Metformin
Glucophage, dimethylbiguanide
One of the most prescribed drugs on earth, with sixty years of safety data and a longevity reputation resting on a trial that has still never been funded.
FDA-approved
FDA-approved for type 2 diabetes and first-line in essentially every treatment guideline. Widely prescribed off-label for prediabetes and polycystic ovary syndrome. No approval anywhere for ageing.
What it is
Metformin is a biguanide derived from a compound in French lilac, in clinical use since the 1950s and first-line therapy for type 2 diabetes worldwide. Its primary action is reducing hepatic glucose production, with secondary effects on insulin sensitivity, partly through AMPK activation and partly through mechanisms still being argued about.
For diabetes it is uncontroversial, cheap, and extremely well characterised. Everything interesting about it on this site concerns the other claim.
Where the longevity reputation came from
Observational studies reported that people with diabetes taking metformin had mortality rates comparable to, and in some analyses better than, matched people without diabetes. That is a striking finding and it launched a decade of interest.
It is also the kind of finding that observational data produces and then fails to confirm. Metformin is prescribed to healthier diabetic patients; sicker ones are moved to insulin. That is confounding by indication, and it is exactly the pattern that generates spurious survival advantages.
The trial that would answer it does not exist
TAME, Targeting Aging with Metformin, was designed specifically to test whether metformin delays age-related disease in non-diabetic older adults. It has been discussed since 2015. It has never been fully funded and has never run.
That is the single most important fact for anyone weighing this compound for longevity. The definitive trial was designed, the field agreed it was the right trial, and it has not happened. In the meantime the evidence base consists of observational data, mechanistic work, and small randomised trials with surrogate endpoints such as the recent 24-week study reporting increased leukocyte telomere length in prediabetes.
Surrogate endpoints are not lifespan. Telomere length in white blood cells is a marker whose relationship to healthy ageing remains contested.
The exercise problem
Several studies have found that metformin blunts the adaptations to aerobic and resistance training, including mitochondrial adaptations and gains in insulin sensitivity from exercise itself.
The findings are not unanimous, but the direction is consistent enough to matter. If the mechanism of benefit is partly AMPK activation, and exercise activates AMPK, then taking a drug that occupies the same pathway may be substituting for the intervention with far better evidence rather than adding to it.
Practical notes
- Check B12. Long-term metformin depletes it, the deficiency presents neurologically, and it is easy to miss and easy to test.
- Extended-release is worth asking for. Most of the gastrointestinal intolerance that makes people abandon the drug is a formulation problem.
- Lactic acidosis is rare and real. The risk concentrates in people with impaired renal function, dehydration or acute illness, which is why the rules about stopping it around contrast imaging and acute illness exist.
- For a healthy person, the honest summary is that the case is unproven and the trial was never run. That is a very different position from the mouse-level evidence behind rapamycin.
Side effects and warning signs
Commonly reported
- Diarrhoea and abdominal discomfort, common at initiation and the main reason people stop
- Nausea and metallic taste
- Vitamin B12 depletion with long-term use, which is well documented and under-monitored
- Reduced appetite
Stop and get medical help
- Significantly reduced kidney function, since metformin is renally cleared and accumulation is what causes lactic acidosis
- Rapid breathing, muscle pain, unusual fatigue and abdominal pain together, which is how lactic acidosis presents. It is rare and it is a medical emergency
- Any procedure involving iodinated contrast, which normally requires temporarily stopping the drug
- Acute illness with dehydration, vomiting or reduced intake
Sources
From the community
Discussion for this compound concentrates in r/longevity, r/diabetes_t2 and r/Biohackers.
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