A decades-old, inexpensive diabetes drug and a leading longevity candidate. Strong evidence it improves blood sugar and prevents diabetes in those with metabolic problems; the aging-slowing claim stays unproven, resting on observational data. Common digestive upset, long-term vitamin B12 lowering, and rare acid buildup tied to poor kidney function. May dampen exercise gains. (Full Review)
| Marker | Target | Why |
|---|---|---|
| eGFR (kidney filtration) | >90 mL/min/1.73m² | Governs drug clearance and lactic-acidosis risk |
| HbA1c (3-month glucose) | <5.4% (functional) | Tracks glycemic response and metabolic benefit |
| Fasting glucose | 70–85 mg/dL (functional) | Direct measure of glucose-lowering effect |
| Fasting insulin | <5–6 µIU/mL (functional) | Assesses insulin resistance, a key benefit target |
| Vitamin B12 | >500 pg/mL (functional) | Detects metformin-induced depletion before nerve damage |
| Methylmalonic acid | Within lab reference range | Confirms functional B12 status when B12 borderline |
| Lipid panel | Optimized per cardiovascular goals | Metformin may modestly improve triglycerides/LDL |
| Liver enzymes (ALT/AST) | Within reference range | Screens for liver disease that raises lactic-acidosis risk |
Cadence: Kidney function and metabolic markers at baseline and 3–6 months, then annually (every 6 months if eGFR is reduced or age >65); vitamin B12 at baseline and every 1–2 years.