An active pharmaceutical ingredient (API) is the component of an over-the-counter (OTC) or prescription medication that produces its intended health effects. If a prescription drug has a generic, its name is the same as its API. Combination therapies have more than one active ingredient, each of which may act differently or treat different symptoms.

It's a good idea to know the APIs of medications that you take. (For example, acetaminophen—the active ingredient in Tylenol—is a well-known API.) This can help you better communicate with your healthcare providers, recognize which generics and brand name versions are the same, and avoid harmful interactions and accidental overdoses.