The hemp and cannabis plants contain over 120 distinct compounds, the two most abundant and well-researched of which are CBD and THC. CBD is skyrocketing in popularity throughout the United States, and THC is also growing in popularity due to shifting legislation (as states move away from prohibition and towards full legalization), it is important to bear in mind that clinical studies have consistently demonstrated the greater efficacy of full spectrum extracts.
In other words, research strongly suggests that CBD seems to work significantly better for the majority of users when it contains the entire host of phytocannabinoids naturally found in the plant. This research indicates that although people frequently consume THC and CBD in isolated compounds (known respectively as THC distillate and CBD Isolate), they can likely derive substantially more benefit by utilizing these two compounds together — along with the smaller, organic compounds found in the plant, which are known as terpenes; all of these myriad components of the plant come together to produce the entourage effect.
It has been theorized (based on a significant and mounting body of evidence) that THC (in particular), plays a critical role in in opening up cannabinoid receptors when it is administered along with CBD. In addition to promoting overall wellness, CBD is often used to address symptoms such as anxiety, stress, nausea and pain. CBD does not act by treating any of these specific conditions directly, but instead works to restore homeostasis to neurological and immunological pathways. Full Spectrum CBD has demonstrated greater efficacy in this regard, and scientists believe that this owes to something called the Entourage Effect.
The Entourage Effect refers to the synergistic action of different cannabinoids, flavonoids, lipids, and terpenes when they are all acting in concert on receptors within the endocannabinoid system. Cannabinoids act on CB1 and CB2 receptors found throughout the body. CB1 receptors are primarily found in the brain and Central Nervous System, whereas CB2 receptors are generally found within the immune system and organs related to it. The additional compounds within the plant (such as its terpenes) also play a role in regulation of the endocannabinoid system.
A great deal of CBD products currently on the market are made from CBD isolate, so they only contain CBD. Full spectrum CBD products — which retain multiple cannabinoids in addition to other components of the plant, such as terpenes and fatty acids — are beginning to grow in popularity as understanding of the entourage effect becomes more widespread. The other cannabinoids within the hemp/cannabis plant (particularly THC) seem to play an integral role in assisting the body in opening up the cannabinoid receptors, thus maximizing CBD’s therapeutic benefits.
The Entourage Effect was first theorized in 1998 by two well-respected Israeli scientists, Dr. Shimon Ben-Shabat and Dr. Raphael Mechoulam. They published their findings in the European Journal of Pharmacology that year. In a paper titled: “An entourage effect: inactive endogenous fatty acid glycerol esters enhance 2-arachidonoyl-glycerol cannabinoid activity,”  they posited that fatty acids occurring naturally in the cannabis plant significantly enhanced cannabinoid activity within the body.
In 2009, the Entourage Effect was further elaborated by scientists H. Wagner and G. Ulrich-Merzenich. Their study defined the four primary mechanisms of the Entourage Effect as: “The ability to affect many different targets and areas of the body; the ability to improve the active absorption of the active ingredients by the body; the ability to better overcome bacterial defense mechanisms and the ability to minimize adverse side effects.” 
There is still a great deal of research to be done in this arena, as we are only finally beginning to understand one of nature’s most important botanical gifts. Eventually, science will illuminate the exact manner by which these compounds interact with the receptors of the human body — and perhaps even more importantly, in what doses they compliment each other most effectively. For now, one thing seems rather certain: the majority of CBD users prefer full spectrum extracts, and the “entourage effect” provides a solid, scientific explanation for the strength of that preference.