Questioning the hype around metformin as a longevity drug

Critics warn that the popularity of metformin for extending lifespan is driven by anecdote rather than solid evidence, amid ongoing debate over the drug’s true benefits for healthy ageing.

In a recent Substack essay, Matt Cook takes aim at the growing enthusiasm for metformin as a longevity drug, arguing that the cheap diabetes medicine is being promoted far beyond the evidence. He notes that metformin has been used for decades to lower blood sugar, and that some people now take it despite not having diabetes, on the theory that it might slow ageing or add years to life. The attraction is obvious: it is inexpensive, familiar and widely prescribed. But Cook’s central point is that popularity is not the same as proof.

The drug’s safety record is often presented as one of its strongest selling points, yet Cook argues that the most serious concern has always been the rare risk of lactic acidosis, a dangerous build-up of lactic acid in the blood. The Cleveland Clinic says metformin is the main biguanide in use today and is commonly prescribed for type 2 diabetes, but it is not suitable for people with severe kidney disease or metabolic acidosis. Mayo Clinic likewise says it is used for high blood sugar in type 2 diabetes, and works by reducing sugar production in the liver, lowering intestinal absorption and improving the body’s response to insulin.

Much of the longevity debate has centred on the proposed TAME trial, short for Targeting Aging with Metformin. Researchers described it as a six-year, double-blind, placebo-controlled study involving about 3,000 adults aged 65 to 79 who did not have diabetes but were at high risk of age-related disease. Its aim was to test whether metformin could delay the accumulation of multiple diseases associated with ageing. Yet Cook says he could not find a documented enrolment record on ClinicalTrials.gov, and a 2026 status update from StackingYears said the trial remained unfunded, had not enrolled participants and had produced no efficacy results by mid-2026.

Cook also points to evidence that the drug may not deliver the benefits its boosters expect in healthy, active older adults. He cites a study in Kentucky and Alabama in which 94 people over 65, all of whom lifted weights three times a week for 14 weeks, were split between metformin and placebo while neither participants nor researchers knew who received which. The point, he suggests, is that the real question is not whether metformin can be useful for diabetes, where it remains a standard treatment, but whether it improves ordinary health in people taking it for prevention or longevity. For now, the answer remains contested.