UNII

A Unique Ingredient Identifier from the FDA's Global Substance Registration System — a free, public, molecular-structure-based code identifying one substance form unambiguously.

A UNII is a ten-character alphanumeric identifier issued through the FDA's Global Substance Registration System (GSRS). Unlike a catalogue number, it is defined by the substance's own characteristics — molecular structure where one is known, protein or nucleic-acid sequence where that is the defining feature — so one UNII corresponds to one substance definition.

Its precision is the useful property. Salt forms, hydrates and the free base of the same compound receive distinct UNIIs, so the identifier distinguishes material forms that a common name lumps together. The registry is public and searchable, which makes a UNII independently checkable in a way a vendor's own product code is not.

Coverage follows regulatory relevance: substances that appear in regulated products or applications are well represented, while novel research chemicals may have no UNII at all. On this site's research pages, UNIIs are published where the registry lookup verified them, alongside CAS and PubChem identifiers; the absence of a UNII on a page means no verifiable entry was found, not that the field was overlooked.

SourceFDA — Global Substance Registration System (UNII)

For research purposes only. Not for human consumption, diagnosis, treatment, or prevention of any condition. Nothing on this page is medical advice.