Active ingredients (APIs) are rarely transported alone, the other inactive ingredients are Excipients. An excipient is any component, other than the active substance(s), present in a medicinal product or used in the manufacture of the product. The intended function of an excipient is to act as the carrier (vehicle or basis) or as a component of the carrier of the active substance(s) and, in so doing, to contribute to product attributes such as stability, biopharmaceutical profile, appearance and patient acceptability and to the ease with which the product can be manufactured.

Usually, more than one excipient is used in the formulation of a medicinal product. Excipients play a central role in the development of finished pharmaceutical product (FPP) process.