Anatomical Therapeutic Chemical Classification System

Overview
The Anatomical Therapeutic Chemical Classification System is used for the classification of drugs. It is controlled by the WHO Collaborating Centre for Drug Statistics Methodology, and was first published in 1976.

The classification system divides drugs into different groups according to the organ or system on which they act and/or their therapeutic and chemical characteristics.

Classification
In this system, drugs are classified into groups at 5 different levels:

First level
The first level of the code is based on a letter for the anatomical group and consists of one letter; there are 14 main groups:

Second level
The second level of the code is based on the therapeutic main group and consists of two digits.

Third level
The third level of the code is based on the therapeutic/pharmacological subgroup and consists of one letter.

Fourth level
The fourth level of the code is based on the chemical/therapeutic/pharmacological subgroup and consists of one letter.

Fifth level
The fifth level of the code is based on the chemical substance subgroup and consists of two digits.