Hallucinogens are substances that, when ingested, cause hallucinations, which are perceptions of things or feelings that have no foundation in reality.

Hallucinogens, or psychedelics, are substances that alter users' thought processes or moods to the extent that they perceive objects or experience sensations that have no basis in reality. Many natural and some synthetic substances have the ability to induce hallucinations. A ready market exists for such chemicals, and they are manufactured in illegal chemical laboratories for sale as hallucinogens. LSD (lysergic acid diethylamide) and many so-called designer drugs have no useful clinical function and are considered recreational drugs. These drugs are dangerous.

Hallucinogens have long been a component in the religious rites of various cultures, both in the Old and New Worlds. Among the oldest are substances from mushrooms or cacti that have been in use in Native American rites since before recorded history. Hallucinogenic mushrooms have been used for centuries in rites of medicine men to foresee the future or to communicate with so-called higher powers. Hallucinogenic mushrooms are consumed by either eating them directly or by drinking a beverage in which the mushrooms have been boiled. The effects are similar to those experienced with the use of LSD: enhancement of colors and sounds; introspective interludes; perception of nonexistent or absent objects or persons; and sometimes terrifying, ominous visions.

Another ancient, natural hallucinogenic substance is derived from the Mexican peyote cactus. The flowering head of the cactus contains a potent alkaloid called mescaline. In addition to mescaline from peyote, hallucinogenic substances can be found in a number of other plant species.

In the 1960s, people involved in the hippie movement discovered and embraced hallucinogens and incorporated them into the culture. Artists, poets, and writers during that time believed that the use of hallucinogens enhanced their creative prowess. LSD was a well-known hallucinogen. Its use declined after large numbers of users experienced serious, sometimes fatal, effects during this era. The U.S. Controlled Substance Act of 1970 classified LSD as a Schedule I drug, a designation reserved for those drugs considered unsafe, medically useless, and associated with a high potential for abuse.

Magic mushrooms.

Magic mushrooms.
(© George Post/Science Source/Photo Researchers, Inc.)

LSD had its start in 1938, when Swiss chemist Dr. Albert Hofmann (1906–2008) first synthesized the drug while seeking a headache remedy. Years later, he accidentally ingested a small, unknown quantity, and shortly afterward he was forced to stop his work and go home. Hofmann lay in a darkened room and later recorded in his diary that he was in a dazed condition and experienced “an uninterrupted stream of fantastic images of extraordinary plasticity and vividness … accompanied by an intense kaleidoscope-like play of colors.”

Three days later, Hofmann purposely took another dose of LSD to verify that his previous experience was the result of taking the drug. He ingested what he thought was a small dose (250 micrograms) but which was actually about five times the amount needed to induce pronounced hallucinations in an adult male. His second hallucinatory experience was even more intense, and his journal describes the symptoms of LSD toxicity: a metallic taste, difficulty breathing, dry and constricted throat, cramps, paralysis, and visual disturbances.

LSD is one of the most powerful hallucinogens. The so-called acid trip results when users swallow the drug, smoke it (usually with marijuana), inject it, or rub it on the skin. A common method of drug ingestion is to lick the back of a homemade stamp on which LSD has been deposited. The drug dissolves in the user's saliva. When taken by mouth, the drug begins to take effect in about 30 minutes, with its full effect following in about another 30 minutes and lasting for two to four hours. Regardless of the method of ingestion, LSD is a dangerous drug, and because even a tiny amount can produce strong effects, overdoses are common.

The physiological effects of LSD include:

LSD users may salivate excessively and shed tears, and the hair on the back of their arms may stand erect. Pregnant women who use LSD or other hallucinogens may have a miscarriage, because these drugs cause the muscles of the uterus to contract and possibly expel the fetus.

To the observer, LSD users typically appear quiet and introspective and often are unwilling or unable to interact with others or to carry on a conversation. Even moderate doses of LSD can have profoundly disturbing effects on individuals, including terrifying psychological impacts.

Other effects of LSD use include:

A person who takes LSD steadily with the doses (a dose is usually 50–100 micrograms) close together can develop a tolerance to the drug. That is, the amount of drug that once produced a pronounced high no longer is effective, and this may cause the user to seek larger doses to achieve the same effect.


A potent, psychoactive alkaloid derived from peyote, a type of cactus.
Drugs that produce hallucinations.
Recreational drug—
A psychoactive drug that has no clinical value and is used to obtain a high.
Mixing of the senses, such as tasting colors or smelling sounds.

Discontinuing LSD or the other hallucinogens, especially after having used them for an extended period of time, is not easy. The residual effects of the drugs produce toxic symptoms and flashbacks, which are similar to an LSD trip.

Drugs such as LSD are often differentiated from less potent psychedelics, which have the primary effect of inducing euphoria, relaxation, stimulation, relief from pain, or relief from anxiety. This group of drugs is exemplified by marijuana, which is available worldwide. Opiates such as heroin or morphine, phencyclidine (PCP), and certain tranquilizers such as diazepam (Valium) belong to this category.

See also Hallucinations .



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MedlinePlus. “Hallucinations.” http://www.nlm.nih.gov/medlineplus/ency/article/003258.htm (accessed August 6, 2015).

National Institute on Drug Abuse. “DrugFacts: Hallucinogens—LSD, Peyote, Psilocybin, and PCP.” http://www.drugabuse.gov/publications/drugfacts/hallucinogens-lsd-peyote-psilocybin-pcp (accessed August 6, 2015).

National Institute on Drug Abuse. “What Are Hallucinogens and Dissociative Drugs?” http://www.drugabuse.gov/publications/research-reports/hallucinogensdissociative-drugs/what-are-hallucinogens (accessed August 6, 2015).


National Institute of Mental Health, 6001 Executive Blvd., Rm. 6200, MSC 9663, Bethesda, MD, 20892-9663,(866) 615-6464, nimhinfo@nih.gov, http://www.nimh.nih.gov .

National Institute on Drug Abuse, 6001 Executive Blvd., Rm. 5213, MSC 9561, Bethesda, MD, 20892-9561, (301) 443-1124, http://www.drugabuse.gov .