Methylene blue

Methylene blue (MB) is a synthetic phenothiazine dye with FDA approval (Provayblue, 2016) for treatment of acquired methemoglobinemia at an initial dose of 1 mg/kg intravenously, with a repeat dose of 1 mg/kg if needed (total up to 2 mg/kg). At low concentrations (nanomolar to low micromolar), it acts as a redox cycler in the mitochondrial electron transport chain, accepting electrons from NADH and donating them to cytochrome c, thereby bypassing dysfunctional complexes I and III and supporting ATP synthesis. In cell culture and rodent models, low-dose MB has reduced mitochondrial reactive oxygen species, improved memory in aged animals, and attenuated neurodegeneration-related pathology. Interest in MB for aging stems partly from a small number of human trials investigating cognitive effects in healthy older adults or early Alzheimer's disease, with mixed and modest results; no aging or longevity indication has been approved, regulatory frameworks for low-dose oral use vary by country, and recommendations for off-label use as a longevity agent are unsupported by RCT evidence.