The term substrate typically refers to a molecule (some drug or chemical) upon which an enzyme acts. When a substrate reacts with an enzyme, a chemical reaction - like a metabolic reaction - occurs and the substrate is transformed into one or more new and/or different chemical products. In a metabolic reaction, these products are usually the metabolites formed. Sometimes, when multiple drugs that are all substrates of the same enzyme are administered into the human body, a state of competition may occur when these substrates compete for the same binding or interaction with the same enzyme.