Here is what our amazon rep says about why straight NAC products are still on amazon, while multi-ingredient supplements containing NAC are being removed:

Essentially, to sell NAC on Amazon, NAC must be the only active ingredient. It cannot be included in a multi-vitamin or any supplement with other active ingredients. This violates Amazon’s Drugs & Drug Paraphernalia policy. Please see the below blurb which contains the exact FDA guidelines around NAC. The Restricted Products team is identifying and removing all ASINs which contain NAC plus additional active ingredients. Unfortunately, there are no appeal paths for this decision. Please take a look at the linked policy and the below statement and let me know if you have any questions.

Based on the product label, it appears that you intend to market your product, which contains N-acetyl-L-cysteine (NAC), as a dietary supplement. Your product cannot be a dietary supplement, because it does not meet the definition of dietary supplement under section 201(ff) of the Act [21 U.S.C. § 321(ff)]. FDA has concluded that NAC products are excluded from the dietary supplement definition under section 201(ff)(3)(B)(i) of the Act [21 U.S.C. § 321(ff)(3)(B)(i)]. Under this provision, if an article (such as NAC) has been approved as a new drug under section 505 of the Act [21 U.S.C. § 355], then products containing that article are outside the definition of a dietary supplement, unless before such approval that article was marketed as a dietary supplement or as a food. NAC was approved as a new drug under section 505 of the Act [21 U.S.C. § 355] on September 14, 1963. FDA is not aware of any evidence that NAC was marketed as a dietary supplement or as a food prior to that date.