The main psychoactive compound found in psilocybin mushrooms is called psilocin. It is a serotonin receptor agonist that causes the release of serotonin in the brain. Serotonin is a neurotransmitter that helps control many bodily functions such as mood, appetite, sleep and motor coordination. By stimulating serotonin receptors, psilocin can have a calming effect on the user. Because of this, it is often used for anxiety reduction, stress relief and as a sleeping aid. It is also sometimes used to help people quit smoking.