Dr. Ethan Russo is referred to by many as the pre-eminent scholar and researcher on cannabis medicine in the United States. Perhaps second in the world only to researcher Dr. Raphael Mechoulam of Israel. Here is his definition of the Entourage Effect:

Question: You refer to both THC (the “high” causer, so to speak) and CBD in the same breath. That suggests that they work together in some way. There’s this phrase, “the entourage effect” or “ensemble effect,” explain what that is in terms of the cannabis plant.

Russo: So, cannabis is a botanical. This is a way of saying that it’s a plant-based medicine. And, although the thrust of pharmaceutical development for decades has been on single molecules, often synthetic, this is the more common concept in medicine historically. What I mean is, traditionally people have used plant drugs to treat their problems. It’s only been in the last 75 years there’s been this shift toward synthetics. So, a botanical doesn’t rely on one compound to produce the beneficial effects. Rather there may be many – and that’s certainly the case in cannabis where we know that there are actually over 100 related molecules, we call cannabinoids, but in addition there are aromatic compounds, the same things that you’d find in lemon and pine needles called terpenoids that alter the effects of the cannabinoids in a way that often is synergistic. Synergy is a boosting of effect. So, it would be the idea that 2 + 2, instead of equaling 4, it gives you an 8 in terms of the benefit. So, for example, as we’ve mentioned, cannabidiol treats pain. But there are other ingredients in cannabis that also treat pain or may limit the side effects of other components and so it is sort of like an ensemble of musical instruments where you might think of THC as the soloist with an important part provided by cannabidiol, but you also have these other components producing a harmony that really increases the overall effect and hopefully makes the best possible medicine.