The process in which different chemical substances, including the active drug, are combined to produce a final medicinal product.

Drug formulation can result in various dosage forms, including solid, semisolid or liquid, depending on the route of administration and patient needs. Drug substances are seldom administered alone but rather they are given as part of a formulation in combination with one or more ingredients. Pharmaceutical ingredients or excipients (non-medicinal agents) serve varied and specialised pharmaceutical functions.