A class of diverse chemical compounds that activate cannabinoid receptors on cells that repress neurotransmitter release in the brain. Ligands for these receptor proteins include the endocannabinoids (produced naturally in the body by humans and other vertebrates), the phytocannabinoids (found in cannabis and some other plants), and synthetic cannabinoids (manufactured artificially). THC and CBD are the most notable cannabinoids, but there are at least 111 different cannabinoids isolated from cannabis, exhibiting varied effects.