This is the CodeSystem that contains codes in both WHO ATC (http://www.whocc.no/atc) and WHO ATC (http://www.whocc.no/atc).
This code system http://hl7.org/fhir/comparison/CodeSystem/a51fcf0b-5801-4baf-ad55-a337a1600c4b-3297 defines codes, but no codes are represented here