GlyNAC (Glycine + N-acetylcysteine)

GlyNAC is the combined oral supplementation of glycine and N-acetylcysteine (NAC), designed to replenish both precursors of the tripeptide glutathione (γ-Glu-Cys-Gly), which declines progressively with age. The combination addresses the limiting precursors simultaneously — cysteine (via NAC) and glycine — rather than the gamma-glutamylcysteine step, which is typically less rate-limiting in older adults. Pioneered by Rajagopal Sekhar and colleagues at Baylor College of Medicine, a series of randomized, double-blind pilot trials in older adults (GlyNAC trials, published 2021–2024) using 16–24 weeks of supplementation documented restoration of erythrocyte glutathione to levels seen in young adults and improved multiple aging-associated deficits including mitochondrial fuel oxidation, oxidative stress, inflammation, endothelial dysfunction, insulin resistance, genomic damage, muscle strength, and gait speed. Evidence remains limited to short-duration trials with small samples; longer-term RCTs with clinical outcome endpoints are lacking. GlyNAC is commercially available as a dietary supplement and has no approved indication.