NAC — Forms, Dosage & Interactions

N-Acetyl Cysteine (NAC) is a semi-essential amino acid derivative and the direct precursor to glutathione — the body's primary endogenous antioxidant. It is synthesised from L-cysteine, an amino acid found in high-protein foods such as meat, eggs, and dairy, though dietary intake alone rarely raises glutathione levels meaningfully. NAC has one of the longest clinical track records of any supplement compound, having been used in NHS hospitals for decades as an intravenous antidote for paracetamol overdose, where it rapidly restores hepatic glutathione to prevent liver failure. Beyond its well-established pharmaceutical applications, a substantial body of research has investigated NAC's potential for supporting respiratory health, liver function, cognitive wellbeing, and oxidative stress management. Studies indicate it may reduce circulating oxidative stress markers, modulate inflammatory signalling cascades, and influence glutamate neurotransmission in the central nervous system. The overall evidence base is rated strong relative to most supplement ingredients — notable given that many dietary supplements have limited clinical trial data. Individual responses may vary depending on baseline glutathione status, dietary cysteine intake, and health context. In the UK, NAC is available over the counter as a food supplement, entirely distinct from its licensed pharmaceutical use.