Why is that the case that the effects are so different between different people and even for the same person on different days? As usual, when looking at things in more detail, they are more complicated than they appear at first sight. In the case of marijuana and sleep, we need to understand that there is more than one chemical in the cannabis plant which affects the human brain, and there is more than one part of the human brain which reacts to these chemicals. An interesting contrast in terms of the effect of cannabis on sleep exists between the main psychoactive compound of marijuana, tetrahydrocannabinol (THC), and the non-psychoactive cannabidiol.