ATC Classification

The Anatomical Therapeutic Chemical (ATC) classification is an international drug classification system maintained by the WHO Collaborating Centre for Drug Statistics Methodology. It organizes active substances into a hierarchical structure based on the organ or system they act on (anatomical group), their therapeutic purpose, and their chemical properties. ATC is used worldwide for drug utilization research, formulary management, epidemiological studies, and national health statistics.

ATC codes are structured by length: a one-letter anatomical main group (e.g., C for cardiovascular system), expanding to five levels with codes up to seven characters at the chemical substance level (e.g., C10AA05 for atorvastatin). Each level adds therapeutic or chemical specificity. The related Defined Daily Dose (DDD) measure provides a standard unit for comparing drug utilization across products and countries.

Unlike product-level terminologies such as SNOMED CT or RxNorm, ATC classifies substances by therapeutic and chemical class — not by brand, strength, or package. A single ATC code may correspond to many commercial products. This makes ATC ideal for population-level analytics, formulary grouping, and reporting, while product identity systems handle prescribing and dispensing workflows.

Medication catalogs and mapping platforms such as OpenMed link hospital and registry entries to ATC codes alongside SNOMED CT and other identifiers. ATC complements product-level mappings: SNOMED CT answers which exact drug product is involved, while ATC answers which therapeutic class it belongs to for analytics and formulary organization.