Excipient

An excipient is an ingredient in a formulation that is not the active - it does not produce the product's primary effect, but performs some other necessary function. The term is most common in pharmaceutical and personal care manufacturing, though the concept applies to formulated products generally.

Calling excipients inactive is slightly misleading. They carry the active and control how it is delivered, stabilise the product against degradation, control viscosity and texture, preserve it against microbial growth, and give it acceptable colour and appearance. A product with the correct active concentration and the wrong excipient system may not work at all.

Excipients typically make up the great majority of a formulation by weight, so they are where most of the physical properties come from and often where meaningful cost reduction is found. They are also less tightly specified than actives - though not unspecified, since grade and supplier changes can alter product behaviour more than expected.

Where excipients cause trouble is in reformulation. A substitution intended to save cost or replace a discontinued material can change stability, appearance or feel, which is why substitutions need validating rather than simply approving on paper - see raw-material substitution and stability testing.

Excipients are where cost reduction is usually found, but changes need validating rather than approving on paper. Ask what testing a proposed substitution would involve before agreeing to it - the saving is sometimes smaller than the qualification work.

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