Cannabinoids is a group of C21 compounds present in Cannabis sativa L.. They are carboxylic acids, analogs and transformation products. They are the active ingredients found in hasish and marihuana. (-)-trans-D9-tetrahydrocannabinol (D9-THC) is the major psychopharmacologically active component of Cannabis. Cannabis affects 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. CB2 (rat 410aa, mouse 347aa, human 360aa; ~45% homology with CB1) also inhibit adenylate cyclase activity via a pertussis toxin-sensitive G-protein. Unlike CB1, CB2 does not modulate the activity of either Q-type Ca2+ or inwardly rectifying K+ channels. High level of CB2 expression was found in HL60 cells that had been differentiated into granulocytes or macrophages. It is also expressed in splenic macrophages and monocytes. It is not expressed in splenic T cells, mature blood neutrophils, thymus, liver, brain, lungor kidney. This indicates that the distribution is quite different from that of the CB1 receptor. High levels of CB2 mRNA was found in B-cells and natural killer cells, to a moderate extent in monocytes and only minimally in polymorphonuclear leukocytes, T4- and T8- cells. CNS responses to cannabinoid compounds are believed to be mediated largely by the CB1 receptor.