KEGG DRUG is a unified drug information resource that contains chemical structures and/or chemical components of all prescription and OTC drugs in Japan, most prescription drugs in the USA, and many prescription drugs in Europe. Thus, all the marketed drugs in Japan are fully represented in KEGG DRUG and linked to the package insert information (labels information). These include crude drugs and TCM (Tradictional Chinese Medicine) drugs, which are very popular in Japan and some of which are specified in the Japanese Pharmacopoeia. Each KEGG DRUG entry is identified by the D number distinguishing the chemical structure of chemicals or the chemical component of mixtures and crude drugs. It is associated with generic names and trade names, as well as efficacy as part of the BRITE functional hierarchies (ontologies), target information as a context of KEGG pathways, and information about the history of drug development represented as a KEGG DRUG structure map. Registration not required.