The entourage effect is where the effects of a cannabinoid, such as CBD, are amplified when in its natural state, surrounded by the full range of compounds that naturally occur in the hemp plant.

This is why CBD oil made with pure CBD isolate tends to be much less effective than full-spectrum CBD oil. As a general rule, the more processing an oil goes through, the lower the entourage effect. CBD isolate lacks the other cannabinoids needed for optimal efficacy.