ATC Code Explorer

Explore the World Health Organization's Anatomical Therapeutic Chemical (ATC) classification system. Browse from anatomical main groups (Level 1) down to individual chemical substances (Level 5). Each level reveals the pharmacological and therapeutic context of a drug within the classification hierarchy.

Disclaimer: This tool is for educational purposes only. Always consult a healthcare professional for medication decisions.

Level 1 — Anatomical Main Group

Level 2 — Therapeutic Subgroup

Level 3 — Pharmacological Subgroup

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Example Drugs in This Group

The ATC Classification System

The Anatomical Therapeutic Chemical (ATC) classification system, maintained by the WHO Collaborating Centre for Drug Statistics Methodology, organizes drugs into a five-level hierarchy. Level 1 identifies the anatomical or pharmacological main group (14 groups, coded A through V). Level 2 designates the therapeutic subgroup. Level 3 identifies the pharmacological subgroup. Level 4 specifies the chemical subgroup, and Level 5 identifies the individual chemical substance. This standardized coding system enables international comparison of drug utilization data and supports pharmacoepidemiological research across healthcare systems.

Each ATC code consists of seven alphanumeric characters. For example, metformin is classified as A10BA02: A (Alimentary tract and metabolism), 10 (Drugs used in diabetes), B (Blood glucose-lowering drugs, excl. insulins), A (Biguanides), 02 (metformin). The system assigns each drug a single code based on its main therapeutic use, though a substance may have different codes if used in different formulations or for distinct indications. The ATC system is widely used in prescription monitoring, drug utilization reviews, and health economics research.

Understanding ATC codes helps identify drugs within the same pharmacological class that may serve as therapeutic alternatives, aids in detecting drug class-level safety signals in pharmacovigilance databases, and supports formulary management decisions. National drug registers in Scandinavia, prescription monitoring programs, and WHO essential medicines analyses all rely on ATC coding as the standard drug classification vocabulary.

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This content is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making medication decisions.

Data sources: ChEMBL, PubChem, DailyMed.

How to Use

1
Browse or search the ATC hierarchy
Navigate the WHO ATC five-level classification tree starting from anatomical main groups (A through V) or use the search function to find a drug by name and retrieve its assigned ATC code. The tool uses the WHO ATC/DDD Index as the authoritative reference, updated annually by the WHO Collaborating Centre in Oslo.
2
Explore drugs at each classification level
At any ATC level, view all drugs classified within that node along with their DDD (Defined Daily Dose), route of administration code, and links to individual drug profiles. DDD values enable standardized comparison of drug utilization across health systems and time periods.
3
Compare drug utilization metrics
Use ATC/DDD units to compare prescribing patterns across drug classes or countries using standardized metrics (DDDs per 1,000 inhabitants per day or DDDs per 100 bed-days). This supports identification of prescribing outliers and pharmacoepidemiological analysis aligned with WHO pharmacovigilance methodology.

About

The WHO Anatomical Therapeutic Chemical (ATC) classification system is the international standard for drug classification and drug utilization research, established by the WHO to enable consistent comparison of drug prescribing and consumption data across countries, health systems, and time periods. The system's hierarchical architecture captures drugs at five levels of specificity from broad anatomical organ system to unique chemical substance, providing researchers and regulators with a flexible taxonomy suitable for analyses ranging from national formulary comparisons to granular pharmacoepidemiological studies of individual drug safety.

The ATC/DDD Index serves as the authoritative reference for both the classification codes and the defined daily doses used in utilization measurement. As of the 2024 edition, the index covers over 6,000 ATC codes representing substances actively marketed in multiple countries. The DDD concept provides the critical denominator enabling comparison: expressing drug exposure in DDDs per defined population per time period removes the confounding effect of different dose regimens and formulations, producing a measure proportional to the number of patients treated per day at the assumed maintenance dose. Nordic countries and the WHO Regional Office for Europe have developed pharmacoepidemiological methods using ATC/DDD data for more than 40 years, generating comparative prescribing atlases identifying variation in drug therapy patterns that may reflect differences in guideline adherence, disease burden, or prescribing culture.

