2-Arachidonoyl glycerol-d8 (2-AG-d8) contains eight deuterium atoms at the 5, 6, 8, 9, 11, 12, 14, and 15 positions of the arachidonic acid moiety. It is intended for use as an internal standard for the quantification of 2-AG by GC- or LC-mass spectrometry. 2-AG is an endogenous agonist of the CB1 receptor. Unlike anandamide, 2-AG is present at relatively high levels in the central nervous system; it is the most abundant molecular species of monoacylglycerol found in rat brain. Formation of 2-AG is calcium-dependent and is mediated by the activities of phospholipase C and diacylglycerol lipase. 2-AG acts as a full agonist at the CB1 receptor. At a concentration of 0.3 nM, 2-AG induces a rapid, transient increase in intracellular free calcium in NG108-15 neuroblastoma X glioma cells through a receptor-dependent mechanism.