ATC code A16 Other alimentary tract and metabolism products is a therapeutic subgroup of the Anatomical Therapeutic Chemical Classification System, a system of alphanumeric codes developed by the WHO for the classification of drugs and other medical products. Subgroup A16 is part of the anatomical group A Alimentary tract and metabolism. Codes for veterinary use (ATCvet codes) can be created by placing the letter Q in front of the human ATC code: for example, QA16. ATCvet codes without corresponding human ATC codes are cited with the leading Q in the following list.