So big mistake here: NAC is not harmless. It does have side effects and it also has toxicity at high doses.
It has not been studied in long term use orally or IV, it's main use bomg short term use for paracetamol overdose treatment. Inhalation is more studied but it is not absorbed into the body in the same way.
We think it is safe but we haven't actually done human trials to be sure. What we have found in mice is that high doses can cause lung and heart damage and also when it comes to alcohol it is protective if taken before alcohol consumption BUT it amplifies the toxicity to the liver if about 4 hours taken after alcohol. All of this is summarised on the Wikipedia page which looks to be good quality.
Overall it may be a useful drug but don't take it off label or self medicating. Medicine is littered with unexpected effects of drugs that only came out once it was too late. Thalidomide is a good example - a "wonder drug" for nausea used in pregnancy that was not tested and caused horrific birth defects which only became evident when it was too late.
Your body is not a lab, be careful experimenting with supposedly "safe" drugs.
guyrocket