The use of hallucinogens, such as psilocybin, has actually been a part of human society for many generations in certain cultures. Before there was a more comprehensive, scientific understanding of neurons, the structure of the brain, or nervous system stimulation, the properties of certain plants such as cacti containing peyote, or mushrooms with psilocybin were considered spiritual.
Today, we have a much clearer, more technical and scientific understanding of how these narcotics work. In the 20th century, we have even found laboratory methods to synthesize and magnify these properties into new, more powerful drugs. PCP, and, more commonly, lysergic acid diethylamide, or LSD, are drugs that are commonly manufactured, sold and used for their ability to cause users to experience a dramatically different world of sensation from what they are used to in their everyday world. So despite our increased knowledge of how these narcotics work, people can still use, abuse and become addicted to them, requiring treatment for hallucinogens to overcome this addiction.