So, on the FDA page it says they are considering allowing it as a supplement since it was marketed as a drug first, but as of right now it is only a drug. All the listings that have that as an ingredient are technically illegal, according to the FDA's page on NAC products, because this has not been approved yet. I would definitely steer clear of investing time and money into selling this on Amazon.

2022: "FDA has determined that NAC is excluded from the dietary supplement definition under section 201(ff)(3)(B)(i) of the FD&C Act because NAC was approved as a new drug before it was marketed as a dietary supplement or as a food."

November 29, 2023: "Today, the FDA has added its systematic review of literature regarding N-acetyl-L-cysteine (NAC) to the Peer Review Agenda. The agency has completed its review of safety information related to NAC, which will now go through the peer review process as a next step. The FDA undertook this review as part of its evaluation of a citizen petition’s request for the agency to undertake rulemaking to provide that NAC is not excluded from the definition of “dietary supplement.”"