Anatomical Therapeutic Chemical (ATC) Classification

Medicinal substances frequently have several ATC codes for various routes of administration with different therapeutic uses, for example products that contain prednisolone as a single ingredient have eight different ATC codes according to the indication (systemic and various local application formulations).
A few medicinal substances have different ATC codes assigned for different strengths of the pharmaceutical formulation. For example, low strength finasteride tablets used for treatment of baldness are classified under D11AX Other dermatologicals and the high strength tablets used for benign prostatic hyperplasia (BPH) are classified under G04C Drugs used in BPH.

The challenge occurs when a medicinal product (same strength and route of administration) is approved and used for two or more equally important indications, and the main therapeutic use differs from one country to another. This will often give several classification alternatives and the main indication is decided by the WHO International Working Group for Drug Statistics Methodology on the basis of available literature and a qualified assumption of the most prevalent indication worldwide. Such drugs are usually only given one code and this may be a problem for users in countries where other uses are predominant.

Medicinal products containing two or more active ingredients are regarded as combinations in the ATC classification system and given different ATC codes from the product with a single component (one active ingredient).