There is a lot of information on the endogenous cannabinoid system -named after the plant that led to it's discovery (FYI). This is a grood article by physician Dustin Sulak DO, who breaks it down nicely.
Here is an excerpt with a link to his article.
"How can one herb help so many different conditions? How can it provide both palliative and curative actions? How can it be so safe while offering such powerful effects? The search to answer these questions has led scientists to the discovery of a previously unknown physiologic system, a central component of the health and healing of every human and almost every animal: the endocannabinoid system..."