Hallucinnogenic Drugs alter a person's perceptions of reality and may cause hallucinations and other alterations of the senses. Drugs classified as hallucinogens include: LSD (lysergic acid diethylamide), 2,5-dimethoxy-4-methylamphetime(DOM), N,N-dimethyltrptamine(DMT), psilocin, and mescaline. There are two aspects of these drugs that classify then as hallucinogens. They all have common side effects, including distortion of sensory perception, and other psychic and somatic effects. These drugs also exhibit cross-tolerance. This means that a user of hallucinogenic drugs develops a higher tolerance to hallucinogens, the more they are used and the shorter the time span is between the last usage. Hallucinogenic drugs have been used throughout history for a number of reasons. They have been used as medicinal agents as well as having served religious purposes. Hallucinogens such as mescaline have been used in Native American ritual ceremonies. There was extensive usage of hallucinogens in the 60's and 70's as part of the counter- culture hippie movement. During the "acid tests" of this era, hallucinogenic drugs were used for mind exploration (B.L. Jacobs, "How Hallucinogenic Drugs Work"). Hallucinogenic drugs cause both physical and psychological effects on humans. The physical effects of these drugs include: dilated pupils, elevated body temperature, increased heart rate and blood pressure, appetite loss, sleeplessness, tremors, headaches, nausea, sweating, heart palpitations, blurring of vision, memory loss, trembling, and itching. A user of hallucinogenic drugs will also experience a number of psychological alterations in the brain. These drugs may cause hallucinations and illusions as well, as the amplification of sense, and the alterations of thinking and self-awareness. It is quite possible to have a bad reaction to hallucinogenic drugs. This is referred to as a "bad trip" and may cause panic, confusion, suspicion, anxiety, and loss of control. The long-term effects of these drugs can be quite dangerous. These long-term effects may include: flashbacks, mood swings, impaired thinking, unexpected outbursts of violence and eventually possibly depression that may lead to death or suicide. Quite a lot of interest concerning hallucinogens has been generated by neurobiologists and other scientists. The effects that hallucinogenic drugs have on the brain are quite complicated and very interesting. Many users of hallucinogenic drugs have experienced whole personality changes which raises questions about the relationship between brain and behavior. Scientists are also curious as to how total alterations of the senses can occur as the result of hallucinogen usage. Many people that have used hallucinogens claim to have "seen sounds" or "heard colors". Scientists ask questions such as: How can a person under the influence of hallucinogenic drugs see things that aren't there? or How do flashbacks work? Another aspect of hallucinogenic drugs that interests scientists is that they are psychomimetic meaning that they mimic certain aspects of psychosis. Through the use of hallucinogenic drugs, one can induce temporary symptoms of psychosis. As a result of the great interest in hallucinogens, many years of research have been done to try and determine exactly how the brain is affected by these drugs. Scientists have tried to determine if there is a specific site in the brain where hallucinogens act. This has been difficult to determine. Scientists still are unable to answer all questions about hallucinogenic drugs. However they have been able to determine certain areas of the brain that these drugs do act upon. Early on in the reasearch on hallucinogens, it was determined that hallucinogenic drugs structurally resemble serotonin (5-HT) Serotonin is found in specific neurons in the brain that mediate chemical neurotransmission in the brain. Neurons containing serotonin can be found in the brain stem section of the brain. Axons of