Hallucinogens are drugs that cause hallucinations—profound distortions in a person's perceptions of reality, including delusions and false notions. In this state, people see images, hear sounds and feel sensations that seem real but do not exist.

Hallucinogens produce rapid, intense mood swings with transitions so fast the user may feel several emotions simultaneously. Hallucinogens cause physiological symptoms such as increased heart rate and blood pressure, and may induce convulsions and seizures when used at high doses. The effects of hallucinogens are more unpredictable than those of other drugs and vary greatly from person to person. The range of effects depends on a variety of factors: the amount ingested; the user's personality, mood and expectations; if the person is alone or with others; and whether more drugs or alcohol are taken.

There is no evidence that hallucinogens increase creativity or have therapeutic value. Hallucinogens are not generally life threatening, but the user may end up killing herself while under a hallucination.

Hallucinogenic drugs have played a role in human life for thousands of years. Various cultures from the tropics to the arctic have used plants to induce states of detachment from reality, to precipitate "visions," to provide mystical insight, as medicines, and during social and religious rituals. Included in these naturally occurring substances are: mescaline from the peyote cactus plant, as well as ibogaine, psilocybin or psilocin found in certain mushrooms, known as magic mushrooms. These plants contain chemical compounds that are structurally similar to serotonin, and they produce their effects by disrupting normal functioning of the serotonin system. After the development of LSD, a synthetic compound that can be manufactured anywhere, abuse of hallucinogens became more widespread, and from the 1960s on, it increased dramatically.

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LSD is the abbreviation of the German words for lysergic acid diethylamide. It is the drug most commonly identified with the term hallucinogen and the most widely used in this class of drugs. It is considered the typical hallucinogen, and the characteristics of its action and effects apply to other hallucinogens. All LSD manufactured in this country is intended for illegal use, since LSD has no accepted medical use in the United States. Hallucinogens that are manufactured chemicals and not found in nature are:

  • LSD, also called acid
  • MDMA, an amphetamine, called ecstasy
  • PCP (phencyclidine), often called angel dust
  • Ketamine
  • DXM (dextromethorphan, found in cough medicines)

All of these agents act as neurotransmitter mimics, often as agonists or antagonists at neurotransmitter receptors. These agents cause their effects by disrupting the neurotransmission and interaction of nerve cells.


Chemist Albert Hofmann, working at the Sandoz Corporation pharmaceutical laboratory in Switzerland, first synthesized LSD in 1938. He was conducting research on possible medical applications of various lysergic acid compounds derived from ergot, a fungus that grows on rye and other grains. Searching for compounds with therapeutic value, Hofmann created more than two dozen ergot-derived synthetic molecules. The twenty-fifth was called, in German, Lyserg-Säure-Diäthylamid 25, or LSD-25. Five years after he created the drug, Hofmann accidentally ingested a small amount and experienced a series of frightening sensory effects.

LSD is the most potent of all hallucinogens. It is a clear or white, odorless, water-soluble material with a slightly bitter taste. It is initially produced in crystalline form and sold in the streets as tablets, capsules or in liquid form. Generally, the pure crystal is crushed to powder and mixed with binding agents to produce tablets known as microdots or thin squares of gelatin called window panes; or more commonly, it is dissolved, diluted and applied to paper called blotter acid, sheets of paper soaked in LSD and perforated into 1/4-inch square dosage units. Each square represents one dose. Variations in manufacturing and the presence of contaminants can produce LSD in colors ranging from clear or white, in its purest form, to tan or even black. Even uncontaminated LSD begins to degrade and discolor soon after it is manufactured. Drug distributors often apply LSD to colored paper, making it difficult for a buyer to determine the drug's purity or age.

Users of LSD typically feel some something within 30 to 90 minutes of ingestion, and the effects may last as long as 12 hours. Users refer to LSD hallucinogenic experiences as "trips" and to the negative ones as "bad trips." Most LSD trips include both pleasant and unpleasant aspects.

A person on LSD may experience physiological effects, including raised blood pressure and heart rate, dizziness, loss of appetite, dry mouth, sweating and tremors; but the drug's major effects are emotional and sensory. The user's emotions may shift rapidly from fear to euphoria, with transitions so rapid that the user may feel several things simultaneously, including panic and extreme terror. Panic and terror can lead a user to run across a busy street. LSD also has dramatic effects on the senses. Colors, smells, sounds and other sensations appear highly intensified. In some cases, a user's senses may seem to get crossed or blend in a phenomenon known as synesthesia: the feeling of hearing colors and seeing sounds. Sensation and feelings change more rapidly than the physical effects.

LSD users quickly develop a high degree of tolerance for the drug's effects: Larger doses become needed as usage increases. LSD use also produces tolerance for other hallucinogenic drugs such as psilocybin (found in magic mushrooms) and mescaline, but not to drugs such as marijuana, amphetamines and PCP, which do not act directly on the serotonin receptors affected by LSD. Tolerance for LSD is short-lived it is lost if the user stops taking the drug for several days. There is no evidence that LSD produces physical withdrawal symptoms when chronic use is stopped.

The precise mechanism by which LSD alters perceptions is still unclear. Evidence from laboratory studies suggests that LSD acts on certain groups of serotonin receptors (5-HT2 receptors) and that its effects are most prominent in two brain regions: the cerebral cortex and the locus coeruleus.

