The term endocannabinoid system is commonly used to refer to the receptors, ligands, so-called endocannabinoids and the enzymes involved in their metabolism. It is named after the plant Cannabis sativa whose most important active substances tetrahydrocannabinol and cannabidiol bind to the endocannabinoid receptors. Tetrahydrocannabinol's psychotropic effects are the main reason for the popularity of cannabis, which is the most popular recreational drug in the Western world. Early scientific research focused on the effects of tetrahydrocannabinol due to its psychotropic nature. Possibly because of the toxic effects of tetrahydrocannabinol and because of the belief that tetrahydrocannabinol is the main active substance in cannabis, early research focused primarily on the effects of tetrahydrocannabinol. Only much later, with the discovery of the endocannabinoids and the myriad of functions that the endocannabinoid system performs in the mamallian body, did the focus of research slowly drift towards the endocannabinoid system itself, as opposed to the fitocannabinoids. The bodily functions which the multifarious endocannabinoid system affects include the central nervous system, gastrointestinal system and immune system. The cannabinoid receptors CB1 and CB2 are widespread throughout the human body. As such, it is difficult to target them specifically for therapeutic purpose. Hundreds of mediators are chemically related to endocannabinoids, often with similar metabolic pathways, thus the path to therapeutic relevancy is further complicated. Better understanding of the endocannabinoid system will enable researchers to discern the exact function of many key mechanisms in the human body, an thus hopefully pave the way to new therapeutic avenues.