💊 Medication
metformin
First-line type-2-diabetes drug, also used off-label for longevity. Strong evidence it prevents/delays diabetes, lowers insulin resistance, and causes modest weight loss — but it also depletes vitamin B12 and blunts some exercise gains, and its cancer-prevention, cardiovascular, and lifespan-extension claims are contested.
4 well-supported · 0 disputed. This shows how settled each sub-question is, not whether metformin is "good." Direction lives in each claim below.
The 7 claims about metformin
Each keeps its own verdict — we never average them away.
Does metformin dampen the benefits of exercise?
Strong support Yes, blunting fitness and muscle gains in older adults — a real trade-off worth weighing.
Does metformin cause vitamin B12 deficiency?
Strong support Yes — long-term metformin lowers serum B12 and raises risk of biochemical deficiency in a dose- and duration-dependent way, confirmed by both the DPPOS and a placebo-controlled RCT plus meta-analyses; clinically overt deficiency is less common but real.
Does metformin prevent or delay progression from prediabetes to type 2 diabetes?
Strong support Yes — RCTs consistently show metformin cuts diabetes incidence in prediabetes by ~25-30%, though less than intensive lifestyle, and much of the effect reflects pharmacologic glucose-lowering that partly unmasks on washout.
Does metformin cause modest weight loss?
Strong support Yes — metformin produces small, durable weight loss (~2-3 kg vs placebo), modest but real, in both diabetic and non-diabetic overweight populations.
Does metformin reduce cardiovascular risk in type 2 diabetes?
Contested Genuinely uncertain — the benefit rests largely on one small subgroup of an old trial (UKPDS-34); later RCTs and meta-analyses of randomized data are mixed-to-null, so cardioprotection is plausible but not robustly proven.
Does metformin reduce cancer risk?
Contested Contested — observational cohorts and their meta-analyses suggest lower cancer incidence, but those associations are heavily confounded by time-related (immortal-time) bias, and bias-corrected analyses, target-trial emulations, and the one cancer-endpoint RCT show little or no true effect.
Is metformin proven to extend healthy human lifespan?
Contested No — the definitive trial (TAME) has not reported outcomes and existing human evidence is indirect/confounded, so "fuzzy/inconclusive" is accurate; corroborates the vault's existing contested state.
Educational only, not medical advice. Hub descriptions are curated for honesty; see the methodology.