This ATC code explorer makes the full WHO ATC hierarchy accessible in an interactive format, supporting pharmaceutical education, drug utilization analysis, and comparative pharmacology. By enabling navigation from broad anatomical groups to individual chemical substances, the tool supports understanding of where a drug fits in the therapeutic landscape — whether it is the first agent in a class (e.g., omeprazole as the first proton pump inhibitor, A02BC01) or one of many agents in a large well-established class, and how its pharmacological characteristics compare to related drugs at the fourth ATC level.

FAQ

How does the WHO ATC classification differ from FDA drug classification?

The WHO ATC system classifies drugs by anatomical target and therapeutic/pharmacological purpose in a five-level hierarchical code, enabling international standardized comparison of drug utilization. FDA classification uses Established Pharmacologic Class (EPC) terminology in approved drug labeling, reflecting mechanism of action or pharmacological class as reviewed during the approval process. ATC codes are assigned by the WHO Collaborating Centre rather than the originator company and may differ from commercial classification by indications; some drugs receive multiple ATC codes if they are used in substantially different therapeutic contexts. Both systems complement each other in pharmacoepidemiology and drug policy analysis.

What is the Defined Daily Dose (DDD)?

The Defined Daily Dose (DDD) is the assumed average maintenance dose per day for a drug used for its main indication in adults, assigned by the WHO and expressed in the drug's primary unit (mg, g, µg, or mmol). DDDs are used as a statistical unit for measuring drug consumption and comparing prescribing patterns; they do not represent recommended or prescribed doses for individual patients. The number of DDDs dispensed or prescribed divided by population and time (DDDs/1,000 inhabitants/day) provides a standardized drug utilization metric enabling cross-national and longitudinal comparisons. DDD values are published in the WHO ATC/DDD Index and are revised when new clinical evidence changes typical maintenance doses.

What are the five ATC classification levels?

ATC level 1 is the anatomical main group (14 groups, single letter), classifying by the organ or body system targeted (e.g., A = Alimentary tract and metabolism, C = Cardiovascular system, J = Anti-infectives for systemic use, N = Nervous system). Level 2 is the therapeutic main group (2 letters + 2 digits). Level 3 is the therapeutic/pharmacological subgroup (3 letters + 2 digits). Level 4 is the chemical/therapeutic/pharmacological subgroup (4 letters + 2 digits). Level 5 is the chemical substance, the most specific level, uniquely identifying each drug and route combination (5 characters + 2 digits). For example, metformin has the ATC code A10BA02 — Alimentary/antidiabetics/blood glucose lowering drugs/biguanides/metformin.

How are new drugs assigned ATC codes?

New drugs receive ATC codes through application to the WHO Collaborating Centre for Drug Statistics Methodology. Applicants submit information about the drug's pharmacological properties, therapeutic indications, and DDD. The Centre evaluates submissions and assigns provisional codes, which are published in the annual ATC/DDD Index update in January each year. Requests for new ATC codes or revisions of existing codes can be submitted by national drug regulatory authorities, pharmaceutical companies, or other interested parties. The assignment process follows documented methodology guidelines published by the WHO Centre, ensuring international consistency and alignment with the therapeutic context of actual clinical use.

How is ATC classification used in pharmacovigilance?

ATC classification is foundational to pharmacovigilance signal detection, drug utilization research, and post-marketing safety monitoring. The WHO Programme for International Drug Monitoring, operated by the Uppsala Monitoring Centre (UMC) using the VigiBase adverse event database, uses ATC codes to group reports by drug class for disproportionality analysis. Class-level safety signals can be detected across ATC-related drugs even when individual drug report volumes are insufficient for signal detection. European regulatory network studies under the IMI PROTECT and OHDSI initiatives use ATC codes to define drug exposure cohorts for population-based safety studies from electronic health records and prescription databases.