Rapamycin (Sirolimus)

Mechanism of Action

Rapamycin (sirolimus) is a macrolide compound produced by the bacterium Streptomyces hygroscopicus. It binds to the intracellular protein FKBP12, forming a complex that directly inhibits mTOR Complex 1 (mTORC1) — the master regulator of cell growth, protein synthesis, and one of the most upstream controllers of the ageing process.

mTORC1 integrates signals from nutrients (amino acids, glucose), growth factors (insulin, IGF-1), and cellular energy status. When chronically overactivated — as occurs in modern, calorically-abundant environments — mTORC1 drives the hallmarks of ageing:

• Suppressed autophagy — cellular waste accumulates
• Impaired proteostasis — damaged proteins aggregate
• Stem cell exhaustion — regenerative capacity declines
• Senescent cell accumulation — SASP drives systemic inflammation

By pulsed inhibition of mTORC1, rapamycin reactivates autophagy, improves proteostasis, and appears to partially reset immune ageing.

Human and Animal Evidence

Lifespan extension across organisms: Rapamycin extends lifespan in yeast, worms, flies, and mice — representing four independent evolutionary lineages. The ITP (Interventions Testing Programme) found median lifespan extension of 9–14% in genetically heterogeneous mice when started at 20 months (equivalent to age 60 in humans). ^[]

Immune rejuvenation (TORC1 inhibition): A landmark 2014 study by Novartis showed that a rapamycin analogue (everolimus) improved influenza vaccine response in elderly humans by ~20% — the first direct evidence of immune rejuvenation in humans. ^[]

Cardiac function: Rapamycin reversed age-related cardiac hypertrophy and improved diastolic function in aged mice even when started late in life — suggesting reversibility of some ageing phenotypes. ^[]

Ongoing human trials: The PEARL trial (Phase 2 RCT, 2024–2026) is evaluating 5mg/week rapamycin vs. placebo in healthy adults aged 50–85 across multiple biological age clocks. Results expected 2026–2027.

Weekly Pulsed Dosing Rationale

Continuous rapamycin dosing (as used in transplant patients at 2–5mg/day) causes significant immunosuppression and metabolic side effects. Longevity protocols use once-weekly pulsed dosing (typically 3–10mg) to achieve mTORC1 inhibition while allowing mTORC2 recovery.

mTORC2 — which rapamycin does not directly inhibit acutely but affects with chronic dosing — regulates glucose homeostasis, cell survival, and cytoskeletal organisation. Weekly pulsing appears to preserve mTORC2 function while still delivering longevity benefits.

Practical Usage Notes

Start at 1mg/week for 4 weeks to assess tolerance, then titrate to 3–6mg/week. Blood levels (trough rapamycin) can be measured 24h post-dose; most longevity physicians target 3–8 ng/ml. Lipid panel and fasting glucose should be monitored quarterly. Avoid during any active infection or planned surgery (pause 2–3 weeks pre-operatively).

⚕ Prescription Required. Rapamycin is a prescription medication in all major jurisdictions. This profile is for educational purposes only. Obtain via a qualified longevity physician who can monitor blood levels and manage interactions.