Rapamycin and metformin for longevity: what is actually known

Rapamycin and metformin are the two prescription drugs most often taken off-label in the hope of slowing ageing. The honest position is this: rapamycin has the strongest animal lifespan data of any drug, and a clear mechanism through the mTOR pathway, but there is no human trial showing it extends life or healthspan. Metformin's anti-ageing case rests mainly on observational data in people who already have diabetes, and the one large trial designed to test it in healthy adults has not reported. Both are unlicensed for ageing in the UK. Neither is a proven longevity drug.

The rapamycin rationale: a real mechanism

Rapamycin (the drug name is sirolimus) was found in soil from Easter Island and developed as an immunosuppressant. Its longevity interest comes from its target: a protein complex called mTOR, short for mechanistic target of rapamycin. mTOR is a master nutrient sensor. When food, especially protein, is plentiful, mTOR is active and tells the cell to grow and build. When mTOR is dialled down, the cell shifts into a maintenance mode, recycling damaged components through a process called autophagy. Slowing mTOR with rapamycin partly mimics the state the body enters during fasting or calorie restriction, the most reliable lifespan extender across species.¹ If you want the fuller picture of that cleanup process, see our explainer on autophagy and fasting.

The animal data are genuinely striking. In 2009, a multi-site study run through the US Interventions Testing Program reported that rapamycin extended both median and maximum lifespan in genetically varied mice, even when the drug was started at the equivalent of late middle age, around 600 days. The gain was roughly 14% for females and 9% for males.² No other drug has matched this. It remains the headline result that drives the entire field.

What the human evidence actually shows

Human data are thin and indirect. The most cited result is not even rapamycin itself: in a 2014 trial, the related drug everolimus (a rapalog) improved the elderly immune response to flu vaccination by about 20% and reduced markers of immune ageing.³ That is a measure of immune function over six weeks, not lifespan, and used a different molecule.

The first proper randomised trial of rapamycin itself in healthy adults was PEARL, reported in 2024. It enrolled normally ageing adults, gave 5 or 10 mg per week of compounded rapamycin or placebo for 48 weeks, and tracked them remotely. The good news: it was broadly safe, with side-effect rates similar to placebo. The sobering news: it missed its primary outcome, a change in visceral fat, and the scattered positive signals (such as lean mass and self-reported pain in women on the higher dose) were secondary findings in a modestly sized study.⁴ It tells us low-dose weekly rapamycin is reasonably tolerated for a year. It tells us nothing about whether it slows ageing.

Off-label "longevity dosing" and its real risks

Despite the absent evidence, a clinic-and-influencer ecosystem now prescribes rapamycin off-label, typically around 6 mg once weekly, the intermittent schedule being an attempt to capture the benefit while avoiding the side effects of continuous dosing.⁵ The risks are not hypothetical. At higher or daily doses, sirolimus is meaningfully immunosuppressive, which is precisely why transplant patients take it. Known effects include mouth ulcers, raised blood lipids, impaired glucose tolerance and delayed wound healing.⁵ Whether weekly micro-dosing avoids these in healthy people over years is simply unstudied.

The metformin story

Metformin is the world's most prescribed diabetes drug, cheap and broadly safe, which is part of its appeal as a longevity candidate. It activates an energy sensor called AMPK and indirectly restrains mTOR, so it shares some theoretical ground with rapamycin. The interest in ageing was sparked largely by a 2014 UK study using the CPRD database, which found that people with diabetes on metformin alone had slightly longer survival than matched non-diabetic controls.⁶ That is a provocative finding, but it is observational, and the metformin group were healthier diabetics by definition, so the comparison is not as clean as it first sounds.

To settle the question, Nir Barzilai's group designed the TAME trial (Targeting Aging with Metformin): around 3,000 non-diabetic adults aged 65 to 79, randomised to metformin 1,500 mg a day or placebo, with a composite endpoint of cardiovascular disease, cancer, dementia or death.⁷ It is a landmark in principle, the first trial to treat ageing itself as the target. In practice it has struggled for full funding and has not reported results, so it cannot yet support any claim.

The exercise-blunting question

There is also a genuine downside signal for fit, active people. In a 2019 randomised trial, older adults who took metformin while doing aerobic training gained less cardiorespiratory fitness and showed blunted mitochondrial adaptations compared with those on placebo.⁸ A companion trial found metformin similarly blunted muscle growth from resistance training.⁹ Exercise is the best-evidenced anti-ageing intervention there is, so a drug that dampens its benefits is a real concern for anyone training seriously. And when metformin was tested directly in frail older people in the UK MET-PREVENT trial in 2025, it did not improve physical performance and caused a high rate of side effects.¹¹

A sober verdict

Here is the balanced read. Rapamycin has the most compelling mechanism and the best animal lifespan data in the entire longevity field, which is exactly why it is taken seriously by serious researchers. But the gap between a mouse result and a proven human benefit is wide, and right now it is unbridged. Metformin's benefits are clearest where they are licensed: in type 2 diabetes. Its anti-ageing case is weaker, partly observational, undercut by the exercise-blunting data, and still waiting on the trial meant to test it.

For most people the rational move is to bank the interventions that already have strong human evidence, resistance and aerobic exercise, sleep, not smoking, and managing blood pressure and metabolic health, before reaching for an unlicensed drug on the strength of mouse data. If you are minded to experiment anyway, do it with a doctor, with monitoring, and with clear eyes about what is known. Our start here guide and the wider insights can help you think this through, and the stack builder can weigh any intervention against better-evidenced options.

This article is educational and does not constitute medical advice, diagnosis, or a treatment recommendation. Medication uses described as “off-label” are not licensed for that purpose in the UK and should only be considered under qualified clinical supervision. Always speak to your GP, pharmacist, or a registered specialist before starting, stopping, or changing any treatment. If you have severe or alarm symptoms - unintentional weight loss, blood in your stool, difficulty swallowing, persistent vomiting, a fever, or severe pain - seek urgent medical care.