Cannabinoid Receptors and the Site of Action of Cannabinoids

duce their effects via activating cannabinoid receptors; they include the phytocannabinoids (herbal cannabinoids/natural cannabinoids found in the cannabis plant), synthetic cannabinoids, and endogenous cannabinoids (endocannabinoids) (1, 2). Cannabis, also known as marijuana, has been used as both a recreational and medicinal drug for centuries. Pain management is the most important among the medicinal purposes, and has been drawing intense attention following the discovery of cannabinoid receptors and their endogenous ligands, endocannabinoids (3-5). ∆9-tetrahydrocannabinol (THC) and cannabidiol, the critical components of the cannabis plant, and the synthetic cannabinoids and their analogues have been shown to exert strong analgesic action both in preclinical and clinical studies (6-9). In this review, after a brief introduction to cannabinoid receptors, phytocannabinoids and synthetic cannabinoids, I provide an overview of what is currently known about the synthesis, release, degradation and biological actions of endocannabinoids, regarding their role in pain modulation, and describe the recent evidence of the promising results of augmentation of endogenous cannabinoid tonus for the treatment of pain. CANNABINOID RECEPTORS AND THE SITE OF ACTION OF CANNABINOIDS