Rapamycin

Rapamycin is a bacterial macrolide, marketed as sirolimus, that inhibits the mechanistic target of rapamycin (mTOR), the kinase complex through which cells decide whether conditions favour growth or conservation. It is one of the few compounds shown to extend lifespan in yeast, nematodes, flies and mice, and it is the most reproducible positive result in the US National Institute on Aging's Interventions Testing Program. Whether it does anything for human aging is unknown. The lifespan evidence comes from mice. A randomized lifespan trial in pet dogs has not reported, and no primate survival data have been published in a peer-reviewed journal. The human trials run so far have tested immune, body-composition and functional surrogates in small populations, and the one large randomized trial of a related compound failed its primary endpoint.

§How it works

mTOR sits at the centre of nutrient sensing. As part of complex 1 (mTORC1) it integrates amino-acid availability, growth-factor signalling and cellular energy state. When those inputs are favourable, it drives protein synthesis through S6 kinase and 4E-BP1, promotes ribosome biogenesis and suppresses Autophagy. Rapamycin does not bind mTOR directly. It first binds the small protein FKBP12, and the resulting complex docks onto mTORC1 and restricts its activity allosterically.

Inhibiting mTORC1 therefore shifts a cell from building to recycling. Autophagic flux rises, damaged organelles and aggregated proteins are degraded, and the burden on the protein quality-control system falls. Caloric restriction engages the same axis through diet, and that overlap is the main reason mTOR inhibition is treated as a pharmacological approximation of dietary restriction and not as an independent mechanism.

The complication is mTORC2. Acute rapamycin spares it, but chronic exposure disrupts its assembly in some tissues, and mTORC2 inhibition is associated with insulin resistance and glucose intolerance.¹ Much of the current interest in intermittent dosing, and in mTORC1-selective inhibitors built to leave complex 2 untouched, follows from this one pharmacological fact.

Why mTOR keeps appearing

Nearly every intervention that reliably extends lifespan in a model organism (dietary restriction, reduced growth-hormone signalling, several genetic mutants including the long-lived daf-2 nematodes) converges on reduced mTORC1 output and increased autophagy. Rapamycin is the most direct available way to hit that node with a drug.

§Development history

1. 1964
   Soil sample collected
   A Canadian medical expedition to Rapa Nui (Easter Island) collects soil that later yields Streptomyces hygroscopicus.
2. 1972
   Compound isolated
   Researchers at Ayerst in Montreal isolate an antifungal macrolide from the sample and name it rapamycin after the island.
3. 1991
   TOR genes identified
   Yeast mutants resistant to rapamycin reveal the TOR genes, opening the pathway to molecular study; the mammalian homologue follows in 1994.
4. 1999
   Approved as sirolimus
   The drug is approved in the United States to prevent rejection in kidney transplantation, establishing decades of human safety data at immunosuppressive doses.
5. 2009
   Lifespan extension in mice
   The Interventions Testing Program reports that rapamycin started at 600 days of age extends median and maximal lifespan in genetically heterogeneous mice of both sexes.
6. 2014
   Immune benefit in older adults
   The rapalog everolimus, given at low dose for six weeks, raises antibody response to influenza vaccination in older volunteers by about 20%.
7. 2017
   First dog trial
   A ten-week placebo-controlled pilot in 24 middle-aged companion dogs reports no clinical side effects and improved echocardiographic measures.
8. 2019
   Phase 3 failure
   resTORbio's RTB101, a TORC1 inhibitor distinct from rapamycin, does not reduce clinically symptomatic respiratory illness in adults 65 and older, and the company stops developing it for that indication.
9. 2024
   Dog trial refunded
   After the Dog Aging Project's main federal grant is not renewed, a separate NIH grant from December 2024 funds the TRIAD rapamycin trial through November 2029.
10. 2025
    PEARL results published
    The 48-week PEARL trial of weekly compounded rapamycin in healthy adults misses its primary endpoint, visceral fat, with improvements in a few secondary measures in subgroups.

§Evidence in animals

§Mice

The mouse result is unusually robust. In the ITP's 2009 study, genetically heterogeneous mice fed encapsulated rapamycin from 600 days of age, which the authors equate roughly to a 60-year-old person, lived longer at all three test sites. Age at 90% mortality, the study's measure of maximal lifespan, rose by 14% in females and 9% in males, and mean lifespan by 13% and 9%.² When later cohorts started at 9 months, the effect grew with dose. At 42 ppm, three times the original dose, median lifespan rose by 23% in males and 26% in females, and females gained more than males at every dose, which the authors suggested may reflect higher blood levels of the drug in females.³ A 2020 study starting at 20 months found that a schedule of one month on and one month off also extended survival in both sexes, though less than continuous dosing in females, while a single three-month course helped males only.⁴ The programme's methods and other results are covered under Interventions Testing Program.

