An Active Pharmaceutical Ingredient (API) is a substance that is intended to be used in the manufacturing of a drug product and which, when administered to a patient, becomes an active ingredient in the medication. It is the molecular entity that exerts the desired pharmacological activity. APIs can be derived from various sources, including natural resources, chemical synthesis, or biotechnological processes. The characteristics of APIs, including their purity, potency, stability, and solubility, play a pivotal role in determining the efficacy of a drug product.