Metformin
/ Biguanide-class oral antihyperglycaemic (small molecule); complex I inhibition; AMPK activatorALIAS · Metformin hydrochloride · Glucophage (trade) · Glucophage XR · Riomet
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Tier 1. FDA-approved 1995 for type 2 diabetes; multi-decade global first-line oral antihyperglycaemic with extensive Phase 3 and post-marketing data. Geroscience interest in metformin as an aging intervention is driven by the planned TAME trial (Targeting Aging with Metformin, Barzilai and colleagues) — a trial design rather than completed evidence, in development as of 2026.
Metformin is a small biguanide molecule that accumulates in mitochondria of metabolically active tissues (hepatocytes, intestinal epithelium) and produces its principal antihyperglycaemic effect through inhibition of mitochondrial complex I, with downstream consequences including decreased ATP and increased AMP, AMPK activation, and suppression of hepatic gluconeogenesis. Additional proposed mechanisms include modulation of mitochondrial glycerophosphate dehydrogenase, alterations in gut microbiome composition, and effects on bile acid metabolism — none of which has fully displaced complex I inhibition as the leading explanation for the glucose-lowering effect.
The geroscience hypothesis — that the same AMPK activation and reduced mTOR signalling that contribute to glucose lowering may also engage canonical aging pathways including autophagy induction, mitochondrial biogenesis, and reduced senescent cell burden — provides a mechanistic rationale for the TAME trial framing, but mechanistic plausibility is distinct from controlled-trial demonstration of geroscience benefit.
Tier 1 for the type 2 diabetes indication. The UKPDS 34 trial (UK Prospective Diabetes Study Group, Lancet 1998) randomised 1,704 overweight participants with newly diagnosed T2D to metformin or conventional diet therapy and demonstrated reduced diabetes-related death and all-cause mortality over a median ten-year follow-up. Bannister and colleagues (2014) compared metformin-treated diabetics to sulfonylurea-treated diabetics and to non-diabetic controls in a UK primary care cohort, observing survival comparable to or modestly exceeding non-diabetic controls — a widely-cited (and methodologically debated) source of geroscience interest. The TAME trial design (Barzilai and colleagues, 2016) describes a proposed multi-centre Phase 3 trial of metformin to delay age-related morbidity in older non-diabetic adults; as of 2026 the trial framework has informed regulatory dialogue about geroscience trial design but completed efficacy data on healthy-aging endpoints are not yet available.
The principal acute concern is lactic acidosis, historically associated with phenformin and the reason for the conservative renal-function labelling on metformin; clinical experience and large database studies indicate the absolute risk in appropriately selected populations is low. Common gastrointestinal adverse events (nausea, diarrhoea, abdominal discomfort) are dose-related and frequently dose-limiting at initiation. Long-term metformin use is associated with vitamin B12 deficiency in a fraction of recipients, prompting periodic monitoring guidance.
Regulatory status
- FDA status:
- FDA-approved
- Compounding:
- Not eligible for compounding (approved, not in shortage)
Geroscience use of metformin in healthy non-diabetic older adults remains pre-evidence; the existing approved-use data establish an excellent safety and efficacy profile for diabetes but do not extrapolate automatically to aging-as-indication. The MASTERS trial (metformin and resistance training in older adults, Walton and colleagues 2019) reported metformin attenuated some hypertrophic responses to exercise — a finding that complicates the simple 'metformin extends healthspan' narrative. The TAME trial, if and when completed, would be the definitive test of the geroscience hypothesis.