scientifically interesting.

What has sharpened considerably since this article was first published is the exercise interference picture. Multiple well-designed trials now consistently show that metformin reduces VO2 max gains, blunts muscle hypertrophy, and diminishes cardiovascular adaptations from exercise. For people who exercise regularly and are considering metformin off-label purely for longevity, that trade-off deserves serious attention — especially since exercise itself is arguably the most evidence-backed longevity intervention available.

For people with type 2 diabetes, prediabetes, metabolic syndrome, or PCOS, the benefit-risk calculation looks much more favorable. Metformin remains the appropriate first-line choice for those conditions.

The TAME trial, if it ever gets fully funded and completes its six-year follow-up, will provide the clearest answer to date on whether metformin meaningfully delays aging in people who don’t have diabetes. Until then, anyone considering it off-label should have that conversation with a knowledgeable physician — not a longevity influencer.

Data sources

• Wikipedia — Metformin
• Healthspancampaign.org — Dr. Nir Barzilai on the TAME study
• Wired — This Pill Promises to Extend Life for a Nickel a Pop
• Wiley — Galega officinalis history
• AFAR.org — TAME trial
• NIH — Berberine vs. Metformin
• FrontiersIn.org — Metformin mechanisms
• Lancet Healthy Longevity — MET-PREVENT trial, March 2025
• ScienceDaily — Rutgers metformin/exercise study, November 2025
• Lifespan.io — Nir Barzilai interview, August 2025
• Fight Aging! — TAME funding status, 2024