Longevity · 9 min read · Published September 8, 2026

The Rapamycin Dosing Debate: What PEARL Tested, the Bioavailability Problem, and What Is Unproven

An educational review of the human rapamycin evidence: the 48-week PEARL trial (Aging, 2025), the finding that compounded rapamycin delivers about 31 percent of the blood level of commercial tablets, the 333-person user survey, Blagosklonny's case for weekly schedules, the mouse lifespan data, and why no human lifespan benefit has been shown.

Does rapamycin extend human lifespan?

Not as far as anyone has shown. Rapamycin extends median lifespan in mice by 9 to 26 percent depending on dose and sex (ITP, 2009 and 2014). The only randomized human longevity trial, PEARL (n=114, 48 weeks, published 2025), measured safety and body composition, not survival. As of September 2026 there is no human lifespan data; longevity use is off-label.

Rapamycin is an FDA-approved prescription drug (Rapamune, sirolimus) with labeled uses in kidney transplant rejection and lymphangioleiomyomatosis. It is not approved for aging, and every schedule discussed below is either a trial parameter or an opinion. That framing matters because rapamycin is probably the most-argued-about molecule in longevity: it has the best animal lifespan data of any drug, a loud community of self-experimenters, and a human evidence base that fits in one article. This is that article.

What did the PEARL trial actually test?

PEARL (NCT04488601) randomized healthy adults to placebo, 5 mg or 10 mg of compounded rapamycin once weekly for 48 weeks; 114 completed (39 placebo, 40 on 5 mg, 35 on 10 mg). Published in Aging in April 2025, it found no change in visceral fat, adverse events comparable to placebo, and a lean mass gain in women on 10 mg.

PEARL (Participatory Evaluation of Aging and Rapamycin for Longevity) was a decentralized, double-blind, placebo-controlled trial crowdfunded largely through Lifespan.io and run by AgelessRx, a telehealth company that prescribes rapamycin; seven authors are its employees and shareholders, which the paper discloses. That is unusual and worth knowing. The published paper reports the pre-specified primary outcome, visceral adiposity by DXA scan, as unchanged across groups (p = 0.94). Serious adverse events were 1 in the 10 mg group, 2 in the 5 mg group and 3 on placebo. Non-serious events were also similar, with one exception: gastrointestinal symptoms were reported by 8 people on 10 mg, 7 on 5 mg and 4 on placebo.

The lean mass result is the one that gets quoted. It is a subgroup finding (women, top arm) in a trial of 114 people, which is the kind of result that needs replication before it means anything, and the authors say so. The result that should get quoted more is the null primary outcome: a year of weekly rapamycin did not move visceral fat, the endpoint the investigators chose in advance.

Why is compounded rapamycin only about 31 percent bioavailable?

A GeroScience 2025 study measured blood rapamycin 24 hours after dosing in 44 people on commercial tablets (2, 3, 6 or 8 mg) and 23 on compounded capsules (5, 10 or 15 mg). Compounded rapamycin produced 0.27 ng/mL per milligram versus 0.87 for commercial, about 31 percent, which the authors attribute to formulation differences.

This finding, from the same research group that ran PEARL, reframes the trial. PEARL used compounded rapamycin, and the bioavailability paper states that the compounded product reached roughly one third of the blood concentration of the commercial one. In blood-level terms, PEARL's 10 mg arm behaved more like 3 mg of the branded drug, and the 5 mg arm like less than 2 mg. That may explain the clean safety profile as much as any property of weekly scheduling, and it makes 'X mg weekly' claims from different sources non-comparable unless the formulation is named. The paper also extended the analysis to 316 users in an observational database and reported that blood levels peaked around day 2 and declined gradually, consistent with the drug's long half-life.

What does the 333-person user survey show?

A 2023 GeroScience survey (Kaeberlein et al.) collected self-reports from 333 off-label rapamycin users and 172 non-users. About 9 in 10 users took it once weekly, roughly 20 percent without a physician, and mouth ulcers were the only side effect significantly more common in users. A 2024 follow-up found 26 percent reported oral changes, mostly transient sores.

The survey is the largest description of real-world longevity use and it is honest about its limits: respondents self-selected, people who quit because of side effects were less likely to answer, and users rated themselves better on health, happiness and brain function by ratios above 3 to 1, which is exactly what you would expect from people who chose to keep taking something. The oral health follow-up found that the frequency of mouth ulcers was not related to dose, interval or duration, and that severe ulcers were rare. Several authors of both survey papers are employees or shareholders of AgelessRx, the company that ran PEARL, which the papers disclose.

Why weekly? Blagosklonny's reasoning

Mikhail Blagosklonny's 2019 opinion article in Aging argued that intermittent, higher-peak dosing could inhibit mTORC1 for the anti-aging effect while sparing mTORC2, whose chronic inhibition is linked to insulin resistance, and that a drug-free interval would let stem cells regenerate. It is a mechanistic hypothesis; no trial has compared schedules for aging outcomes.

The article is the intellectual source of nearly every weekly schedule in use. Its logic: daily rapamycin in transplant patients produces the familiar side effects (mouth sores, raised lipids, glucose intolerance, slowed wound healing) partly through prolonged mTORC2 inhibition, and a pulse schedule that keeps the same total dose but lengthens the interval might keep the benefit and lose the cost. Blagosklonny also argued that rapamycin should be started before disease rather than after. Readers should hold two things at once: this reasoning is coherent and widely accepted in the field, and it has never been tested against a daily schedule in a human aging trial. He himself framed human life extension as a prediction from mouse data, not a demonstrated fact.

What the mouse data show, and what they do not

The mouse evidence is the reason anyone takes this drug. In 2009 the NIA Interventions Testing Program reported in Nature that rapamycin at 14 ppm in food, started at 600 days of age (roughly 60 in human years), extended lifespan in genetically heterogeneous mice at three independent sites, with an increase of 14 percent in females and 9 percent in males at the 90th percentile of survival. In 2014 the same program, in Aging Cell, tested a threefold higher dose of 42 ppm and found median lifespan up 23 percent in males and 26 percent in females, with a larger effect in females at every dose, possibly because female mice reach higher blood levels. It is the only drug the ITP has found to extend mouse lifespan robustly and repeatedly.

What the mouse data cannot tell you: whether a weekly human schedule at a fraction of the mouse exposure does anything to human aging; whether the mouse benefit, which comes partly from postponing cancer deaths, transfers to a species with a different cancer profile; and whether lean mass in 35 women over a year is a proxy for anything. The human trial that would answer the lifespan question would need thousands of people and decades, and nobody has funded one. Evidence tiers, then: animal lifespan, strong and replicated; human safety over one year, moderate; human aging outcomes, none.

The bottom line

The rapamycin debate is often framed as 'what dose', and the honest answer is that the human trials so far were designed to ask 'is it safe for a year' and got a reassuring answer with a compounded product that delivered a third of the expected drug. Whether any schedule slows human aging is unproven in September 2026. Rapamycin is a prescription immunosuppressant, and its off-label use is a decision for a physician and patient with the trial parameters above in front of them.