PCP, Ketamine and DXM

PCP (angel dust), Ketamine (an anesthetic), and DXM (the active ingredient in cough syrup) are commonly classified as dissociative anesthetic hallucinogens. A dissociative hallucinogen is a drug, which reduces (or blocks) signals to the conscious mind from other parts of the brain. Users report trancelike experience, as well as a feeling of being "out of body" and detached from their environment. Long-term use of dissociative anesthetics such as PCP and Ketamine (and possibly DXM) has been suspected to cause Olney's lesions.


PCP, developed in the 1950s as an intravenous surgical anesthetic, is a dissociative drug. PCP was used in veterinary medicine but is not approved for human use because of problems it causes, such as delirium, psychotic behavior and extreme agitation in patients emerging from anesthesia.

PCP is normally a white crystalline powder; sometimes it is colored with water-soluble or alcohol-soluble dyes. It is sold in powder form, tablets or capsulets. In the late 1960s, PCP in pill form became a majorly abused drug. The surge in illicit pill use rapidly receded as users became dissatisfied with the long delay between taking the drug and feeling its effects, and because of the unpredictable and often violent behavior associated with its use. In the 1970s, powdered PCP—known as ozone, rocket fuel, love boat, hog, embalming fluid, angel dust or superweed—became popular. A powdered form of the drug can be sprinkled on marijuana, tobacco or parsley, and then smoked, and the onset of effect is rapid. Users sometimes ingest PCP by snorting the powder.

PCP's effects are typically felt within minutes of ingestion and last for several hours, with some users reporting the drug's effects lasting for days. The effects of PCP are unpredictable: One drug-taking episode may produce feelings of detachment from reality, including distortions of space, time and body image; another may produce hallucinations, panic and fear. Some users report feelings of invulnerability and exaggerated strength. PCP users may become severely disoriented, violent or suicidal.

At low PCP doses (5 mg or less) physical effects include shallow, rapid breathing, elevated temperature and increased blood pressure and heart rate. Doses of 10 mg or more cause dangerous changes in blood pressure, heart rate and respiration, which are often accompanied by nausea, blurred vision, dizziness and decreased awareness of pain. Muscle contractions may cause uncoordinated movements and bizarre postures. When severe, the muscle contractions can break down muscle cells, causing bone fracture or kidney damage.

Repeated use of PCP can result in addiction, and recent research suggests that repeated or prolonged use of PCP can cause withdrawal syndrome when drug use is stopped.

When snorted or smoked, PCP rapidly passes to the brain to disrupt the functioning of sites known as NMDA (N-methyl-D-aspartate) receptor complexes, which are receptors for the neurotransmitter glutamate. Glutamate receptors play a major role in the perception of pain, in cognition—including learning and memory—and in emotion. In the brain, PCP also alters the actions of dopamine, a neurotransmitter responsible for the euphoria and "rush" associated with many abused drugs.


Ketamine ("K," "Special K," "Cat Valium," "Vitamin K") is a dissociative anesthetic developed in 1963 to replace PCP. Ketamine is currently used in human anesthesia and veterinary medicine. Much of the ketamine sold on the street has been illicitly diverted from veterinarians' offices. Although it is manufactured as an injectable liquid, in illicit use ketamine is generally evaporated to form a powder that is snorted or compressed into pills. Ketamine is odorless, tasteless and induces amnesia. Because of these properties, the drug is sometimes added to beverages of unsuspecting victims and used in the commission of sexual assaults referred to as drug rape. Ketamine is also usually ingested by large numbers of people at so-called raves.

Ketamine's chemical structure and mechanism of action are similar to those of PCP, and its effects are similar, but ketamine is much less potent than PCP, with effects of much shorter duration. Users report sensations ranging from a pleasant feeling of floating to being separated from their bodies. Some ketamine experiences involve a terrifying feeling of almost complete sensory detachment that is likened to a near-death experience. These experiences, similar to a bad trip on LSD, are called the K-hole.

DXM (dextromethorphan)

Dextromethorphan (sometimes called DXM or robo) is a cough-suppressing ingredient in a variety of over-the-counter cold and cough medications. The most common source of abused dextromethorphan is the "extra-strength" cough syrup, which typically contains 3 milligrams of the drug per milliliter of syrup. At the doses recommended for treating coughs (1/6 to 1/3 ounce of medication, containing 15 mg to 30 mg dextromethorphan), the drug is safe and effective. At much higher doses (4 or more ounces), dextromethorphan produces dissociative effects similar to those of PCP and ketamine.

The effects vary with dose, and dextromethorphan users describe a set of distinct dose-dependent "plateaus" ranging from a mild stimulant effect with distorted visual perceptions at low doses of approximately 2 ounces to a sense of complete dissociation from one's body at doses of 10 ounces or more. The effects typically last for 6 hours. Over-the-counter medications that contain dextromethorphan often contain antihistamine and decongestant ingredients as well, and high doses of these mixtures can seriously increase risks of dextromethorphan abuse.

Like PCP and ketamine, dextromethorphan acts as an NMDA receptor antagonist.

Hallucinogens. Last reviewed 12/31/1969
  • National Institute on Drug Abuse
  • Drug Enforcement Administration
  • National Drug Intelligence Center