Arachidonoyl ethanolamide (AEA) was the first endogenous cannabinoid to be isolated and characterized as an agonist acting on the same receptors (CB1 and CB2) as tetrahydrocannabinols (THC). Since that time, a number of related endocannabinoids have been isolated, most notably 2-arachidonoyl glycerol (2-AG). O-Arachidonoyl ethanolamine hydrochloride (O-AEA) is a recently isolated constituent of human and rat brain wherein the ethanolamine moiety is attached “backwards”, as an ester instead of an amide, as in AEA. O-AEA has mixed agonist/antagonist activity at the CB1 receptor and does not appear to be the native endogenous cannabinoid agonist at this receptor. This is in keeping with other observations that 2-AG is the primary endogenous CB1 receptor ligand.
