Standards
Unique Ingredient Identifier (UNII)
An FDA-assigned identifier for a substance based on its defined identity.
- Kind
- Identifiers
- Steward
- U.S. Food and Drug Administration, Global Substance Registration System (GSRS)
What it describes
A UNII identifies a substance in the FDA's Global Substance Registration System. It supports consistent references to ingredients across product listings and other regulatory data. The identifier is tied to a defined substance identity, which may be more precise than a common name. Names and synonyms should therefore be treated as searchable descriptions, not as substitutes for a verified substance record.
FDA states that a UNII can be generated at any point in a substance's regulatory life cycle. Its existence does not imply FDA review, approval, safety, or use in a marketed product. A record that links a UNII to a product should retain separate evidence for formulation, strength, manufacturer, and regulatory status. Distinct salts or forms may require distinct substance identities.
Useful for
- Reconcile ingredient names and synonyms.
- Link substance references across FDA data.
- Distinguish specific substance identities.
Limits
- Does not imply regulatory approval.
- Does not identify a finished product.
- A common name can cover distinct substance forms.
How it is used in practice
Drug labels, ingredient lists and substance registries all name the same chemical or biological entity in different words: a systematic name, a nonproprietary name, a brand-adjacent synonym, a salt form. A UNII gives each defined substance one identifier, so that an ingredient listed in a product label can be joined to the same substance in other FDA data and in public resources that cross-reference it. FDA's Global Substance Registration System generates the identifier, and the public search tools let anyone look up a substance by name, code or related identifier.
The registry follows an international model for describing substances, and the GSRS software is open for other organizations to use. For a system of record this means that the substance identity, the names attached to it and its cross-references to other identifier systems can be retrieved from a source with a stated steward, instead of being inferred from strings.
A worked example
A fictional product, Haldenamab Injection, lists its active ingredient as the hydrochloride form of a fictional small molecule on its label. A competitive-intelligence team compares it with a trial record that names the base compound. A string match fails because the names differ.
The team looks up both names in the substance registry and finds two distinct substance records, one for the salt and one for the base, each with its own UNII. The registry shows the relationship between them. The statement recorded is that the label and the trial refer to related but distinct substances, citing both registry entries and the date of the lookup. A claim that the trial tested the labelled product's active ingredient would need the trial's own description of the investigational product, because the registry shows identity and relationship, not what a trial administered.
Evaluating a claim that rests on a UNII
A UNII answers the question of which substance. It does not answer questions of approval, safety, quality or marketing status. FDA states that a UNII can be generated at any point in a substance's life cycle, so its existence does not signal that a regulator has reviewed the substance. A claim that a product contains a given substance should cite the product label or listing for the ingredient and the registry for the substance identity, and keep the two sources distinct.
Check the grain. Registry entries distinguish salts, hydrates, stereoisomers and, for biological products, defined structural descriptions. Collapsing them to a parent substance simplifies analysis and loses the information on which a formulation claim may depend. If the analysis needs a simplification, record that it was applied and by what rule, so the original identities can be recovered.
Confusions to avoid
A UNII is not a CAS Registry Number, a product code or an NDC. A CAS number is assigned by a chemical-abstracts service and has its own coverage and licensing. An NDC identifies a listed drug package. A UNII identifies a substance and can be linked to the others, but the link is a statement from the registry that has a date.
The identifier is also non-semantic: nothing in the characters describes the substance, so a UNII copied between systems cannot be checked by reading it. Verification means looking the code up in the registry and comparing the returned name, structure or description with the claim. Store the lookup date, because names and cross-references are curated and can be corrected.
Questions a reviewer can ask
Does the substance record found by the UNII match the name, structure or description in the claim? Does it identify the active moiety, a salt or a hydrate, and is that the level the claim needs? Which product source shows that the substance is in the product? When was the registry read, and have names or links been revised since? If a parent substance was used for grouping, where is the rule that says so?
Related terms
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Enquiry
Which of your sources carry Unique Ingredient Identifier (UNII)?
Tell us which sources carry it, which key the same entity some other way and who may read which. We reply with whether and how a first record would use this identifier.
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