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Metformin (Longevity Context) Side Effects & Safety

Evidence:Emerging
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This content is for informational purposes only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease. Individual results may vary — consult your healthcare provider before starting any supplement. Full disclaimer

Safety Profile

Overall safety rating: Safe with Caution

Potential Side Effects

  • GI symptoms — diarrhea, nausea, bloating, and abdominal cramping affect 20-30% of users; extended-release reduces these
  • Vitamin B12 depletion — long-term metformin use reduces B12 absorption by up to 30%; supplement B12 and monitor levels
  • Lactic acidosis — extremely rare but serious; risk increases with kidney impairment, alcohol use, and dehydration
  • Metallic taste in mouth
  • May blunt exercise adaptations — Konopka et al. (2019) found metformin attenuated mitochondrial and cardiorespiratory improvements from aerobic exercise in older adults

Drug & Supplement Interactions

  • Alcohol — increases lactic acidosis risk; moderate use only
  • Contrast dye (for CT scans) — metformin must be held before and after iodinated contrast to prevent lactic acidosis
  • Kidney-affecting medications — metformin is renally cleared; drugs that impair kidney function increase toxicity risk
  • Insulin and sulfonylureas — additive hypoglycemia risk
  • Exercise — may attenuate some exercise-induced mitochondrial adaptations; some practitioners cycle metformin around intense training

Maximum Dose

Do not exceed: 2000mg/day (for diabetes; longevity doses typically lower at 500-1000mg)

Full Metformin (Longevity Context) Guide

References

  1. ObservationalBannister CA, Holden SE, Jenkins-Jones S, et al. (2014). 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, Obesity and Metabolism. DOI PubMed
  2. Meta-analysisGandini S, Puntoni M, Heckman-Stoddard BM, et al. (2014). Metformin and cancer risk and mortality: a systematic review and meta-analysis taking into account biases and confounders. Cancer Prevention Research. DOI PubMed
  3. RCTKonopka AR, Laurin JL, Schoenberg HM, et al. (2019). Metformin inhibits mitochondrial adaptations to aerobic exercise training in older adults. Aging Cell. DOI PubMed