NAC is a precursor of glutathione, an important antioxidant, which, if available throughout the body in sufficient quantities, can very effectively neutralize oxygen radicals even in the inner ear stressed by acoustic trauma, insufficient oxygenation or ototoxic drugs.
Before visiting the noisy places (pubs, concerts, shooting) it is recommended in addition to classical hearing protection (earmuffs, earplugs) to take 1200 mg of antioxidant at least an hour or two before the event. It is also good to take it regularly. Personally, I take 3 times a day 600 mg NAC and before visiting the dentist I use 1,200 mg. It is believed that large amount of NAC could protect ear cells against acoustic trauma completly. This means that, despite the long-term stay in noisy rock concert, inner ear should not suffer significant damage. Personally, I have not tried it, but it is clear that NAC increases the chances of survival of auditory cells under metabolic stress.
http://hearinghealthmatters.org/hearthemusic/2012/l-nac-and-hearing-loss-prevention-from-loud-music/
NAC also tested in the US military and its effectiveness was confirmed:
http://www.ncbi.nlm.nih.gov/pubmed/22122955
