Pharmacopoeias are authoritative treatises on drugs and preparations, their description, formulation, analytic composition, physical constants, main chemical properties used in identification, standards for strength, purity, and dosage, chemical tests for determining identity and purity, etc. They are usually published under governmental jurisdiction. They differ from formularies in that they are far more complete; formularies simply list drugs or collections of formulas for the compounding of medicinal preparations. However, sometimes the terms "pharmacopoeia" and "formulary" are used interchangeably.
In addition to serving as current reference sources, pharmacopoeias and formularies provide an historical record of pharmacy practice, drug use, and drug availability.
NLM collects the national pharmacopoeias of the world insofar as possible. Other formularies are more selectively acquired, with emphasis on those likely to be of historical interest. Hospital formularies, which list all drugs commonly stocked in a hospital pharmacy, generally are not collected.