See superscript 6 on the article. Apparently NAC might has side effects of its own.
One of the side effects in a study in mice was inducing lung cancer: https://doi.org/10.1172/jci.insight.127647
alt Hacker News
One of the side effects in a study in mice was inducing lung cancer: https://doi.org/10.1172/jci.insight.127647