Located throughout the body, are part of the endocannabinoid system, which is involved in a variety of physiological processes including appetite, pain-sensation, mood, and memory. Cannabinoid receptors are of a class of cell membrane receptors in the G protein-coupled receptor superfamily. There are currently two known subtypes of Cannabinoid Receptors, termed CB1 Receptor and CB2 Receptor. The CB1 Receptor is expressed mainly in the brain (Central Nervous System), but also in the lungs, liver, and kidneys. The CB2 Receptor is expressed mainly in the immune system and in hematopoietic cells.