FAQs: Excipients

We will be updating this list regularly with answers to questions received from USP's stakeholders. Please contact us at excipients@usp.org if you have a question you'd like answered below.

1. What is an excipient?

Excipients are often referred to as “inactive ingredients” because, in drugs, they comprise of everything except the active pharmaceutical ingredients (APIs). Excipient functions range from helping to guarantee the stability and bioavailability of the API to the drug product’s manufacturability to its texture and taste. Excipients are a major component of almost all drugs, as well as foods, cosmetics and dietary supplements.

2. What is USP?

USP is the United States Pharmacopeial Convention – an independent, scientific nonprofit organization that sets standards for the identity, strength, quality, and purity of medicines, food ingredients, and dietary supplements manufactured, distributed and consumed worldwide. “USP” can also refer to the US Pharmacopeia, which is part of the USP-NF compendia (books, both physical and online) that contains the monographs (written identity and testing standards) for drug substances, dosage forms and compounded preparations, as well as dietary supplements and ingredients (in a separate section). Drug monographs in USP are enforceable in the United States by the Food and Drug Administration, and these standards are used in more than 140 countries.

3. What is USP-NF?

USP–NF is a combination of two compendia, the United States Pharmacopeia (USP) and the National Formulary (NF). Monographs for drug substances, dosage forms, and compounded preparations are featured in the USP. Monographs for dietary supplements and ingredients appear in a separate section of the USP. Excipient monographs are in the NF. However, if an excipient is also used as a pharmaceutical active in an FDA-approved product released in the US, its monograph will appear in the USP section instead.

4. What is included in a Monograph?

A monograph includes the name of the ingredient or preparation; the definition; packaging, storage, and labeling requirements; and the specification. The specification consists of a series of tests, procedures for the tests, and acceptance criteria. These tests and procedures require the use of official USP Reference Standards. Medicinal ingredients and products will have the stipulated strength, quality, and purity if they conform to the requirements of the monograph and relevant general chapters.

5. What is a General Chapter?

USP-NF General Chapters include detailed descriptions of tests and procedures referred to in multiple monographs.

6. What is a USP Reference Standard? How are they unique? How do I select/buy?

USP Reference Standards are highly-characterized physical specimens used in testing by pharmaceutical and related industries to help ensure the identity, strength, quality, and purity of medicines and ingredients. Materials based directly on official monographs in the USP–NF—whose standards and procedures are enforceable by the U.S. Food and Drug Administration—are recognized for use in official standards in the United States, and their use is effective in demonstrating compliance with statutory requirements.

USP Reference Standards are developed in USP labs, often through direct collaboration with industry sponsors who donate materials and methodologies. Reference Standards may be selected and purchased through the USP Reference Standard Catalog section of our website.

7. How does USP relate to the FDA IID?

The FDA’s Inactive Ingredient Database provides information on excipients present in FDA-approved drug products. Since USP’s monographs are created for drugs and ingredients present in products approved in the US, the IID provides USP with a list of potential new monographs to develop. USP works closely with the FDA to prioritize new monographs, which can be initiated in USP’s labs or, preferably, with the aid of industry partners who donate methods and materials to help create what will become approved standards.