Hallucinogens are drugs that, when ingested, trigger a variety of strange and unpredictable sensations and experiences. Normally, such bizarre perceptions are experienced only in dreams, during periods of extreme emotional and physical stress, or as part of severe mental disorders such as schizophrenia.

Psychoactive Chemicals

There are dozens of different types of hallucinogens, some of which are produced naturally by plants and some of which are synthesized in laboratories or other facilities. There are many different hallucinogens used today, but the best known are mescaline and psilocybin, which come from plants, and LSD, ecstasy, and ketamine, which are manufactured in laboratories. What these drugs have in common is an ability to alter the functioning of the brain in such a way as to either modify the user's perceptions or create entirely artificial perceptions.

Users of hallucinogens experience a...