Drug Class Browser

Browse medications organized by WHO ATC drug classification system. Explore drug classes, see related medications, and understand class-based side effects.

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WHO ATC Drug Classification

The Anatomical Therapeutic Chemical (ATC) classification system, maintained by the WHO Collaborating Centre for Drug Statistics Methodology, organizes drugs into groups according to the organ or system on which they act and their therapeutic, pharmacological, and chemical properties.

The hierarchy has five levels: Anatomical main group (e.g., A: Alimentary tract and metabolism), Therapeutic subgroup, Pharmacological subgroup, Chemical subgroup, and Chemical substance. ATC codes are used worldwide for drug utilization research and prescribing guidelines.

Understanding drug classes helps patients recognize that medications in the same class share mechanisms of action, similar side effect profiles, and potential cross-reactivity. This knowledge is important when switching medications or checking for class-level contraindications.

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Medical Disclaimer

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
Navigate the WHO ATC hierarchy
Begin at the ATC anatomical main group level (e.g., A for alimentary tract, C for cardiovascular) and drill down through therapeutic, pharmacological, and chemical subgroups to explore the complete ATC classification tree. The WHO ATC/DDD Index 2024 is the reference standard for classification.
2
View drugs within a class
Select any ATC subgroup to display all FDA-approved drugs classified within it, including both brand and generic names, along with key pharmacological attributes such as mechanism of action, approved indications, and common adverse effects characteristic of the class.
3
Compare class-specific side effects
Review the adverse effect profile shared by drugs in the same class, reflecting their common mechanism of action. Class-level side effects — such as myopathy risk with statins, hyperkalemia with RAASi agents, or QT prolongation with antiarrhythmics — apply across members and inform therapeutic substitution decisions within the class.

About

Drug class organization is fundamental to pharmacology education, clinical prescribing, and pharmacovigilance. The WHO Anatomical Therapeutic Chemical classification system provides a globally standardized hierarchical framework for categorizing drugs by anatomical target, therapeutic purpose, pharmacological mechanism, and chemical structure. This five-level taxonomy enables consistent international comparison of drug prescribing patterns, supports pharmacoepidemiology research, and provides the organizational backbone for national formularies and clinical decision support systems.

Understanding drug classes enhances clinical reasoning in several important ways. First, knowledge of class mechanisms predicts adverse effect profiles, enabling clinicians to anticipate risks when prescribing and patients to recognize class-related symptoms. Second, class-level contraindications apply broadly across members: a documented allergy to one sulfonamide antibiotic, for example, raises concern about cross-reactivity within the class and with structurally related non-antibiotic sulfonamide derivatives used in diuretics and hypoglycemics. Third, class awareness supports formulary management and therapeutic substitution decisions when preferred agents are unavailable or not tolerated.

This drug class browser implements the WHO ATC hierarchy to enable hierarchical exploration of the pharmacological landscape, from broad anatomical categories down to individual chemical substances. Each class node displays drugs grouped at the appropriate ATC level along with their shared pharmacological attributes and class-characteristic adverse effects. The integration of class-level adverse effect data — such as angioedema risk with ACE inhibitors, nephrotoxicity risk with aminoglycosides, or Steven-Johnson syndrome risk with aromatic anticonvulsants — reflects the standard approach used in clinical pharmacology education and in structured product labeling guidance issued by FDA and ICH.

FAQ

What is the WHO ATC/DDD classification system?

The WHO Anatomical Therapeutic Chemical (ATC) and Defined Daily Dose (DDD) classification system is a global drug classification standard maintained by the WHO Collaborating Centre for Drug Statistics Methodology in Oslo. The ATC system classifies drugs at five levels: anatomical main group, therapeutic main group, therapeutic/pharmacological subgroup, chemical/therapeutic/pharmacological subgroup, and chemical substance. The DDD is the assumed average maintenance dose per day for a drug used for its main indication in adults, providing a standard unit for drug utilization comparisons across countries, time periods, and healthcare settings.

How do class effects differ from individual drug effects?

A class effect is an adverse reaction or therapeutic property attributable to the shared mechanism of action across all drugs in a class, regardless of individual molecular differences. For example, all statins (HMG-CoA reductase inhibitors) carry a class risk of myopathy and rhabdomyolysis because they all inhibit cholesterol synthesis in muscle as well as liver tissue. In contrast, drug-specific effects arise from individual pharmacokinetic properties, off-target receptor binding, or metabolic pathways not shared by all class members. Simvastatin's higher myopathy risk at maximum doses compared to rosuvastatin reflects a drug-specific rather than class-wide effect.

Why is drug class important for drug substitution?

Drug class information is critical for therapeutic substitution — replacing one drug with another within the same class when a patient cannot use the originally prescribed agent due to allergy, intolerance, formulary restrictions, or cost. Regulatory and clinical guidelines generally support therapeutic substitution within classes when drugs have similar mechanisms, comparable efficacy data, and manageable differences in pharmacokinetic profiles. However, not all class members are interchangeable; differences in receptor subtype selectivity, bioavailability, renal vs. hepatic elimination, and approved indications can affect substitution appropriateness for specific patient populations.

How does the ATC classification relate to pharmacological mechanism?

The ATC third and fourth levels represent pharmacological and chemical subgroups and generally align with mechanism of action. For example, ATC level 3 code C10A groups all lipid-modifying agents, while level 4 distinguishes between HMG-CoA reductase inhibitors (C10AA), fibrates (C10AB), bile acid sequestrants (C10AC), and PCSK9 inhibitors (C10AX). This hierarchical structure allows drug utilization researchers and pharmacoepidemiologists to compare related agents at varying levels of specificity. However, the ATC is a statistical tool for comparison and drug utilization measurement, not a pharmacological taxonomy designed for clinical decision support.

Are drug classes consistent across international regulatory systems?

Drug classification terminology varies between regulatory systems, though there is substantial overlap. The WHO ATC system is internationally recognized and used by EMA, Health Canada, TGA (Australia), and most national medicines agencies. FDA uses Established Pharmacologic Class (EPC) terminology in approved labeling, which aligns with but is not identical to ATC nomenclature. The NDF-RT (National Drug File Reference Terminology) and RxNorm systems used in US electronic health records provide additional classification layers. For cross-national drug utilization comparisons, the WHO ATC/DDD system is the most widely adopted standard.