Essential medicines and health products

Drug Utilization: ATC/DDD

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 utilization research.
The ATC/DDD system is a tool for exchanging and comparing data on drug use at international, national or local levels.

The purpose of the ATC/DDD system is to serve as a tool for drug utilization research in order to improve quality of drug use. One component of this is the presentation and comparison of drug consumption statistics at international and other levels.

A major aim of the Centre and Working Group is to maintain stable ATC codes and DDDs over time to allow trends in drug consumption to be studied without the complication of frequent changes to the system. There is a strong reluctance to make changes to classifications or DDDs where such changes are requested for reasons not directly related to drug consumption studies. For this reason the ATC/DDD system by itself is not suitable for guiding decisions about reimbursement, pricing and therapeutic substitution.


2019 Meetings

Open session preceding the 46th meeting of the WHO International Working Group for Drug Statistics Methodology

  • Date: 17 October 2019
  • Time: 9:00-10:30
  • Location: Oslo, Norwegian Institute of Public Health

This is held once a year, in the interest of transparency, as a pre-meeting event before the actual meeting of the full Working Group for Drug Statistics Methodology. It is open to anyone with a legitimate interest in the system Anatomical Therapeutic Chemical (ATC) classification and Defined Daily Dose (DDD) assignment. It provides an opportunity for persons to present additional information to the experts to assist them in their decision making and also provides an opportunity for the experts to exchange ideas and opinions with interested parties.

There is no agenda for this session. However, should you wish to make a suggestion or intervention at this session you are invited to bring these to the attention of WHO when you register for the session.

In order to register for the Open Session preceding the 46th meeting of the Working Group on Drug Statistics Methodology, please send your name and affiliation before 5 October 2019 to

46th WHO International Working Group for Drug Statistics Methodology Meeting

17-18 October 2019, location: Oslo
Closed Session

Related publications