Certain types of mushrooms and datura plants are also hallucinogens. These drugs are injected, taken orally, or eaten. Hallucinogens produce radical changes in the mental state, involving distortions of reality and acute hallucinations. Hallucinogens have no prescribed medical use and are made and sold illegally. Tolerance may occur rapidly from the use of hallucinogens.
Hallucinogens cause cross-tolerance.
This means that the use of one hallucinogen causes and increases tolerance to other hallucinogens. A dependence on hallucinogens is likely, but no withdrawal symptoms occur when use of the drug is discontinued. Serious mental illness may occur. Hallucinogens may be used by those who mistakenly hope to attain transcendental, mystical experiences, which they believe will provide them with a greater understanding of life. Some people may remain permanently brain damaged or psychotic from the drugs and this condition cannot be reversed.