Psilocybin, however, is too large of a molecule to pass into the brain, but when the liver metabolizes it, psilocybin is converted into psilocin, which is able to pass into the brain.
Psilocin stimulates the neurotransmitter serotonin, which controls many aspects of our body, including mood, memory, and appetite. Because psilocin stimulates the Type 2 serotonin receptor, hallucinations are common. Another cause for hallucinations by psilocin is by the inhibition of the raphe cells (cells in the brain that control vision and emotion). This inhibition causes a type of sensory overload which is responsible not only for hallucinations, but also for the amplification of emotions experienced by users of hallucinogenic mushrooms.