Weekly rapamycin did not enhance exercise gains in older adults and may even have limited overall functional improvements.
Exercise is one of the most effective ways to preserve physical function with age, but researchers are also testing whether drugs that target aging-related pathways can complement the body's adaptations to exercise. An exploratory trial tested whether sirolimus, also called rapamycin, could be timed around exercise in a way that supports function in older adults.
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The study was a randomized, double-blind, placebo-controlled trial in 40 sedentary adults aged 65 to 85. Participants completed a 13-week home exercise program involving stationary cycling and chair stands (repeated sit-to-stand movements from a chair performed for 30 seconds) three times per week. They were assigned to receive either sirolimus, 6 milligrams once weekly, or a matched placebo, with the dose taken about 24 hours after the final weekly exercise session. Researchers measured chair-stand performance as the main outcome, along with grip strength, 6-minute walk distance, quality of life, C-reactive protein (CRP, a marker of inflammation), DNA methylation-based epigenetic age measures (estimates of biological age based on chemical tags on DNA), routine blood tests to monitor organ function, and adverse events.
- Both groups improved on the 30-second chair-stand test, but the sirolimus group tended to improve less, by about 2 fewer repetitions on average compared with placebo. This difference was too small and uncertain in the main analysis to know if it was real or just due to chance.
- In follow-up analyses that focused on participants who completed the study or closely followed the protocol, the gap became clearer. The sirolimus group performed about 2.5 to 3.4 fewer chair stands than the placebo group, and these differences clearly favored placebo.
- Other measures of physical function showed a similar pattern, with small differences favoring placebo, but none were strong enough to show a clear effect between groups. Grip strength was about 1.19 kg lower and walking distance about 4.87 meters shorter in the sirolimus group, while physical and mental quality-of-life scores also showed small differences.
- CRP did not show a consistent effect, and also the epigenetic age measures showed mixed results without a clear pattern.
- At least one adverse event was reported by 85% of participants in both groups. Even so, the sirolimus group had more adverse events overall (99 vs. 63), and more events the study team rated as possibly or probably treatment-related (35% vs. 15%).
Sirolimus has drawn interest in aging research because it inhibits mTORC1, one branch of the broader mTOR signaling network involved in nutrient and growth signaling. Constant high activity of mTORC1 signaling has been linked to shorter lifespan in animal studies, while more balanced activity is associated with better metabolic health. mTORC1 also plays an important role in muscle repair and adaptation after exercise, which creates a tension: suppressing it might support some aging-related processes while potentially interfering with training gains. This trial tested a timing strategy meant to separate these effects by spacing sirolimus away from the main post-exercise recovery and apdaption window. However, the findings suggest that the drug's long half-life may have allowed mTORC1 inhibition to persist into the next training sessions, potentially dampening the beneficial effects of exercise on physical function.
The main limitation is that this was a small, short trial, so the results are best viewed as an early signal rather than a final answer. Still, the findings suggest that weekly sirolimus may not pair well with exercise at this dose and schedule. In Q&A #40, I discuss potential longevity-related benefits and trade-offs of rapamycin.