There are many situations where a classification system (not just an identification system) for medicines is needed. The problem is the lack of an international standard. The Anatomical, Therapeutic Chemical drug classification system is developed and maintained by the WHO collaborating Centre of Drug Statistics Methodology, Norway. It is a hierarchical, 5-level system, where the fifth level is the chemical substance. More about the ATC (Anatomical Therapeutic Chemical) system can be found at the home page of the WHO Collaborating Centre for Drug Statistics Methodology.