1. A substance added to a drug product formulation which affects the action of the active ingredient in a predictable way.

2. In immunology, a vehicle used to enhance antigenicity; e.g., a suspension of minerals (alum, aluminum hydroxide or phosphate) on which antigen is adsorbed; or water-in-oil emulsion in which antigen solution is emulsified in mineral oil (Freund’s incomplete adjuvant), sometimes with the inclusion of killed mycobacteria (Freund’s complete adjuvant) to further enhance antigenicity.


[L. ad-juvo, pres. p. -juvans, to give aid to]

Freund’s adjuvant

Freund’s complete adjuvant

Freund’s incomplete adjuvant