The Unique Ingredient Identifier (UNII) is a non-proprietary, free, unique, unambiguous, non-semantic, alphanumeric identifier linked to a substance's molecular structure or descriptive information by the Substance Registration System (SRS) of the Food and Drug Administration (FDA) and the United States Pharmacopeia (USP).
The SRS is used to generate permanent, unique identifiers for substances in regulated products, such as ingredients in drug and biologic products. The SRS uses molecular structure and descriptive information to define a substance and generate the UNII. The primary means for defining a substance is by its molecular structure as represented on a two-dimensional plane. When a molecular structure is not available (e.g., botanicals), the UNII is defined by descriptive information.