NAC (N-acetyl-cysteine) is a precursor to glutathione, which is used up by your liver to break down the primary toxic metabolite of alcohol: acetylaldehyde. NAC is known as an OTC hangover "preventative," but don't take it chronically because it is a mucolytic and messes with other processes.

Aside: as a non-alcoholic fermentation, kombucha contains a lot of acetylaldehyde, so avoid it during a hangover.