Cannabinoids, a group of C21 compounds present in Cannabis sativa L., their carboxylic acids, analogs, and transformation products, are the active ingredients found in hasish and marihuana. (-)-trans-D9-tetrahydrocannabinol (D9-THC) is the major psychopharmacologically active component of cannabis. Cannabis affect cognition and memory, euphoria and sedation, and antinociception (analgesia) without the respiratory depression problems associated with opioid analgesics. D9-THC is also immunosuppressive and impairs cell-mediated immunity, humoral immunity and cellular defenses against a variety of infectious agents both in vivo and in vitro. To date, two sub-types of the G-protein coupled cannabinoid receptor, CB1 and CB2, have been identified. The first brain-derived endogenous cannabinoids, an unsaturated fatty-acid ethanolamide, arachidonylethanolamide (AEA, also called anandamide) was found in brain. AEA has higher affinity for the CB1 than for the CB2.