An
active ingredient (
AI) is the
ingredient in a
pharmaceutical drug or a
pesticide that is
biologically active. The similar terms
active pharmaceutical ingredient (
API) and
bulk active are also used in medicine, and the term
active substance may be used for
pesticide formulations. Some medications and pesticide products may contain more than one active ingredient. The traditional word for the API is
pharmacon or
pharmakon (from , adapted from
pharmacos) which originally denoted a magical substance or drug.