Active Pharmaceutical Ingredient or API is the chief therapeutic entity in a drug product. Simply put, that part of the drug product, which is responsible for its curative action is API. If a consider an example – in a Crocin brand tablet, Paracetamol 500 mg is actually the API (the powder which is responsible for the tablet’s power to cure fever). But actually, the tablet contains a lot more than just 500 mg of paracetamol. They may be some colorants, binders, fillers, preservatives, etc. as well in the tablet, apart from paracetamol. All these materials together are termed’Excipients’. So API (paracetamol) in combination with excipients (binders, fillers, colorants, etc.) constitutes any finished drug product (tablets, capsules, syrups, etc.)