Metformin
Metformin is a common, cheap starting drug for type 2 diabetes, and it is widely promoted as an anti-aging pill. The claim that people taking it outlive people without diabetes rests on one heavily criticised records study, and a Danish national study that tested it again found the opposite; the trial meant to test it in healthy people has never started, and two trials found it blunts the gains from exercise.
If you are healthy, don't take metformin for longevity. If you have prediabetes, lifestyle change comes first; if you have type 2 diabetes, it remains a reasonable drug to discuss with your doctor.
What it is
Metformin is a biguanide, a blood-sugar-lowering drug for type 2 diabetes (T2D). It switches on AMPK (AMP-activated protein kinase), the cell's energy-shortage signal and a counterweight to mTOR (the mechanistic target of rapamycin), the nutrient-sensing signal that rapamycin blocks. That mechanism is why it is proposed as a geroprotector, a drug that would slow aging itself. It has no approved use in healthy people without diabetes. The wider category is compared on Geroprotectors.
The survival claim, and why it doesn't hold up
Metformin's longevity reputation rests on long-term follow-up and records data. Long-term follow-up of the UKPDS randomised trial (the UK Prospective Diabetes Study), and the UK CPRD records database (Clinical Practice Research Datalink), showed lower death rates from any cause in people with T2D on metformin than on sulfonylureas, an older class of diabetes drug. That is a low bar: sulfonylureas are themselves associated with harm, so "better than a sulfonylurea" says little about aging.
The much-repeated claim that metformin users outlive people without diabetes comes from one 2014 UK records analysis.[1] It has been heavily criticised for built-in biases in how the groups were compared (known as immortal-time and comparator bias).
When a 2022 Danish national-register study tested the claim again, it found the opposite. Including twin pairs in which only one twin had diabetes, people starting metformin had higher death rates than matched people without diabetes.[2] Treat the survival claim as an association with a plausible confound, not evidence that metformin slows aging.
The animal record does not rescue it. Pooling lifespan studies across eight vertebrate species, a 2025 meta-analysis found that rapamycin, but not metformin, significantly extended lifespan.[3]
TAME: the trial that never started
TAME (Targeting Aging with Metformin) was designed to test aging outcomes in adults without diabetes, but it has never enrolled anyone. It has some money — about $5 million set aside by the US National Institute on Aging, plus private pledges — against an estimated cost of $45–70 million. A decade on it remains a proposal, not a study in progress, and no result is coming soon.[4]
It can blunt the gains from exercise
For an active adult this is the most concrete reason to avoid it.
- Aerobic training. In a 12-week trial in older adults, metformin weakened the gains in fitness (maximal oxygen uptake, VO₂max), insulin sensitivity and muscle mitochondrial function from aerobic training.[5]
- Strength training. In the MASTERS trial, healthy over-65s doing 14 weeks of strength training gained less muscle on metformin than on placebo, although their strength gains did not differ significantly.[6]
- Arteries. A small 2026 trial in adults at risk of metabolic syndrome found metformin altered some artery pressure-wave responses to training, with mixed blood-pressure results.[7]
Where it does belong
Prediabetes. Lifestyle change comes first: a structured programme aiming for 5–7% weight loss and at least 150 minutes a week of moderate activity. Doctors consider adding metformin for people at the highest risk — especially adults aged 25–59 with a body mass index (BMI) of 35 or more and higher fasting glucose and HbA1c (a marker of longer-term blood sugar), and women who have had gestational diabetes.[8]
Type 2 diabetes. It remains a common, cheap starting drug. But people with heart disease or high cardiovascular risk, or with kidney disease, are now steered to a sodium-glucose cotransporter-2 (SGLT2) inhibitor or a glucagon-like peptide-1 (GLP-1) drug whatever their HbA1c, and people with heart failure to an SGLT2 inhibitor, with or without metformin.[9]
Side effects
- Vitamin B12 deficiency with long-term use — have it checked periodically, especially after four to five years, at 1,500 mg a day or more, or with anaemia or numbness and tingling.[10]
- Stomach upset (gastrointestinal side effects), usually modest.
- Not for people with significant kidney impairment.
- With berberine: combining the two risks low blood sugar (hypoglycaemia).
- Blunted training gains, as above.
What to do
- Healthy and active: skip it. The survival evidence is confounded and the exercise penalty is measured in trials.
- Prediabetes: start with weight loss and activity; discuss metformin only if you are in a highest-risk group.
- Taking it for diabetes: keep training, and have your B12 checked periodically.
Further reading
- Keys MT et al. Reassessing the evidence of a survival advantage in Type 2 diabetes treated with metformin compared with controls without diabetes: a retrospective cohort study. Int J Epidemiol 2022.[11]
- Bannister CA et al. Can people with type 2 diabetes live longer than those without? A comparison of mortality in people initiated with metformin or sulphonylurea monotherapy and matched, non-diabetic controls. Diabetes Obes Metab 2014.[12]
- Konopka AR et al. Metformin inhibits mitochondrial adaptations to aerobic exercise training in older adults. Aging Cell 2019.[13]
- Ivimey-Cook ER et al. Rapamycin, Not Metformin, Mirrors Dietary Restriction-Driven Lifespan Extension in Vertebrates: A Meta-Analysis. Aging Cell 2025.[14]
- Walton RG et al. Metformin blunts muscle hypertrophy in response to progressive resistance exercise training in older adults: A randomized, double-blind, placebo-controlled, multicenter trial: The MASTERS trial. Aging Cell 2019.[15]