N-acetylcysteine (NAC)

N-acetylcysteine (NAC) is a tweaked form of the amino acid cysteine. In the clinic, it loosens mucus and serves as the standard antidote for acetaminophen (paracetamol) overdose. Its main trick, in both medicine and longevity, is refilling your cells' cysteine. Cysteine is the rate-limiting ingredient for making glutathione, your body's master antioxidant. By restoring glutathione, it helps your cells mop up reactive oxygen species, keep mitochondrial redox in balance, and run phase II detox. Its oral absorption is moderate and variable, since the liver processes a lot on first pass. So liposomal and slow-release versions are being studied. Beyond antioxidants, NAC also calms NF-κB inflammatory signaling. And it may soften cysteine-related DNA methylation shifts. On its own, it has been tested in COPD, psychiatric conditions, and metabolic disease, with mixed results. In the longevity world, it matters most as the cysteine-donating half of the GlyNAC combo.

Last reviewed: June 22, 2026

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