Hallucinogens are a broad class of drugs that induce visual and auditory hallucinations and cause profound changes in the perception of time and space, emotions, and consciousness. These drugs can be naturally occurring, such as psilocybin mushrooms, morning glory seeds, and peyote cactus (mescaline), or chemically synthesized, such as phencyclidine (commonly known as PCP or angel dust) ketamine, dizocilpine, LSD, and MDMA (commonly known as Molly or ecstasy).


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 can 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; the setting of use; whether the user is alone or with other people; and whether the substance is ingested in conjunction with other drugs or alcohol.

Hallucinogenic drugs have played a role in human life for thousands of years. Numerous indigenous cultures around the world have used hallucinogenic plants to induce states of detachment from reality, to precipitate "visions" or mystical insight, as medicines, and as adjuncts social or 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. 

LSD, also called acid, is the abbreviation of lysergic acid diethylamide, a synthetic compound and the drug most commonly identified with the term hallucinogen. It is considered the typical hallucinogen, and the characteristics of its action and effects apply to other hallucinogens. Other chemically manufactured hallucinogens include:

  • MDMA, an amphetamine, called ecstasy or Molly (for molecular)
  • 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 radical 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 on the black market in tablet, capsule, or 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 pane; 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. 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 effects 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 difficult 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. 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.

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 an extensively 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. In clinical settings, ketamine is being tested as a treatment for depression.

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 have powerful effects on the brain. The drugs induce a distorted sense of sight, hearing, and touch and change the users' impressions of time and space. On some trips, users experience sensations that are enjoyable and mentally stimulating with a sense of heightened self-awareness and mystical insight. Bad trips, however, include terrifying thoughts, nightmarish feelings of anxiety and despair that include fears of insanity, death, or losing control. Some users experience flashbacks—unsolicited repetitions of the drug experience up to one year after no further intake of the drug. People who use hallucinogen drugs may show symptoms of:

  • Difficulty concentrating, communicating or distinguishing between reality and illusion
  • Panic attacks at the height of the drug experience.
  • Distorted perceptions, impaired judgment and body-wide anesthetic with enhanced sensations, which may induce panic reactions and violent defensive behaviors
  • Agitation, paranoia
  • Perceptual distortions
  • Auditory, visual and sensory hallucinations
  • Psychosis similar to schizophrenia
  • Cardiac arrhythmias, seizures, muscle rigidity, acute renal failure, and death
  • Feelings of euphoria, mania, spirituality, and superiority to feelings of anxiousness, sadness, depression, and terror simultaneously

Physical symptoms can include:

  • Dilated pupils
  • Rapid mood and behavior fluctuations from anxious, agitated, and combative behavior to being somnolent, sedated and having a sense of relaxation and well-being
  • Mydriasis, particularly with LSD use
  • Tachycardia, tachypnea
  • Mild-to-moderate elevated heart rate and blood pressure
  • Hyperthermia, specifically during an episode of extreme exertion, combative behavior, infection
  • Degrees of cognitive distortions or deficits
  • Traumatic injuries caused by altered perceptions of reality or during combative or destructive behavior

LSD users may also show additional symptoms of:

  • Agitation and psychosis
  • Confusion and disorientation
  • Physical symptoms such as mydriasis, tachycardia and tachypnea
  • Nausea, loss of appetite and dry mouth
  • Heightened sensation
  • Trembling and tremors

In addition, two long-term symptoms associated with LSD use include persistent psychosis and hallucinogen persisting perception disorder (HPPD), more commonly known as flashbacks. The causes of these effects, which in some users occur after a single experience with the drug, are not known.


The psychosis effects of LSD are described as drug-induced psychosis—distortion or disorganization of a person's capacity to recognize reality, think rationally or communicate with others. Some LSD users experience devastating psychological effects that persist after the trip has ended, producing a long-lasting psychotic-like state. LSD-induced persistent psychosis may include dramatic mood swings from mania to profound depression, vivid visual disturbances and hallucinations. The effects may last for years and can affect people who have no history or other symptoms of psychological disorder.

Hallucinogen Persisting Perception Disorder

Some former LSD users report experiences known as flashbacks and called HPPD by physicians. These episodes are spontaneous, repeated recurrences of sensory distortions originally produced by LSD. The flashbacks can range from being pleasant to feelings of anxiety. The experience may include hallucinations, though usually the flashbacks are visual disturbances such as seeing false motion, trails attached to moving objects, or bright or colored flashes. Flashbacks generally last a minute or two. The condition is persistent and, in some cases, remains for years after the individual has stopped using the drug.

