An excipient is a pharmacologically inactive substance included in a medicine to support the formulation, stability, delivery or usability of the active ingredient(s).
Unlike the active pharmaceutical ingredient (API), which produces the intended therapeutic effect, excipients perform essential functional roles such as aiding manufacturing (e.g., fillers, binders, disintegrants, coatings, lubricants), enhancing stability, improving absorption or controlling drug release. They also contribute to the medicine’s physical form, taste, and overall patient acceptability. Pharmaceutical excipients are evaluated for safety and intentionally incorporated into a drug delivery system.
Although considered inactive, some excipients may have clinically relevant properties, including the potential to cause adverse reactions in sensitive individuals, which is why regulators such as the EMA and FDA require clear labelling of certain excipients to ensure safe use. Excipients are therefore critical components of finished dosage forms, enabling the production of effective, reliable and patient-appropriate medicines.
In addition to the physical and chemical properties, the excipients used must be pharmaceutical-grade and comply with current pharmacopoeias such as Ph. Eur. (European Pharmacopoeia), USP-NF (United States Pharmacopoeia) and JP (Japanese Pharmacopoeia). The production of pharmaceutical-grade excipients also requires compliance with Good Manufacturing Practice (GMP).
See also: Drug substance, Drug product, Finished dosage form