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WHO Collaborating Centre for Drug Statistics Methodology

The Anatomical Therapeutic Chemical (ATC) classification system and the Defined Daily Dose (DDD) as a measuring unit have become the gold standard for international drug utilisation research. The system is developed and maintained by the WHO Collaborating Centre for Drug Research Methodology.

WHO logo.
WHO logo.

The Centre was established in 1982 as a central body responsible for coordinating the use of the ATC/DDD methodology. The Centre is located at the Norwegian Institute of Public Health in the Department of Pharmacoepidemiology, and is linked to the WHO headquarters in Geneva. It is funded by the Norwegian government.

Main activities:

  • to maintain and develop the ATC/DDD system
  • to classify drugs according to the ATC system 
  • to establish DDDs for drugs which have been assigned an ATC code 
  • to review and revise the ATC classification system and DDDs as needed 
  • to stimulate and influence the practical use of the ATC system by co-operating with researchers in the drug utilisation field 
  • to organise training courses in the ATC/DDD methodology and to lecture at these courses and seminars organised by others 
  • to provide technical support to countries in setting up their national medicines classification systems and build capacity in the use of medicine consumption information.

ATC/DDD system - International language for drug utilisation research

The ATC/DDD system is a tool for exchanging and comparing data on drug use at international, national or local levels. Access to standardised and validated information on drug use is essential to monitor drug utilisation patterns, identify problems in drug use, initiate educational or other interventions, and to monitor outcomes of these interventions.

WHO International Working Group for Drug Statistics Methodology

The Centre receives expert advice from the WHO International Working Group for Drug Statistics Methodology. This group represents the six WHO global regions and consists of twelve WHO appointed experts in clinical pharmacology, clinical medicine, international public health, drug utilisation and drug regulation.

The Working Group is responsible for the scientific development of the ATC/DDD system and is consulted when major questions arise. All new ATC codes, DDDs and decisions concerning ATC and DDD changes are discussed and approved by the Working Group.

New ATC/DDDs and alterations are published on the website after each meeting in the International Working Group. The Working Group meets twice annually.

ATC DDD logo.
ATC DDD.

More information

You will find information about the ATC/DDD system and publications on the Centre’s website, including:

  • ATC index with DDDs
    The complete index is published annually and is available in several formats. 
  • Guidelines for ATC classification and DDD assignment 
    The complete Guidelines are available as a pdf on the web site.

A searchable version of the index with text from the Guidelines linked to the ATC levels is accessible from the website. The search options enable the user to find ATC codes and DDDs based on substance name or ATC levels.