This naming scheme is used for both the World Health Organization’s International Nonproprietary Names (INN) and the United States Adopted Names (USAN) for pharmaceuticals. In general, word stems are used to identify classes of drugs, in most cases placed word-finally. All monoclonal antibody names end with the stem "-mab". Unlike most other pharmaceuticals, monoclonal antibody nomenclature uses different preceding word parts (morphemes) depending on structure and function. These are officially called "substems" and sometimes erroneously "infixes", even by the USAN Council itself.