PEARL rapamycin trial results: safe over a year, primary endpoint unmoved

Rapamycin is the most consistently life-extending drug in laboratory rodents, and a growing number of adults take it off-label in the hope that the effect carries over. The PEARL trial is the evidence most often cited for that hope. It is worth reading carefully, because what it establishes and what it is quoted for are two different things.

PEARL — Participatory Evaluation of Aging with Rapamycin for Longevity — was a 48-week, decentralised, double-blind, placebo-controlled trial in healthy adults aged 50 to 85, registered as NCT04488601 [s1]. Participants took placebo, 5 mg or 10 mg of compounded rapamycin once weekly. Its authors describe it as the longest clinical study of rapamycin for healthy ageing performed to date [s1]. All seven are employees and shareholders of AgelessRx, the telehealth company that ran it [s1].

The primary endpoint did not move

PEARL's pre-specified primary outcome was change in visceral adipose tissue, measured by DXA scan. It did not change significantly across the dose groups: partial eta squared of 0.001, p = 0.942 [s1]. Blood biomarkers stayed within normal ranges [s1].

That is the finding a reader should carry away first. A trial's primary endpoint is the question it was designed and powered to answer, and PEARL's answer was no.

What it did establish: tolerability

The safety result is the trial's real contribution. A total of 114 participants completed the study and were analysed — 40 on 5 mg, 35 on 10 mg and 39 on placebo — with a further 11 discontinuing before completion and excluded from the analysis [s1]. Non-serious adverse events were near-identical across arms: 117 in the 10 mg group, 116 in the 5 mg group and 122 on placebo [s1]. Serious adverse events were rare and, if anything, skewed the other way: one in the 10 mg group, two in the 5 mg group and three on placebo [s1]. Gastrointestinal symptoms were the one signal that separated the groups, reported by 8, 7 and 4 participants respectively [s1].

Immune suppression is the standard concern with rapamycin, and the trial looked for it. Reports of cold and flu-like illness and slowed recovery were similar across all groups [s1]. There was a single case of anaemia across the whole study, in a participant taking 5 mg, which resolved after transfusion [s1].

The positive findings, and how thin they are

PEARL is usually cited for improvements in lean tissue mass and self-reported pain in women. Both are secondary or exploratory outcomes, and both come from a very small subgroup.

Women made up 35.1% of the cohort — and only 20% of the 10 mg group, which is eight people [s1]. It is in those eight that the lean-tissue effect sits. The odds ratio for improvement in lean tissue mass among women on 10 mg was 28, with a 95% confidence interval running from 2.42 to 323.7 [s1]. A confidence interval spanning two orders of magnitude is what an estimate looks like when it is built on almost no data. The corresponding mean difference against placebo at 48 weeks was 6.194, with an interval of 0.8773 to 11.5105 [s1].

Self-reported pain on the SF-36 improved for women, by a mean of 8.071 points at 48 weeks (95% CI 3.044 to 13.098) [s1]. Emotional well-being improved in the 5 mg group — and also, significantly, in the placebo group, by a mean of 4.267 points [s1]. The trial's own abstract attributes the emotional well-being improvement to 5 mg rapamycin without noting that placebo improved too [s1]. Readers who stop at the abstract will draw a stronger conclusion than the results section supports.

Where the trial did measure ageing biology directly, it found nothing. Epigenetic age testing was run on a subset of 24 participants and showed no meaningful significant changes between groups [s1]. The gut microbiome analysis found a small but significant increase in dysbiosis in men taking 10 mg [s1].

The dose the trial actually tested is not the dose on the label

Midway through, the investigators learned that the compounded rapamycin they were using has roughly one-third the blood concentration at 24 hours of commercial formulations [s1]. A companion study of real-world users confirmed that compounded rapamycin yields a lower blood level per milligram than the commercial product [s3]. They paused the trial to check, confirmed it, and reported that the equivalent effective doses were about 66% lower than the advertised numbers — the 10 mg compounded arm corresponds to roughly 3.33 mg of generic sirolimus [s1].

This cuts both ways. The reassuring safety record belongs to a lower exposure than "10 mg weekly" implies, and so does the absence of efficacy. Anyone reading PEARL as evidence about a particular milligram figure is reading it wrong in both directions.

Where this leaves the evidence

A review published later in 2025 in the same journal surveyed the whole body of low-dose rapamycin and rapalog research in healthy adults and counted fewer than a dozen trials [s2]. Its conclusion was that despite the preclinical evidence, human data have yet to establish that rapamycin or its analogues can delay ageing in healthy older adults [s2].

PEARL is consistent with that. It shows that a year of low-dose intermittent rapamycin in health-conscious middle-aged and older adults produced no more adverse events than placebo, no change in the outcome it was built to measure, and scattered secondary signals in subgroups too small to settle anything. The investigators say as much: findings are limited by small cohort size and require replication and extension before conclusions can be drawn [s1].

The next test is a much larger one. Rapamycin is generic, which means no company has a commercial reason to fund the trial that would settle the question [s2] — a structural problem the field has not solved.

Rapamycin is a prescription immunosuppressant. Nothing here is a recommendation to take it, and no dose in this article should be read as guidance.

Sources

1. [s1] Influence of rapamycin on safety and healthspan metrics after one year: PEARL trial results. Aging (Albany NY), published online April 4, 2025. https://doi.org/10.18632/aging.206235
2. [s2] What is the clinical evidence to support off-label rapamycin therapy in healthy adults? Aging (Albany NY), published online August 7, 2025. https://doi.org/10.18632/aging.206300
3. [s3] The bioavailability and blood levels of low-dose rapamycin for longevity in real-world cohorts of normative aging individuals. GeroScience, published online January 28, 2025. https://doi.org/10.1007/s11357-025-01532-w