The pharmacological actions of THC result from its binding to the cannabinoid receptor CB1, located mainly in the central nervous system, and the CB2 receptor, mainly present in cells of the immune system. It acts as a partial agonist on both receptors, i.e., it activates them but not to their full extent. The psychoactive effects of THC are mediated by its activation of the CB1 receptor, which is the most abundant G protein-coupled receptor in the brain.