Pharmaceutical Drug substance (API) and Drug Product

What is Definition of Drug substance (API)?

“An active pharmaceutical ingredient (API) is a substance which is used in the preparation of a drug product. API and excipients (inert materials) together form a drug product which is used for the treatment of diseases in human beings. The API is also called as a drug substance.”

ICH definition of an Active Pharmaceutical Ingredient (API)

Any substance or mixture of substances intended to be used in the manufacture of a drug (medicinal) product and that, when used in the production of a drug, becomes an active ingredient of the drug product. Such substances are intended to furnish pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease or to affect the structure and function of the body.

US FDA definition of an Active Pharmaceutical Ingredient (API)

"Active Pharmaceutical Ingredient (API) (or Drug Substance): Any substance or mixture of substances intended to be used in the manufacture of a drug (medicinal) product and that, when used in the production of a drug, becomes an active ingredient of the drug product. Such substances are intended to furnish pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease or to affect the structure and function of the body".

European Medicines Agency definition of an Active Pharmaceutical Ingredient (API)

Active Pharmaceutical Ingredient (API) (or Drug Substance) are the substances those are responsible for the activity of medicines.