Lifespan is not the same as Healthspan, and neither is the same as slower aging. In the 2009 study, treated mice died of the same pattern of diseases as controls.² Late-life treatment has improved some functions; three months of rapamycin in 24-month-old female mice reversed or attenuated age-related changes in heart function.⁵ But a broad phenotyping study in male mice found that rapamycin extended lifespan while improving few of the aging traits measured, and several of the traits it did change shifted in young mice too, which the authors read as drug effects unrelated to aging itself.⁶ Rapamycin does not produce the uniform rejuvenation across the Hallmarks of aging that popular accounts imply.

§Dogs

The first randomized dog study, a Dog Aging Project pilot published in 2017, gave 24 healthy middle-aged dogs a non-immunosuppressive dose of rapamycin or placebo for ten weeks. Treated dogs showed no clinical side effects compared with placebo, echocardiography suggested improvement in age-related measures of heart function, and mean red-cell volume fell.⁷ The pilot did not measure lifespan.

The decisive test is TRIAD, the Test of Rapamycin In Aging Dogs, a double-masked, placebo-controlled multicentre trial whose investigators describe it as the first rigorous test of a drug against biological aging, with lifespan and healthspan endpoints, outside the laboratory in any species.⁸ Its grant plans 580 companion dogs given 0.15 mg/kg of rapamycin or placebo once a week for one year and followed for two more. The first aim is lifespan and the incidence of age-related disease, and a second covers physical, neurological and cardiac function; 150 dogs were enrolled when the grant was written.⁹ The trial's completion was in doubt after the National Institute on Aging declined to renew the Dog Aging Project's main grant, as reported in January 2024,¹⁰ and a separate NIH award starting in December 2024 now funds it through November 2029.⁹ As of November 2026 TRIAD had not reported efficacy results, so there is not yet any dog evidence that rapamycin extends lifespan. A separate commercial effort, Loyal, is pursuing canine lifespan drugs with other mechanisms through the veterinary regulator.

§Non-human primates

Primate work has centred on the common marmoset, a small monkey short-lived enough for a survival study. In the first report, encapsulated rapamycin given orally at roughly 1 mg/kg a day produced trough blood levels averaging 5.2 ng/mL, which the authors placed within the therapeutic range for humans. Over 14 months they saw no clinical anaemia, lung fibrosis or mouth ulcers, and they described the drug as well tolerated.¹¹ Later reports from the same San Antonio group found only minor metabolic effects, with no significant change in glucose tolerance or blood lipids,¹² and only minor changes in blood counts after nine months of daily treatment in middle-aged animals.¹³

The tissue results are mixed. A 2026 study associated chronic treatment with partial preservation of salivary-gland structure and fewer senescent cells in the gland.¹⁴ A preprint found that treatment from about mid-life did not change age-related osteoarthritis severity on imaging but increased meniscus calcification, particularly in females.¹⁵ Epigenetic clocks built for marmosets detected no significant effect of rapamycin on the epigenetic age of blood.¹⁶

The group began a lifespan study and reported in 2019 that, more than three years into treatment, it was starting to assess longevity.¹⁷ In a 2024 radio interview the study's leader, Adam Salmon, said the treated animals were living longer and called it "the first non-human primate study showing a drug intervention-increased lifespan".¹⁸ As of November 2026 no survival data from the study had appeared in a peer-reviewed journal, so the claim cannot yet be assessed. No rhesus macaque lifespan result for rapamycin has been reported either.

§Human evidence

No trial has tested whether rapamycin changes how long people live or how long they stay healthy. The human evidence that exists falls into four groups.

The first is decades of transplant experience, which establishes the safety profile at immunosuppressive doses: stomatitis and mouth ulcers, raised blood lipids, impaired glucose handling, delayed wound healing, oedema and increased infection risk. Geroscience does not propose to use these doses.

The second is immune-function work at low or intermittent doses, mostly with drugs related to rapamycin. Six weeks of the rapalog everolimus raised influenza vaccine response in older volunteers by about 20%.¹⁹ In a 2018 phase 2a trial in 264 older adults, a low-dose combination of everolimus and the catalytic inhibitor BEZ235 was associated with fewer reported infections over the following year.²⁰ Those results gave the field its most cited paradox: a drug classed as an immunosuppressant appeared to improve some aspects of immune function in the old, plausibly by reducing the accumulation of exhausted and senescent lymphocytes that also drives Inflammaging.

