Rapamycin vs Metformin (for Longevity)

Mouse evidence

• Rapamycin: extends lifespan in three independent NIA-ITP sites, in both sexes, even with late-life initiation. The most reproducible pharmaceutical lifespan extension in mammals.
• Metformin: extends lifespan in some mouse studies, not others. ITP showed no significant lifespan effect at the tested doses.

Mechanism

Both act on conserved nutrient-sensing biology but at different nodes:

• Rapamycin: directly inhibits mTORC1 → reduced protein synthesis, raised autophagy, mitochondrial-quality maintenance.
• Metformin: inhibits mitochondrial complex I → raises AMP → activates AMPK → indirectly inhibits mTORC1 + other effects.

Rapamycin’s effect on mTORC1 is more direct and more potent.

Human evidence

• Rapamycin: PEARL trial showed modest body-composition / function benefit in healthy older adults. MANNICK trials showed improved vaccine response. Off-label use in private medicine is common but poorly characterised.
• Metformin: massive T2D evidence base (DPP, UKPDS, others). For non-diabetic longevity use, evidence is observational only. TAME remains in funding limbo.

Side effects

• Rapamycin: stomatitis, dyslipidaemia, hyperglycaemia, infection risk, impaired wound healing, rare pneumonitis. Major CYP3A4 drug interactions.
• Metformin: GI upset (frequent, often improves), B12 deficiency (~20% chronic users), lactic acidosis (rare but serious, especially in renal impairment).

The exercise-interaction question

A series of studies has suggested metformin blunts cardiometabolic adaptations to exercise in older adults — potentially the opposite of what longevity-minded users want. This has shifted some public voices (notably Peter Attia) from earlier metformin advocacy toward caution.

Rapamycin’s exercise interaction is less studied; some data suggest mTORC1 inhibition may blunt the hypertrophic response to resistance training.

Who is considering which

Profile	Rapamycin	Metformin
T2D or pre-diabetic	Probably not	Yes, evidence-based
Healthy adult, longevity-curious	Off-label, small trials	Off-label, weaker case
Concerned about cancer risk	Sometimes considered (mTOR inhibition)	Mostly observational signal
Heavy resistance training	Some concern	Some concern (exercise interaction)
On many other medications	CYP3A4 interactions matter	Generally cleaner

Combining them

Some longevity-clinic protocols combine the two. There is no human RCT data on the combination, and they have additive side-effect risks (GI, glucose, lactic-acidosis concern).

Related entries

Rapamycin, Metformin, mTOR, AMPK, PEARL, TAME, ITP.