Dr mercola sights every study he is referencing in his writings I read them all, the studies that is and decide for myself. There has been a lot of censoring going on so i'm not sure all the links will work when you try. My favorite place to research is pub med. A lot of studies on natural compounds and their effects often studied so that a component from the natural substance can be removed and patented. I also am signed up to the New England Journal of Medicine.. it's free and JAMA just for reference on studies. I will keep adding to this Blog if new information comes to my attention that is helpful.
This is doctor Brownstein from Michigan
https://www.cebm.net/covid-19/n-acetylcysteine-a-rapid-review-of-the-evidence-for-effectiveness-in-treating-covid-19/
https://articles.mercola.com/sites/articles/archive/2020/05/25/nac-and-glutathione.aspx?cid_source=dnl&cid_medium=email&cid_content=art1HL&cid=20200525Z1&et_cid=DM547435&et_rid=879503162