abstract:The UNique Ingredient Identifier (UNII) is a non-proprietary, free, unique, unambiguous, non-semantic, alphanumeric identifier linked to a substance's molecular structure and/or descriptive information by the Substance Registration System of the Food and Drug Administration (FDA). A UNII is always ten characters long, and is randomly generated, so as not to contain any inherent information on time of entry or type of substance.