Hallucinogenic compounds found in some plants and mushrooms (or their extracts) have been used—mostly during religious rituals—for thousands of years. While the exact ways hallucinogens affect the brain remain unclear, research suggests that these drugs work partly by temporarily interfering with chemical messengers in the brain called neurotransmitters.
Mushrooms containing the chemical psilocybin can produce LSD-like experiences, including hallucinations, an altered perception of time, and an inability to tell fantasy from reality. Panic reactions and psychosis also may occur, particularly if a user takes a large dose. There may also be long-term effects like flashbacks, impaired memory, tolerance to the drug, and risk of psychiatric illness. Find more information on LSD and PCP.