The PEARL rapamycin trial, two years on

The Participatory Evaluation of Aging with Rapamycin for Longevity (PEARL) trial finished its primary 48-week endpoint in 2023 with a result that disappointed the rapamycin community: no statistically significant change in lean mass, no change in pain scores, and a non-significant signal on visceral fat. The headline reading at the time was that rapamycin in healthy adults at 5–10 mg per week does not move the needle. The 24-month follow-up paper, published in Aging Cell in early 2026, complicates that reading in three useful ways.

What the follow-up actually reports

First, the inflammatory readouts that did move at 48 weeks moved further at 24 months. Hs-CRP fell by a median of 18% in the 10 mg/week arm; IL-6 fell by 14%. These are modest absolute changes but they are durable, and they replicate the direction of effect seen in the much smaller 2014 RAD001 study. Second, the previously non-significant lean-mass signal in the 5 mg arm became statistically significant in the female subgroup at 24 months — a finding the authors are appropriately cautious about, given the subgroup was not pre-specified. Third, and most usefully for clinicians, the trial reports a clean dose-response in adverse-event rate: oral aphthous ulcers rose from 4% in placebo to 11% at 5 mg and 23% at 10 mg, with no other treatment-emergent adverse event reaching pre-specified concern thresholds.

The two interpretations that are both wrong

The optimistic misreading is: PEARL works, the 48-week paper just measured the wrong endpoints. The pessimistic misreading is: PEARL doesn't work, the 24-month paper is a fishing expedition. Both readings ignore what the trial was actually designed to test, which was whether intermittent rapamycin produces measurable functional benefit in healthy older adults at doses that avoid the metabolic side effects seen in transplant medicine. The honest answer at 24 months is: yes, on inflammatory endpoints; probably, on lean mass in women; not yet on subjective function; and at a tolerability cost that is real but manageable.

Who benefited, and who didn't

The most clinically actionable finding in the follow-up is the responder analysis. Participants in the top quartile of baseline hs-CRP — i.e. the most inflamed at trial entry — showed roughly twice the absolute reduction in inflammatory markers as the cohort average. Participants in the bottom quartile of baseline hs-CRP showed essentially no change. This is consistent with a regression-to-mean concern, but it is also consistent with the pharmacological intuition that mTOR inhibition matters most when mTOR signalling is elevated in the first place.

A practical reading: rapamycin probably helps the inflamed, sedentary, metabolically uneven adult more than it helps the lean, well-trained, well-slept one. The latter cohort already has tonically lower mTORC1 activity through behavioural means; pharmacological inhibition adds little.

If we had to pick one phrase to summarise PEARL at 24 months, it would be: rapamycin tilts the inflammatory baseline of the people whose inflammatory baseline is tilted to begin with. That is not nothing. It is also not the dramatic geroprotection some of the early framing implied.

What the trial cannot tell us

• Whether the inflammatory benefit translates to hard endpoints (incident cardiovascular events, incident dementia). The trial is far too small and far too short to address this.
• Whether the female-specific lean mass signal is real or a multiple-testing artefact. A pre-specified replication is needed.
• Whether 5 mg and 10 mg per week represent the optimal dose range, or whether higher monthly pulses (e.g. 20 mg every 2 weeks) would deliver the same benefit with fewer aphthous ulcers.
• Whether co-administration with metformin, the most common adjunct in clinical practice, alters the effect size.

How we update the protocol

Vitaei's clinician panel updated its rapamycin entry on the day the follow-up was published. The change was modest. We continue to recommend a starting dose of 5 mg weekly for adults over 50 with elevated hs-CRP who have completed a baseline metabolic and infectious-disease workup; we continue to advise against unsupervised use in adults under 40 outside a clinical trial; we now explicitly note the female lean-mass signal as exploratory but suggestive; and we have reduced the strength of our caution on aphthous ulcers from "common, often dose-limiting" to "common, generally tolerable, dose-responsive."