I threw away all the NAC I had (prep for H5N1, etc.) because of something I read but can't remember what now. Will try to recollect.
This is from life extension magazine, so you might believe that there is some bias, however this article get to the nuts and bolts as to what NAC is capable of. It is, also very safe.
http://www.lef.org/magazine/2010/5/N-Acetyl-Cysteine/Page-01