The Endocannabinoid System
A breakthrough in the understanding of how cannabis works in the human body occurred with the discovery of the endocannabinoid system. In the early 90’s while scientists were researching how tetrahydrocannabinol (Δ9-THC or THC) exerts its physiological effects, they discovered a new system within the human body: the endocannabinoid system. This system is composed of cannabinoid receptors on the surfaces of certain cells, and chemical compounds (ligands) called cannabinoids that bind to those receptors to exert an effect. All vertebrate animals express two types of cannabinoid receptors that are activated by either endogenous or exogenous ligands: CB1 and CB2. After it was found that THC binds to these receptors, researchers discovered endogenously produced cannabinoids that were the body’s natural ligands for these receptors.
We now know that the body's endocannabinoid system is the pathway by which THC and the other major plant cannabinoid cannabidiol (CBD) exert their effects. The CB1 receptor is found predominantly in the brain and nervous system and is the natural target of an endogenous cannabinoid called arachidonoylglycerol (2-AG). The CB2 receptor is found mainly on peripheral tissue and immune cells and its natural ligand is N-arachidonylethanolamine (anandamide or AEA). The term cannabinoid refers to a class of chemical compounds that act on CB receptors to elicit a physiological effect. There are three types of cannabinoids: endocannabinoids, plant cannabinoids (phytocannabinoids), and synthetic cannabinoids (Owens).
The first type, endocannabinoids, is made naturally by the body and works on CB receptors. They are neuromodulators, meaning that instead of affecting just one neuron across a synapse, they diffuse throughout the nervous system and affect multiple neurons (dopamine is another example of a neuromodulator). The two best understood endocannabinoids are anandamide, found primarily in the brain, 2-AG, found mainly in the rest of the body (Pacher).
The second kind, plant cannabinoids, includes over 100 varieties that have been isolated from the cannabis plant (Pacher). The plant genus Cannabis is within the plant family Cannabaceae. Three cannabis species are described: C. sativa, C. indica, and C. ruderalis, although there has been a long-standing debate among taxonomists regarding classification of these variants into species, so a biochemical method to classify cannabis variants is typically used. The primary plant cannabinoids are THC and CBD. Cannabis that has high levels of the psychoactive cannabinoid, THC, and low levels of the non/anti-psychoactive cannabinoid, CBD, is generally referred to as “marijuana,” while cannabis that has high levels of CBD and very low insignificant levels of THC is referred to as “industrial hemp,” or “hemp.”
The third type, synthetic cannabinoids, is a pharmaceutical formulation called Dronabinol (Marinol), which is prescribed for people with anorexia, weight loss in AIDS patients, and nausea/vomiting in patients undergoing chemotherapy.