Back in 2001, it was speculated that ” the dietary supplements glutathione, N-acetylcysteine, alpha-lipoic acid, oligomeric proanthocyanidins, Ginkgo biloba, and Vaccinium myrtillus (bilberry) may be beneficial [for CFS].”  This suggestion is repeated 6 years later – “It is suggested that CFS patients should be treated with antioxidants, which inhibit the production of NFkappabeta, such as curcumin, N-Acetyl-Cysteine, quercitin, silimarin, lipoic acid and omega-3 fatty acids.” .
Positive results were obtained from combined use of ” glutamine, N-acetyl cysteine and zinc… A good clinical response is significantly predicted by attenuated IgA and IgM responses to LPS, the younger age of the patients, and a shorter duration of illness (< 5 years).” in . Similar mixtures of “L-carnitine, coenzyme Q10, taurine + lipoic acid, with or without curcumine + quercitine or N-acetyl-cysteine, zinc + glutamine” study ended up with the need to do proper controlled studies.. 
Well, some 16 years after it was suggested, we do not find actual studies! So, let us see what we find using our model…
- Antibacterial effects of N-acetylcysteine against endodontic pathogens.
- “we conclude that NAC has excellent antibacterial and antibiofilm efficacy against endodontic pathogens”
- “An increase (P < 0.05) in gut Lactobacillus and Bifidobacterium, accompanied with a decrease (P < 0.05) in Escherichia coli counts, was also observed in the NAC group.” 
- ” NAC appears to be a promising, non-antibiotic alternative to prevent biofilm-associated infections.” 
- “N-acetylcysteine (NAC) enhances the release of histamine” 
When you take NAC, one half of it will be out of your body in 6 hours [5.6 hrs half life]. If you take it once per day, the amount left before you take it again is just 1/16 (8%) of when you took it. I would suggest taking NAC every 8 hours to get the maximum benefit.
It definitely have benefits when taken with anti-infection herbs and some probiotics. If you have histamine issues, you may wish to take care.