Known as API, Active Pharmaceutical Ingredient is the part of any drug that is active. Some drugs are comprised of multiple active ingredients to treat different diseases. There are two core components in any drug: the API, or Active Pharmaceutical Ingredient, is the central ingredient; and the excipient, is the substance inside the drug or tablet which helps deliver the medication to your system. It is the API that produces the desired effect in the body, while the excipients are not chemically active, such as mineral oil.