The Active Pharmaceutical Ingredient (API) is the part of any drug that produces its effects. Some drugs, such as combination therapies, have multiple active ingredients to treat different symptoms or act in different ways.
All drugs are made up of two core components: the API, which is the central ingredient, and the excipient, the substance inside the drug that helps deliver the medication to your system. Excipients are chemically inactive substances, such as mineral oil. For instance, if you have a headache, acetaminophen is the active ingredient, while the liquid in the capsule or the bulk of a pill is the excipient.