# Metformin as an anti-ageing drug after cancer

Source: https://onco.cc/technologies/rejuv-frontier-metformin-ageing/  
OnCo record `rejuv-frontier-metformin-ageing` (Technology). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Metformin is cheap, old and safe enough that it is the obvious candidate for a drug that slows ageing. The largest cancer trial ever run on it, in 3,649 women with breast cancer, found nothing. The trial designed to test whether it slows ageing itself has not been run.

## Summary

The case for metformin rests on observational data in people with diabetes, on laboratory work on AMPK, mTOR and mitochondrial complex I, and on a small mechanistic trial. In MILES, 14 participants of about 70 took metformin and placebo for six weeks each in a randomised double-blind crossover; 647 genes were differentially expressed in muscle and 146 in fat, with changes in DNA repair, mitochondrial fatty acid oxidation and collagen pathways. That is a transcriptional signature, not a health outcome.

The outcome trial in cancer is MA.32: 3,649 people with high-risk non-metastatic breast cancer and without diabetes, randomised to metformin 850 mg twice daily or placebo for five years, with follow-up to October 2020. In the hormone receptor-positive group, invasive disease-free survival events occurred at 2.78 per 100 patient-years on metformin against 2.74 on placebo (hazard ratio 1.01, 95% CI 0.84 to 1.21, P = 0.93); deaths at 1.46 against 1.32 per 100 patient-years (hazard ratio 1.10, P = 0.47). In the receptor-negative group futility was declared at interim. Grade 3 non-haematological toxic events were more frequent on metformin (21.5 against 17.5 per cent, P = 0.003). This is an adequately sized randomised trial and it found nothing for the cancer outcome it tested.

TAME, the trial designed to test metformin as a geroprotector against a composite of age-related disease, has been proposed for a decade and has not started. So the honest position is: metformin is a good drug for diabetes, it did not improve breast cancer outcomes when properly tested, and whether it slows human ageing is unknown. It is not a reason to take it after cancer treatment, and it is not harmless: it lowers vitamin B12 and causes gastrointestinal effects in a substantial minority.

## Fields

- Kind: Technology
- Status: phase-3
- Last checked: 2026-10-02
- Tags: rejuvenation; survivorship; evidence:insufficient; repurposing
- Principle: Metformin inhibits mitochondrial complex I, raising the AMP to ATP ratio and activating AMPK, which suppresses mTORC1 and gluconeogenesis. The geroprotection hypothesis is that this mimics part of the caloric-restriction response; the oncology hypothesis was that lowering insulin would slow insulin-driven tumour growth.
- Strengths: Decades of safety data at the doses used; Inexpensive and generic; A mechanistic randomised crossover trial shows it changes ageing-relevant pathways in human muscle and fat
- Limitations: MA.32, the definitive cancer trial, was negative on its primary endpoint; More grade 3 non-haematological toxicity than placebo in that trial; The trial designed to test it as a geroprotector has not been run; Lowers vitamin B12 with long-term use

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Metformin
- Goodwin et al., Effect of metformin vs placebo on invasive disease-free survival in patients with breast cancer: the MA.32 randomized clinical trial (JAMA 2022): https://doi.org/10.1001/jama.2022.6147
- Kulkarni et al., Metformin regulates metabolic and nonmetabolic pathways in skeletal muscle and subcutaneous adipose tissues of older adults (Aging Cell 2018): https://doi.org/10.1111/acel.12723

## Connected records

- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/)
- fronts: [Recovery & Rejuvenation](https://onco.cc/fronts/rejuvenation/), [Supportive Care & Survivorship](https://onco.cc/fronts/supportive-care/)
- technologies: [Survivorship care and late-effects surveillance](https://onco.cc/technologies/survivorship-care-plan/), [What actually works after treatment](https://onco.cc/technologies/rejuv-frontier-what-works/)
- terms: [Late effects and survivorship toxicity](https://onco.cc/terms/late-effects/)
- bottlenecks: [Survivorship and late effects are neglected](https://onco.cc/bottlenecks/b-survivorship/)

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