Loren Pickart, the peptides discoverer, estimated toxic action beginning around 22,500mg, a dose that would be essentially impossible to reach accidentally
A meta-analysis of studies using NAC to increase athletic performance found that there were more side effects (none severe) at 20g/day.[ref] High doses of NAC are used in hospitals by IV for reversing acetaminophen toxicity
[DOI] [PubMed] [Google Scholar] 21.Niu LY, Guan YS, Chen YZ, Wu LZ, Tung CH, Yang QZ
J Thorac Oncol 2020;15:e129e131
However, there seems to be a balance required for sulfur, so it may be that a person could have an underlying reason to react negatively toward sulfur-containing foods, making it a secondary problem as opposed to a primary issue