Can Two Old Drugs Slow Aging?

Both of these are established, approved drugs — rapamycin for organ transplant immunosuppression, metformin for type 2 diabetes — being repurposed and studied specifically for longevity, with different evidence tiers behind each.

Rapamycin: The Most Robust Animal Longevity Drug, With Real Human Uncertainty

Rapamycin fed to genetically diverse mice late in life extended both median and maximum lifespan by roughly 9–14%, depending on sex, at a dose that substantially inhibited mTOR signalling — in a landmark study run through the National Institute on Aging's multi-site Interventions Testing Program[6], directly connecting back to the mTOR pathway covered in Section 4. This remains among the most robust, best-replicated lifespan-extension findings in mammalian aging research. The caveat: no equivalent human lifespan trial exists. Some physicians prescribe it off-label for longevity based on the strength of the animal data, but rapamycin carries real risks, including immune suppression, given its origin as a transplant-rejection drug — this is not a drug to self-prescribe. General guidance on evaluating off-label drug use with a doctor is covered in the Medication Literacy guide.

Metformin: Strong Observational Signal, Trials Still Developing

A systematic review and meta-analysis of observational studies found that diabetics taking metformin had lower all-cause mortality not just than diabetics on other treatments, but slightly lower than non-diabetics in the general population — a striking, if observational, signal[7]. This is interesting precisely because it suggests an effect beyond simple diabetes control. It's also, definitionally, observational data — subject to the same causality caveats as any large cohort comparison, since people prescribed metformin differ from the general population in ways beyond just their diabetes status. Large, purpose-built trials testing metformin specifically for aging-related outcomes in non-diabetics are underway but not yet complete as of this guide's writing, so the current position is: a promising observational signal, not yet confirmed by the kind of trial that would move it to Tier 1 or 2.

A Trade-off Worth Knowing

Both drugs interact with the mTOR/AMPK system covered in Section 4, which raises a practical question for anyone combining either with serious resistance training: some evidence suggests metformin may partially blunt the muscle-adaptation response to resistance training, since that adaptation depends partly on mTOR activation that metformin's AMPK-activating mechanism can work against. A practical sign to watch for: strength gains coming in slower than expected while on metformin and training consistently. Unresolved — talk to a physician before combining.