Animals and psychoactive plants appear to have co-evolved, possibly explaining why these chemicals and their receptors exist within the nervous system.
Natural psychoactive drugs induce pleasure responses in humans due to human chemical-ecological adaptations to counteract the effects of plant chemical defense mechanisms.
This is in comparison with 61% (alcohol) and 7.9% (other psychoactive drugs) of the general population who use alcohol and psychoactive drugs, respectively.
