The USAN Council’s goal is to provide meaningful designations for compounds, enhancing prescribing and patient safety. Excessive stem creation diminishes the usefulness of the system. Therefore, the council strives to use existing stems whenever possible. For a new stem to be assigned, the burden of proof falls on the applicant to show it is warranted. If, in the opinion of the council, substantial data shows a substance is unique and cannot fit existing nomenclature, a new stem may be coined.
The listing of USAN stems (XLSX) represents common stems for which chemical and/or pharmacologic parameters have been established. These Council-approved stems and their definitions are recommended for use in coining new nonproprietary drug names belonging to an established series of related agents.
USAN appropriately incorporates this established class stem system. By doing so, similar compounds maintain a common "family" name that provides immediate recognition.
The list is not exhaustive. It does not include all stems used by the council and other national or international nomenclature groups. It is the nature of the nomenclature process that new, potential stems are constantly being created and that definitions of older stems may need to be modified as new information becomes available.
New USAN stems (PDF) that received official approval at the July 2016 USAN Council meeting.