A cannabinoid is a chemical found in the cannabis (marijuana) plant. There are 113 cannabinoids that scientists know of, but there are likely more. Two of the best known cannabinoids are tetrahydrocannabinol (THC) and cannabidiol (CBD). THC is a psychoactive drug, meaning it can make you feel and think differently. Not all cannabinoids are psychoactive and each one works differently. All cannabinoids share a similar chemical structure and are researched for treating diseases.