All available studies have been conducted in people with type 2 diabetes, and the results are contradictory. The TAME trial, which is intended to test this in healthy people, has not yet produced results. In addition, multiple independent studies indicate that metformin can noticeably blunt the muscle and fitness gains from exercise, which is a concrete drawback.
Metformin has been on the radar for years as a potential anti-ageing agent, but at this point there is not a single completed study in healthy people demonstrating that it extends lifespan or healthy years. The studies that do exist were conducted almost entirely in people with type 2 diabetes, and even there the outcomes contradict each other: an early signal suggesting that metformin might allow diabetics to outlive healthy people without diabetes was not confirmed in a larger, more recent analysis.
The large trial that should properly test this, the TAME trial, has so far never got off the ground due to a lack of funding. There are therefore no results, and the claim that metformin produces a proven extension of lifespan in healthy people remains unsubstantiated. What is well documented, however, is that the drug can noticeably blunt the muscle and fitness gains you would normally get from strength training or endurance sports. Three independent studies point in the same direction, including a 2025 study in older adults with muscle weakness. If exercise is a cornerstone of your strategy, that drawback carries considerable weight.
As a prescription treatment for diabetes it is well studied and generally safe. Side effects include gastrointestinal complaints and, with prolonged use, sometimes a vitamin B12 deficiency. It is, however, a prescription-only medicine, and without a diabetes diagnosis you cannot simply pick it up at a pharmacy in the Netherlands. A doctor who prescribes it purely as an anti-ageing agent is prescribing it off-label, without the effectiveness for that purpose having been demonstrated.
If you take the longevity angle seriously, the honest conclusion is that the evidence here is simply still lacking, while the possible downside for your muscle mass and fitness is meanwhile quite concrete. If you would like to know which lifestyle interventions do have solid backing for your specific situation, I can elaborate on that.
Limited evidence, 7 source(s); treat with caution.