mTOR (mechanistic target of rapamycin) is a cellular pathway that senses nutrient availability and governs a basic tradeoff every cell makes: growth and reproduction versus maintenance and repair. Inhibiting mTOR shifts cells toward the maintenance side of that tradeoff, and doing so with rapamycin, originally developed as an organ-transplant immunosuppressant, is one of the most replicated lifespan-extension interventions in science, effective across yeast, worms, flies, and mice.
That cross-species consistency is unusually strong for aging research, which is why mTOR inhibition is often cited alongside caloric restriction as one of the best-established levers for slowing aging in animal models. The open question is translation: rapamycin's original use as a full-dose immunosuppressant carries real side effects, and human aging trials use much lower, intermittent dosing specifically to try to capture the geroprotective effect while avoiding immune suppression. Results from human geroscience trials, including work associated with the PEARL trial, are still accumulating.
This entry connects directly to the gene therapy entry in this directory, which covers mTOR signaling as a genetic-intervention target; rapamycin represents the pharmacological route to the same pathway rather than a genetic one, and is far further along in terms of real-world human use given its decades of prior clinical history in transplant medicine.