Drug nomenclature is the systematic naming of drugs, especially pharmaceutical drugs. Drugs, in the majority of circumstances, have 3 types of names: chemical names, the most important of which is the IUPAC name; generic or nonproprietary names, the most important of which are the International Nonproprietary Names (INNs); and trade names, which are brand names. Generic names for drugs are nowadays constructed out of affixes and stems that classify the drugs into different categories and also separate drugs within categories. A marketed drug might also have a company code or compound code.