Actually, it was originally classified as a drug. Periodically FAD goes through the lists of (unregulated) substitutes to see if they are properly classified. In high doses, NAC is used as a liver detoxifier and has significant side effects. In low doses, as used for supplements, it seems quite safe.
Now the discussion has arisen about potentially reclassifying and regulating.

As we like to say here, stayed tuned for further developments. As of yesterday, it was still available in a number of places.

Sue