Here’s what we do know: The cannabis plant contains a wide variety of chemical compounds, many of which fall under the broad category of cannabinoids. There are more than 100 — exactly how many, we’re not sure. The best-known and certainly most profitable are tetrahydrocannabinol (THC) and cannabidiol (CBD). Both of these compounds stimulate the same receptor in the brain, called CB1, but have differing effects on the brain. Researchers aren’t totally sure why.