A later developer, resTORbio, renamed BEZ235 as RTB101 and took it into larger trials. In a phase 2b trial of 652 participants, the first prespecified analysis, of RTB101 combined with everolimus, missed significance, while a second analysis pooling both parts found fewer laboratory-confirmed respiratory infections with 10 mg daily (19% of patients) than with placebo (28%). The phase 3 PROTECTOR 1 trial in 1,024 adults aged 65 and older then found no reduction in clinically symptomatic respiratory illness: 26% of patients on RTB101 had one, against 25% on placebo.²¹ The company announced the failure on 15 November 2019 and stopped developing the drug for that indication.²² RTB101 is not rapamycin, so the failure does not test rapamycin itself.

The third is the PEARL trial, run by the telemedicine company AgelessRx. Adults aged 50 to 85 received placebo or 5 mg or 10 mg of compounded rapamycin weekly for 48 weeks. Among the 114 who completed it, the primary outcome, visceral fat, did not change significantly, and adverse and serious adverse events were similar across groups. Lean tissue mass and self-reported pain improved in women on 10 mg, and self-reported emotional well-being and general health in the 5 mg group; no other effects were significant. Midway through, the investigators learned that the compounded drug might be poorly absorbed; it was later found to reach about a third of the blood concentration of the commercial formulation, the 10 mg group contained only eight women, and the authors were employees and shareholders of AgelessRx.²³

The fourth is a small trial of functional outcomes. In a 2026 exploratory trial, 40 sedentary adults aged 65 to 85 took 6 mg of sirolimus or placebo weekly for 13 weeks alongside home exercise. The drug did not improve the exercise gains, sensitivity analyses favoured placebo, and although 17 participants in each arm reported an adverse event, the sirolimus group had more events in total (99 against 63), including one possibly drug-related serious adverse event, a pneumonia.²⁴

Off-label use runs ahead of evidence

A minority of physicians prescribe rapamycin off-label for longevity, and a self-selected community of users takes it. In a 2023 survey of 333 adults with a history of off-label use, about nine in ten current users took it once a week, and mouth ulceration was the only condition reported significantly more often than by 172 non-users. The authors themselves note that self-reported data from a possibly self-selected group are less reliable than a randomized trial.²⁵ No dose, schedule or monitoring standard has been validated for healthy adults.

What the record does not show

Popular claims that drugs such as rapamycin can hold people at a fixed biological age go well beyond the evidence. In mice, the best-studied mammal, rapamycin lengthens life, but treated mice still die of the same pattern of diseases as untreated ones,² and in one broad study it improved few of the aging traits measured.⁶ The one dog lifespan trial has not reported, no primate survival result has been peer-reviewed, the marmoset clock analysis detected no significant change in epigenetic age, and no human trial has measured aging or lifespan as an outcome.

§Limitations

The question of dose and schedule is unresolved. Most animal lifespan data come from continuous dietary exposure, and the ITP's intermittent test alternated whole months on and off the drug.⁴ Most surveyed off-label users take a single weekly dose,²⁵ a schedule chosen largely by inference from mTORC2 pharmacology. Nobody knows whether the weekly pulse keeps the effect that continuous dosing produced in mice.

The endpoint question is harder still. No regulator accepts a measure of biological aging as a surrogate, so a trial would have to be powered on disease events over years. A shift in an Epigenetic clocks reading or in a composite age estimate is not evidence of clinical benefit. Rapamycin is also generic, so no company has a commercial reason to fund such a trial. The same structural problem has stalled the TAME trial, which Nir Barzilai has spent more than a decade trying to finance, and it is why the The longevity dividend remains an argument for research and not a description of an available drug.

§Outlook

Two lines of work could break the impasse. Bi-steric and other mTORC1-selective inhibitors, designed to leave complex 2 alone, would remove the metabolic penalty that limits chronic dosing and would test whether the metabolic side effects can be separated from the geroprotective effect. Narrow indications with measurable endpoints, among them vaccine response, periodontal disease, ovarian reserve and age-related cardiac decline, offer trials short enough to run and specific enough to interpret.

Until one of those produces a positive controlled result, rapamycin sits in an awkward position. It has the best animal evidence in geroscience and a plausible mechanism that converges with Senolytics and dietary restriction on shared damage pathways. It has nothing in humans that would justify recommending it to a healthy person over interventions with actual outcome data, starting with exercise.

§See also

• Autophagy
• Caloric restriction
• Dog Aging Project
• Interventions Testing Program
• Metformin and the TAME trial
• Senolytics
• Geroscience hypothesis
• Hallmarks of aging
• Healthspan
• The longevity dividend
• NAD+ precursors

§References