Endogenous

In pharmacology, endogenous refers to a substance originating within the organism — produced by its own biosynthetic machinery — as opposed to exogenous substances introduced from outside (drugs, dietary constituents, environmental compounds). The endocannabinoid system is defined by its endogenous ligands (anandamide, 2-AG) as the physiological counterparts of exogenous plant (phytocannabinoid) or laboratory (synthetic cannabinoid) agonists. In broader biomedical language, "endogenous tone" describes the baseline activity produced by an organism's own signaling molecules, distinguishing it from effects of administered drugs. → See also: Endocannabinoid, Phytocannabinoid, Tonic signaling.