Problems associated with the ATC system of drug classification.

The Anatomical Therapeutic Chemical (ATC) classification system is the international standard for drug utilisation studies. However, structural and conceptual issues remain inadequately addressed. This analysis evaluates the ATC system with respect to consistency, completeness and terminology to identify systemic weaknesses and point out potential alternatives. A systematic analysis of all 14 ATC main groups and their sublevels was conducted based on the "ATC/DDD Index 2025" and the official WHO "2025 guideline". The classification logic, coverage of therapeutic areas, handling of combination products, and terminology were examined. Discrepancies were recorded within groups and across the system as a whole. Widespread inconsistencies became apparent. Classification principles (anatomical, therapeutic, pharmacological, chemical, miscellaneous) are mixed within and across levels, causing structural incoherence. Frequent use of "X/ miscellaneous" categories highlights inadequacies in the classification logic, along with inconsistent handling of combination preparations. Drugs with multiple indications are fragmented across groups, with frequent overlaps and duplications. Terminology is often vague or outdated, obscuring pharmacological mechanisms and reflecting a historical rather than scientific rationale. Overall, the ATC system is characterised by systematic deficiencies rather than isolated irregularities. The ATC classification no longer adequately represents modern pharmacotherapy. Its reliance on single-indication logic, miscellaneous categories and outdated terminology distorts drug utilisation analyses and limits its applicability in clinical and research contexts. A mechanistically oriented system based on pharmacological properties and molecular targets would provide a more consistent, transparent and adaptable framework that is better suited to contemporary drug development, multi-indicational use and rational prescribing.