PCP and ketamine users show typical hallucinogen symptoms, and may show additional symptoms of

  • Flushing, sweating and dizziness.
  • Numbness to touch, pain or injury; hence, user may be vulnerable to potential life-threatening injuries.
  • Mixed nystagmus. Rotatory nystagmus strongly suggests PCP intoxication.
  • Confusion and poor memory.
  • Violent or self-destructive behavior.
  • Bizarre behavior that can lead to death from drownings, burns, falls (sometimes from high places), and automobile accidents.
  • Prolonged psychotic behavior and inability to speak.
  • Episodes of severe depression and schizophrenia.
  • Paranoia, fearfulness and anxiety for days.

Large doses may cause convulsions, coma, hyperthermia and death.

Chronic users report symptoms for as long as a year after he or she stops taking these drugs.

Psilocin and psilocybin (from magic mushrooms) users may experience symptoms similar to those of LSD and mescaline, and may manifest additional symptoms of

  • Hyperreflexia, anxiety and drowsiness.
  • Adverse gastrointestinal (GI) reactions associated with ingestion, including abdominal cramping, diarrhea and nausea and vomiting.

Mescaline users may have the typical hallucinogen symptoms, and may also show

  • Intoxication that generally lasts 6 to 8 hours, usually followed by somnolence
  • Adverse GI distress associated with ingestion, which includes abdominal cramping, nausea and vomiting
  • Perspiration
  • Hallucinations of all forms. but mostly intense visual images of bright colors and geometric patterns
  • Adverse perceptions of self, anxiety or depression
  • A sense of superiority and tremendous power
  • Physical injury that may have occurred because of dysphoria and sense of power, though less common than with PCP
  • Mild reflex bradycardia

Larger ingestions may produce hypotension and respiratory depression.


LSD and other hallucinogens became widely used in the the United States and Europe in the 1960s, when many young people were pursuing greater personal freedom and questioning old values and ideas. Many of these individuals used hallucinogens with a desire to expand their own consciousness and experience spiritual or psychological insight.

Hallucinogen persisting perception disorder (HPPD) occurs most commonly after LSD use. Development of the disorder is not linked to the frequency of hallucinogen use. This diagnosis is given only if the re-experiencing of perceptual disturbances causes significant distress or impairment. 


Immediate treatment during a crisis

If someone is experiencing an adverse reaction while under the influence of hallucinogens, it is important that they receive professional help as soon as possible. Quick responses can save lives. In the meantime:

  • Focus on preventing the user from harm and on keeping them safe.
  • Decrease external stimulation and agitation.
  • Calm the user. Move and speak in a reassuring and confident manner.
  • Address them by name. Remind them of who they are.
  • Tell them who you are.
  • If possible, don't leave them alone. This may mean staying with them for several hours.
  • If physical restraint is necessary, use a team approach—at least five people is best—to quickly subdue the user and minimize risks of injury to both the user and rescuers.
  • Call an ambulance. Don't delay.
  • Stay with the person until the ambulance arrives. Ask if anyone at the scene knows mouth-to-mouth resuscitation or cardiopulmonary resuscitation (CPR).
  • Ensure adequate air by keeping crowds back and opening windows. Loosen tight clothing.
  • If the person is unconscious, don't leave them on their back—they could choke. Turn them on their side and into the recovery position. Gently tilt their head back so their tongue does not block the airway.
  • If breathing has stopped, give mouth-to-mouth resuscitation. If there is no pulse, apply CPR.
  • Provide the first responders with as much information as you can: what hallucinogens were taken, when they were taken, any preexisting medical conditions known.

Drug Addiction Treatment Options

Classic hallucinogens, including LSD and psilocybin, are not considered addictive, though other hallucinogenic substances, including PCP, are. Drug addiction is a serious, though treatable disorder, requiring both physiological and psychological treatment. Success in becoming "drug free" is best achieved through formal programs that recognize abstinence, but may not be possible or realistic for everyone. The ultimate goal of all treatment programs is to enable the patient to achieve lasting abstinence; and the immediate goals are to reduce drug use, improve the patient's ability to function and minimize the medical and social complications of drug abuse.

