GSRS, FDA's Global Substance Registration System, assigns every substance in a regulated product a Unique Ingredient Identifier (UNII). Here is how to look up a UNII, what the record tells you, and how ClinicaLister uses UNIIs to tie a molecule's trials, approvals and labels together.
The Global Substance Registration System (GSRS) was built by FDA together with the National Center for Advancing Translational Sciences (NCATS) at NIH and the European Medicines Agency to describe exactly which substances are in regulated products. It follows the ISO 11238 standard for identifying substances.
Each substance gets a UNII — a Unique Ingredient Identifier, a 10-character code such as OYN3CCI6QE (tirzepatide) or 53AXN4NNHX (semaglutide). UNIIs are used in FDA electronic product listings, which is why they appear on DailyMed labels. A UNII can be created at any point in a product's life, for anything from an atom to an organism, and having one does not mean a substance has been reviewed or approved.
GSRS classifies substances as chemical, protein, nucleic acid, polymer, structurally diverse or mixture, and records names, codes from other systems, and relationships such as salt forms and parent substances.
Two free entry points: the UNII search on precisionFDA and the public GSRS hosted by NCATS.
Open the UNII search on precision.fda.gov and type a substance name. Partial text works, so a brand, generic or code name will usually find the record.
The public GSRS at gsrs.ncats.nih.gov shows the substance's class, structure or definition, every name and synonym, codes from other systems and related substances.
Use the relationships to move between a parent substance and its salts, esters or other forms — each form has its own UNII.
precisionFDA offers downloadable lists of UNIIs, names, codes and attributes for registered substances, for bulk matching.
openFDA endpoints such as drug labels can be searched on the openfda.unii field — for example openfda.unii:"OYN3CCI6QE" returns the labels for tirzepatide products.
ClinicaLister builds its molecules on UNIIs, so a drug's FDA and EMA records, labels, NDC products and trials meet on the same identifier instead of fuzzy name matching.
Salt and parent forms are connected, so a molecule view collects its related forms and the products made from them.
Trial interventions are resolved to molecules, so a UNII leads to the clinical trials testing that substance — each link with a confidence score and provenance.
Through the ClinicaLister MCP server, Claude and other assistants can resolve a substance, its forms and its trials in plain language.
168,000+
GSRS substances with a UNII
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refresh from GSRS
9,200+
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ClinicaLister holds every public GSRS record that has a UNII; records without one are left out by design. Counts as of August–September 2026.
The Global Substance Registration System, built by FDA with NIH NCATS and the European Medicines Agency to identify the substances in regulated products. It generates the UNII codes used in FDA product listings.
A Unique Ingredient Identifier: a 10-character code that identifies one substance, for example OYN3CCI6QE for tirzepatide. It identifies the substance only and does not mean it was reviewed or approved.
Use the UNII search on precision.fda.gov or the public GSRS at gsrs.ncats.nih.gov and search by name; partial names work. precisionFDA also offers downloadable UNII lists.
The public GSRS listed 177,120 substances on October 11, 2026. ClinicaLister holds the 168,000+ of them that carry a UNII.
Each distinct substance gets its own UNII, so a salt or ester is registered separately from its parent. GSRS records the relationship between them.
Follow a molecule across every form, label and trial
Built for the Data Manager / Bioinformatician. See it in the product: Drug & Device Details. All data sources