Issue #23 mTOR inhibition B April 18, 2026

Rapamycin: the longevity drug
hiding in plain sight

How an antifungal from Easter Island became the most credible life-extension molecule in geroscience — and what the human data actually shows.

Editor's note

Rapamycin has been approved by the FDA since 1999 — as an immunosuppressant for organ transplant recipients. But over the past decade, a quiet consensus has been building among longevity researchers: at lower, pulsed doses, it may do the opposite of suppress your immune system. This issue, we go deep on the mechanism, the human data we do and don't have, and how people are actually using it off-label today.

Standard caveat: nothing here is medical advice. This is a research newsletter. You are responsible for your own decisions.

Mechanism

What mTOR inhibition actually does

mTOR (mechanistic target of rapamycin) is a nutrient-sensing kinase that acts as a master growth switch. When active, it tells cells to build — synthesize proteins, grow, divide. When suppressed, cells shift into maintenance mode: recycling damaged components via autophagy, slowing the hallmarks of cellular aging.

The longevity hypothesis is that chronic mTOR hyperactivation is pro-aging. Pulsed rapamycin — dosed weekly rather than daily — inhibits mTORC1 while largely sparing mTORC2, which governs immune function and metabolic regulation. This is why pulse dosing matters.

Key distinction

Daily rapamycin (transplant dosing) → immunosuppression, metabolic side effects. Weekly pulsed rapamycin (longevity dosing, 1–8mg) → mTORC1 inhibition with mTORC2 largely intact. Different drug, different dose, different goal.

Dosing landscape

How people are actually dosing it

Parameter	Low	Moderate	High	Notes
Weekly dose	1–2 mg	3–5 mg	6–10 mg	Most longevity physicians start here
Frequency	Every 10–14 days	Weekly	Weekly	Weekly pulse preferred over daily
Duration	Trial 3 mo	Ongoing	Ongoing	Re-assess lipids at 90 days
With food	Yes	Yes or fasted	Fasted	High-fat meal ↑ absorption ~34%

⚠ These are observational community ranges, not clinical recommendations.

Evidence review

What the literature says

Tiered S–F. S = consistent, well-powered human RCT; A/B = strong human data with caveats; C = mixed or animal-heavy; D/F = thin or conflicting.

Mannick et al. 2014 — Everolimus enhances immune response to flu vaccine in elderly (n=218 RCT)

n=218 · Human RCT

mTOR inhibition at low dose enhanced, rather than suppressed, immune response in elderly subjects — directly challenging the immunosuppression narrative.

Mannick et al. 2018 — RTB101 (mTORC1 inhibitor) reduces respiratory tract infections in elderly

n=652 · Human RCT

Statistically significant reduction in RTIs. Supported the idea that partial mTOR inhibition is distinct from full immunosuppression.

Kaeberlein lab cohort — longevity physician survey, n=333 patients on weekly rapamycin

n=333 · Observational

Majority reported no serious adverse effects at 1–6mg/week. Lipid changes (↑LDL) in ~30% warranted monitoring. No controls.

ITP study — Rapamycin extends median lifespan 9–14% in genetically heterogeneous mice

n=~1800 mice · Animal RCT

Replicated across 3 independent labs. Starting late in life (20 months) still effective. Most robust longevity data in any mammal to date.

Case series: ulcerative oral lesions at >5mg/week

n=12 cases · Case series

Mouth sores are the most common reported side effect at higher doses. Usually resolves on dose reduction. Grade D — no controls, unclear causal attribution.

Before you consider this

Contraindications & monitoring

Avoid if

– Active infection

– Pregnancy or planning

– Immunocompromised baseline

– Concurrent CYP3A4 inhibitors (azoles, grapefruit)

Monitor at baseline + 90d

– Fasting lipid panel

– CBC (WBC/platelets)

– HbA1c / fasting glucose

– CMP (liver enzymes)

Drug interactions

– Cyclosporine (↑ rapa levels ×3)

– Diltiazem / verapamil

– Strong CYP3A4 inducers (rifampin)

– St. John's Wort

Bottom line

Our read

Rapamycin is the most compelling longevity compound we're aware of — it's the only thing that robustly extends lifespan across multiple mammalian models. The human immune data is genuinely encouraging. But we're still waiting on a dedicated human longevity RCT.

The people taking it are mostly doing so under physician supervision, with lipid monitoring. The side-effect profile at pulsed low doses appears manageable. We rate this Grade B — not because the mechanism is weak, but because we don't yet have the long-term human lifespan data. That study is effectively ongoing, in the community of people taking it now.