For Industry

Substance Registration System - Unique Ingredient Identifier (UNII)

The overall purpose of the joint FDA/USP Substance Registration System (SRS) is to support health information technology initiatives by generating unique ingredient identifiers (UNIIs) for substances in drugs, biologics, foods, and devices. The UNII is a non- proprietary, free, unique, unambiguous, non semantic, alphanumeric identifier based on a substance’s molecular structure and/or descriptive information.

The procedures and management of the SRS is provided by the SRS Board. The SRS Board includes experts from both FDA and USP. The SRS operating procedures defined by the SRS Board are detailed in the SRS Manual.

The UNII is:


  • One of the core components of the United States Federal Medication Terminology.
  • Used in the FDA's Structured Product Labeling
  • Used to assist in the generation of the National Library of Medicine's (NLM's) RxNorm.
  • A US government standard for drug ingredient and food allergen identifiers
  • A component of the Environmental Protection Agency's Substance Registry System (future)


The UNII may be found in:


  • NLM's Unified Medical Language System (UMLS)
  • National Cancer Institutes Enterprise Vocabulary Service
  • USP Dictionary of USAN and International Drug Names (future)
  • FDA Data Standards Council website
  • VA National Drug File Reference Terminology (NDF-RT)
  • FDA Inactive Ingredient Query Application


Questions about the UNII should be directed to



SRS Resources

FDA Substance Registration System User's Guide Version 5c

UNIIs, Preferred Substance Names, and their Identified Synonyms - Download the latest release of the UNIIs, Preferred Substance Names, and their Identified Synonyms - this file contains all publically available UNIIs along with new and changed terms since the previous release. The synonyms list is incomplete but is provided to assist in the process of identifying UNIIs and Preferred Substance Names (e.g., for Structured Product Labeling submissions).

UNII Definitions Exchanged in SPL Formatdisclaimer icon

Substance Registration System – Unique Ingredient Identifier (UNII) Presentation - CAPT. William A Hess, FDA

Page Last Updated: 03/27/2018
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