The Endocannabinoid System is a complex regulatory system made up of receptors, molecules called endocannabinoids, and enzymes that either synthesize or metabolize those endocannabinoids. The main function of the endocannabinoid system is to regulate the human body by maintaining homeostasis.
The cannabis plant produces more than 500 different chemical compounds, including over 120 phytocannabinoids (like THC and CBD), 30 (known) terpenes (like linalool and myrcene), flavonoids and hundreds of other compounds; but fewer than 50 of these compounds are produced in significant amounts.
CB1 receptors are found primarily in the nervous system while CB2 receptors are found predominately the immune system, however both receptors can be found in various organs throughout the body. The mapping of these receptors fits well with the diverse range of symptoms and conditions that are found to respond positively to medicinal cannabis, and the synergistic effect (known as the Entourage Effect) of these different compounds working together in each unique strain/medicine is what causes such diverse effects.