Max Rady College of Medicine

Concept: Anatomical Therapeutic Chemical (ATC) Classification System

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Concept Description

Last Updated: 2008-09-30


Classification Levels

    In the ATC classification system, drugs are divided into different groups according to the organ or system on which they act and their chemical, pharmacological and therapeutic properties. Drugs are classified into groups at 5 different levels:

    • 1st level - At the broadest level, drugs are divided into one of the following fourteen anatomical groups. The first level of the code is based on a letter e.g. "B" for Blood and blood forming organs:
      Level Main Group
      A Alimentary tract & metabolism
      B Blood & blood forming organs
      C Cardiovascular system
      D Dermatologicals
      G Genitourinary system & sex hormones
      H Systemic hormonal preparations
      J Antiinfectives for systemic use
      L Antineoplastic & immunomodulating agents
      M Musculo-sketal system
      N Nervous system
      P Antiparasitic products
      R Respiratory system
      S Sensory organs
      V Various

    • 2nd level - is either a pharmacological or therapeutic subgroup (e.g., "B03" for Anti-anemic preparations).

    • 3rd level - is a chemical or therapeutic or pharmacological subgroup (e.g., "B03A" for Iron Preparations).

    • 4th level - is a chemical or therapeutic or pharmacological subgroup. This is the level used to count "number of different drugs" as it is the level which aggregates drugs just above their descriptive chemical substance, (e.g., "B03AA" for Iron, bivalent, oral preparations). A count of an individual's drugs at the fourth level of ATC gives the researcher a categorical option with which to stratify and then describe pharmaceutical users. It approximates a measure of comorbidity.

    • 5th level - is the subgroup for the chemical substance (e.g., "B03AA07" Ferrous sulphate).

    In the ATC system all DINs (drug identification numbers) with the generic name "ferrous sulphate" would be assigned the code B03AA07. In other words, an ATC code has five levels that are described by seven digits.

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  • Metge C, Kozyrskyj A, Dahl M, Yogendran M, Roos NP. Pharmaceuticals: Focussing on Appropriate Utilization. Winnipeg, MB: Manitoba Centre for Health Policy, 2003. [Report] [Summary] (View)
  • Norwegian Institute of Public Health. Guidelines for ATC classification and DDD assignment: 7th edition. Oslo, Norway: WHO Collaborating Centre for Drug Statistics Methodology; 2003.(View)
  • Sketris IS, Metge CJ, Ross JL, MacCara ME. The use of the World Health Organization anatomical therapeutic chemical/defined daily dose methodology in Canada. Drug Information Journal 2004;38(1):15-27.(View)
  • World Health Organization (WHO). W.H.O.'s Collaborating centre for drug statistics methodology: Guidelines for ATC classification and DDD assignment. Oslo, Norway: 1996.(View)


  • pharmaceuticals
  • World Health Organization

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Manitoba Centre for Health Policy
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