An excipient is a substance that is added to a medication or pharmaceutical formulation alongside the active ingredient(s). Excipients are inert and do not have any therapeutic effects themselves but are included in the formulation for various purposes.

The primary function of excipients is to aid in the manufacturing process, improve stability, enhance the bioavailability of the active ingredient, modify the release profile of the medication, or improve the taste, appearance, or texture of the final product. They can also serve as fillers, binders, disintegrants, lubricants, or preservatives.

Common examples of excipients include fillers like lactose or cellulose, binders like starch or gelatin, disintegrants like croscarmellose sodium, lubricants like magnesium stearate, and preservatives like benzalkonium chloride. Excipients are carefully selected and tested for their compatibility with the active ingredient, safety profile, and their intended purpose in the formulation.

The presence of excipients in medications and pharmaceutical products is regulated and monitored to ensure their safety and efficacy. Regulatory agencies, such as the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA), have established guidelines and specifications for excipients used in pharmaceutical formulations to ensure their quality and appropriateness for use.