The component of a medication that does the work, for example, semaglutide is the API inside Wegovy and Ozempic. Everything else in the product (stabilizers, preservatives, liquid) is an inactive ingredient, or excipient. With compounded drugs, where the API is sourced and whether it's the exact same molecule as the branded version is a key safety question.
Related terms: Excipient · Salt form (semaglutide sodium / acetate) · Compounded medication · Semaglutide