N-acetylcysteine (NAC)

About N-acetylcysteine (NAC)

An acetylated form of the amino acid cysteine, used as a mucolytic and as the antidote for paracetamol overdose. It supplies the cysteine that limits glutathione synthesis.

NAC is a proper drug that also sits on supplement shelves, and its evidence is strongest where it is used as a drug: intravenous or oral NAC in paracetamol poisoning is life-saving and is standard emergency care. Beyond that, a large trial in chronic obstructive pulmonary disease found 600 mg twice daily reduced exacerbations, and psychiatric trials — trichotillomania, obsessive-compulsive disorder, addiction — have produced a scattering of positive and negative results that have not settled. Its regulatory position in the US is genuinely odd: the FDA has stated that NAC is excluded from the definition of a dietary supplement because it was approved as a drug first, then announced it would exercise enforcement discretion.

Sold as

Capsule, Effervescent tablet, Nebuliser solution, Intravenous (hospital)

Standardised to

mg N-acetylcysteine — a product without this marker may not resemble what was studied.

Also known as

NAC, Acetylcysteine, N-acetyl-L-cysteine

Regulation: Approved as a drug for paracetamol overdose and as a mucolytic. In 2020 the FDA took the position that NAC is excluded from the dietary supplement definition because it was approved as a drug before being marketed as a supplement; in 2022 the agency announced it intends to exercise enforcement discretion, leaving it widely sold but in an unusual legal position.

What the research used

The amounts, forms and durations published trials of N-acetylcysteine (NAC) actually administered.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.