This is a summer 2020 submission and fall 2020 publication (doesn’t make it wrong, just gives timing context).

I was recommended NAC supplements and some cursory research suggested that it probably wasn’t going to hurt so I bought them ($14 a bottle) as a readily available OTC supplement. FDA sent out some threatening communications in fall 2020 which suggested they’d contemplate prosecuting the sales of NAC as a supplement and it predictably got a lot harder to find. I’m still taking some of the first 500 pills I bought as it seems unlikely to be harmful. (I’m not claiming it works, just giving some background not in the NIH paper.)