1. An active ingredient is any ingredient that provides biologically active or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease or to affect the structure or any function of the body of humans or animals. The similar terms active pharmaceutical ingredient (abbreviated as API) and bulk active are also used in medicine. The term active substance may be used to describe the effective chemical used to control bacteria or pests. Some medication products can contain more than one active ingredient. The traditional word for the active pharmaceutical agent is pharmacon or pharmakon (from Greek: φάρμακον, adapted from pharmacos) which originally denoted a magical substance or drug. The terms active constituent or active principle are often chosen when referring to the active substance of interest in a plant (such as salicylic acid in willow bark or arecoline in areca nuts), since the word "ingredient" can be taken to connote a sense of human agency (that is... from wikipedia.org