USP Reference Standards are authentic specimens that have been approved by the USP Reference Standards Committee as suitable for use as comparison standards in USP or NF tests and assays. (See USP Reference Standards 11.) Currently official lots of USP Reference Standards are published in Pharmacopeial Forum.

Where a USP Reference Standard is referred to in a monograph or chapter, the words “Reference Standard” are abbreviated to “RS” (see USP Reference Standards 11).

Where a test or an assay calls for the use of a compendial article rather than for a USP Reference Standard as a material standard of reference, a substance meeting all of the compendial monograph requirements for that article is to be used.

The requirements for any new USP or NF standards, tests, or assays for which a new USP Reference Standard is specified are not in effect until the specified USP Reference Standard is available. The availability of new USP Reference Standards and the official dates of the USP or NF standards, tests, or assays requiring their use are announced via Supplements or Interim Revision Announcements.