The term hallucinogen literally means producer of HALLUCINATIONS. A variety of drugs and medicines as well as various disease states can lead to the development of hallucinations. They can occur during a high fever, after acute brain injuries, or as part of a DELIRIUM, accompanied by confusion in judgment, intellect, memory, emotion, and level of consciousness. The patient is said to be "out of it"—not in touch with reality. In fact, many infections affecting the brain, conditions that disrupt the availability of nutrients essential for brain function, or direct brain injury can cause transient or prolonged delirium. Disease states not directly involving the brain also can alter brain function. For example, the overproduction of thyroid or adrenal hormones in endocrine disease can cause psychotic mental symptoms. In addition, poisoning or other toxic reactions can produce hallucinations.

Some drugs used to treat certain illnesses, although not prescribed for...