ATCsystemet

ATCsystemet (the ATC classification system) is an internationally used method for classifying active substances in medicines according to the organ or system on which they act and their therapeutic, pharmacological and chemical properties. Developed under the auspices of the World Health Organization in the 1970s, the system is maintained and updated by the WHO Collaborating Centre for Drug Statistics Methodology.

The ATC structure is hierarchical and comprises five levels. The first level is an anatomical main group designated by a single letter; subsequent levels progressively specify therapeutic main group, pharmacological subgroup, chemical subgroup and the chemical substance, resulting in a unique alphanumeric code for each active ingredient. The system is commonly used together with the Defined Daily Dose (DDD), a statistical measure of average maintenance dose for the main indication in adults, to enable standardized comparisons of drug consumption.

Applications of ATCsystemet include drug utilization research, pharmacoepidemiology, health policy planning, reimbursement systems and international comparisons of medicine use. National authorities, pharmacies and researchers frequently employ ATC codes in databases, prescription registries and statistical reports. Many countries, including Sweden, refer to the system as ATCsystemet in official documents and datasets.

Limitations include periodic revisions that may lag behind market changes, incomplete coverage of combination products or new therapeutic classes, and the fact that DDDs do not necessarily reflect recommended or prescribed doses for individual patients. Despite these constraints, the ATC classification remains a central tool for organizing and analyzing medicinal product information.