SYSTEMIC definition: 1. A systemic drug, disease, or poison reaches and has an effect on the whole of a body or a plant…. Learn more. Systematic and systemic both come from system. Systematic is the more common word; it most often describes something that is done according to a system or method. Systemic describes what relates to or affects an entire system, be that system physical, organizational, or societal. Systemic chemicals or drugs are absorbed into the whole of an organism such as a plant or person, rather than being applied to one area. SYSTEMIC definition: of or relating to a system, especially when affecting the entirety of a thing. See examples of systemic used in a sentence. “Systemic” means affecting the entire body rather than a single spot. In medicine, a systemic condition, treatment, or reaction is one that travels through your bloodstream and reaches tissues and organs throughout your body, as opposed to staying in one localized area. But what does it really mean when we say something is systemic by nature? By one definition it is, “Of or relating to a system or a system and other relating to or affecting the entire body or an entire organism.” In medicine, systemic means affecting the whole body, or at least multiple organ systems. It is in contrast with topical or local.