In general, the more treatments that are given, the better the results. Many patients require other services as well, such as medical and mental-health services and HIV-prevention services. Patients who stay in treatment longer than three months usually have better outcomes than those who stay for a shorter time. Patients who go through medically assisted withdrawal to minimize discomfort but do not receive any further treatment perform about the same in terms of their drug use as those who were never treated. Over the last 25 years, studies have shown that treatment works to reduce drug intake and crimes committed by drug-dependent people. Researchers also have found that drug abusers who have been through treatment are more likely to have jobs.

Through treatment that is tailored to individual needs, patients can learn to control their condition and live normal, productive lives. Like people with diabetes or heart disease, people in treatment for drug addictions learn behavioral changes and often take medications as part of their treatment regimen.

Types of Treatment Programs

There are several types of drug abuse treatment programs. Short-term treatment programs that last less than six months include residential therapy, medication therapy, and drug-free outpatient therapy. Longer-term treatment may involve withdrawal (detoxification), pharmacotherapy and residential therapeutic community treatment. Most outpatient treatment options combine counseling and community-based support programs, and do not include medications.

Short-term residential programs, often referred to as chemical-dependency units, are often based on the "Minnesota Model" of treatment for alcoholism. These programs involve a three- to six-week inpatient treatment phase followed by extended outpatient therapy or participation in 12-step self-help groups, such as Narcotics Anonymous or Cocaine Anonymous. Chemical dependency programs for drug abuse arose in the private sector in the mid-1980s with insured alcohol-cocaine abusers as their primary patients. Today, as private provider benefits decline, more programs are extending their services to publicly funded patients. Residential programs monitor and address potential withdrawal symptoms and behavior; incorporate behavior recognition and behavioral modification therapy; and offer counseling, psychotherapy, and support groups for the person, and sometimes for their family as well. Medications help with suppressing the withdrawal syndrome and drug craving and with blocking the effects of drugs.

Longer term treatment includes Therapeutic Communities (TCs). TCs are highly structured programs in which patients stay at a residence, typically for six to 12 months. Patients in TCs include those with relatively long histories of drug dependence, involvement in serious criminal activities and seriously impaired social functioning. The focus of the TC is on resocialization of the patient to a drug-free, crime-free lifestyle.

Find a Treatment Program here.

Drug treatment programs in prisons can succeed in preventing a patient's return to criminal behavior, particularly if they are linked to community-based programs that continue treatment when the client leaves prison. Some of the more successful programs have reduced the re-arrest rate by one-fourth to one-half. For example, the "Delaware Model," an ongoing study of comprehensive treatment of drug-addicted prison inmates, shows that prison-based treatment including a therapeutic community setting, a work release therapeutic community and community-based aftercare reduces the probability of re-arrest by 57 percent and reduces the likelihood of returning to drug use by 37 percent.

Outpatient drug-free treatment does not include medications and encompasses a wide variety of programs for patients who visit a clinic at regular intervals. Most of the programs involve individual or group counseling. Patients entering these programs are abusers of drugs other than hallucinogens or are drug abusers for whom maintenance therapy is not recommended, such as those who have stable, well-integrated lives and only brief histories of drug dependence.

Drug abuse has a great economic impact on society—an estimated $67 billion per year. This figure includes costs related to crime, medical care, drug abuse treatment, social welfare programs and time lost from work. Treatment of drug abuse can reduce those costs. Studies have shown that from $4 to $7 are saved for every dollar spent on treatment. It costs approximately $3,600 per month to leave a drug abuser untreated in the community, and incarceration costs approximately $3,300 per month. In contrast, methadone maintenance therapy costs about $290 per month.

Treatment of HPPD or Flashbacks

Treatment of a hallucinogen disorder may include stress reduction and treatment of co-existing conditions such as depression or anxiety, as well as abstinence from the hallucinogen and any other substance of abuse. Small-scale studies and individual case studies have found that some symptoms of HPPD may be successfully reversed with the use of medications such naltrexone, commonly used to treat alcohol and opioid dependence; clonadine, commonly used for anxiety and hypertension; and the anti-convulsant, mood-stabilizing medication lamotrigine, commonly used to treat epilepsy and bipolar disorder.

Because HPPD symptoms may be mistaken for those of other neurological disorders such as stroke or brain tumors, sufferers may consult a variety of clinicians before the disorder is accurately diagnosed. There is no established treatment for HPPD, although some antidepressant drugs may reduce the symptoms. Psychotherapy may help patients adjust to the confusion associated with visual distraction and to minimize the fear, expressed by some, that they are suffering brain damage or psychiatric disorder.


  • National Institute on Drug Abuse
  • Drug Enforcement Administration
  • National Drug Intelligence Center

Last reviewed 02/02/2018