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Hallucinogens are a broad class of drugs that induce visual and auditory hallucinations, or profound distortions in a person's perceptions of reality. These drugs can be naturally occurring, such as psilocybin mushrooms, morning glory seeds, and peyote cactus (mescaline); they may also be chemically synthesized, such as phencyclidine (commonly known as PCP or angel dust), ketamine, dizocilpine, lysergic acid diethylamide (LSD), and 3,4-Methylenedioxymethamphetamine or MDMA (commonly known as Molly or ecstasy).

Hallucinogens may cause profound changes in the perception of time, space, or consciousness. In some cases, the hallucinations caused by this class of drug are purely visual or sensory; in other cases, they include delusions and false notions. Certain kinds of hallucinogens can also produce rapid, intense mood swings. Some report that these transitions occur so quickly that users feel as if they are experiencing several emotions simultaneously. Hallucinogens can also cause physiological symptoms such as increased heart rate and blood pressure and may induce convulsions and seizures when used at high doses. Some hallucinogens, like PCP, have been known to cause death when taken in high doses, though many PCP-related deaths are a result of its behavioral effects.

Hallucinogenic drugs—particularly naturally occurring substances such as mescaline, ibogaine, or magic mushrooms—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, or as adjuncts to social and religious rituals.

LSD and other manufactured hallucinogens were first synthesized in early- to mid-20th century. They first became widely used in the United States and Europe in the 1960s. Many of the individuals who used hallucinogens expressed a desire to expand their own consciousness and experience spiritual or psychological insight.


    Hallucinogens have powerful effects on the brain. The drugs can induce a distorted sense of sight, hearing, and touch, or 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 insight. "Bad trips," however, can include terrifying thoughts and nightmarish feelings of anxiety, paranoia, and despair; these may include fears of insanity, death, or losing control of one’s mind or body.

    According to the National Institute on Drug Abuse, people who use hallucinogenic drugs may experience:

    • Difficulty concentrating, communicating clearly, or distinguishing between reality and illusion
    • Panic attacks, often at the height of the drug experience
    • Distorted perceptions, impaired judgment, and body-wide dissociative or stimulating sensations, which may induce panic reactions or violent defensive behaviors
    • Agitation or paranoia
    • Perceptual distortions
    • Feelings of euphoria, mania, spirituality, and superiority
    • Feelings of anxiousness, sadness, depression, and terror

    Physical symptoms can include:

    • Mydriasis (dilated pupils), particularly with LSD use
    • Rapid behavior fluctuations from agitated and combative behavior to appearing somnolent, sedated, or relaxed
    • Tachycardia (rapid heart rate) or tachypnea (rapid breathing)
    • Mild to moderate elevations in blood pressure
    • Hyperthermia, or increased body temperature, specifically during an episode of extreme exertion, combative behavior, or infection
    • In some cases, traumatic injuries caused by altered perceptions of reality or during combative or destructive behavior
    • Cardiac arrhythmias, seizures, muscle rigidity, acute renal failure, and in some cases, death

    LSD users may also show symptoms of:

    • Agitation and psychosis (disconnection from reality)
    • Confusion and disorientation
    • Physical symptoms such as mydriasis, tachycardia, and tachypnea
    • Nausea, loss of appetite, and dry mouth
    • Heightened sensations
    • Trembling and tremors

    Two long-term symptoms associated specifically with LSD use include:

    • Persistent psychosis
    • Hallucinogen persisting perception disorder (HPPD), more commonly known as flashbacks

    Persistent Psychosis

    Some LSD users experience devastating psychological effects that persist after the trip has ended, producing a long-lasting psychotic-like state. This may limit their capacity to recognize reality, think rationally, or communicate with others. LSD-induced persistent psychosis may include dramatic mood swings from mania to profound depression, vivid visual disturbances, and hallucinations. In rare cases, the effects may last for years. Though some literature reviews indicate that these symptoms may be more likely to occur in those with a family history of schizophrenia, they have also been known to occur in people who have no history or other symptoms of psychological disorder.

    Hallucinogen Persisting Perception Disorder

    Some former LSD users report experiences popularly known as flashbacks; this phenomenon is called Hallucinogen Persisting Perception Disorder, or HPPD, by physicians. These episodes are spontaneous, repeated recurrences of the sensory distortions that were originally produced by LSD. The flashbacks can range from being pleasant to triggering 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 can be 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, including:

    • Flushing, sweating, and dizziness
    • Numbness to touch, pain, or injury; as a result, the user may be vulnerable to potential injuries, some life-threatening
    • Mixed nystagmus, or repetitive, uncontrolled movements of the eyes
    • Confusion, 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-related symptoms
    • Paranoia, fearfulness, or anxiety, sometimes lasting for several days afterward
    • Prolonged, repeated use of ketamine is associated with a condition known as “ketamine bladder syndrome,” a persistent form of bladder damage that presents with symptoms similar to a urinary tract infection

    Large doses—particularly of PCP—may cause convulsions, coma, hyperthermia, and death. Chronic users may 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 (overreactive reflexes), which may trigger feelings of anxiety
    • Drowsiness
    • Adverse gastrointestinal reactions associated with ingestion, including abdominal cramping, diarrhea, nausea, and vomiting

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

    • Intoxication generally lasts six to eight hours, usually followed by somnolence
    • Adverse gastrointestinal distress associated with ingestion, including abdominal cramping, nausea, or vomiting
    • Perspiration
    • Hallucinations, typically include intense visual images of bright colors and geometric patterns
    • Adverse perceptions of self, which may trigger anxiety or depression
    • A sense of superiority and tremendous power
    • Physical injury that may have occurred because of dysphoria and sense of power
    • Slow heart rate
    • Larger ingestions may produce hypotension, low blood pressure, or respiratory depression

    The effects of hallucinogens may result in part from their interference with the activity of brain chemicals such as serotonin and glutamate, according to the National Institute on Drug Abuse.

    What are some chemically manufactured hallucinogens?

    • DXM, or dextromethorphan; most commonly found in cough medicine

    • Ketamine

    • LSD, or lysergic acid diethylamide; also called acid

    • MDMA, an amphetamine; also called ecstasy or Molly

    • PCP, or phencyclidine; often called angel dust

    Why do people react differently to hallucinogens?

    The effects of hallucinogens are typically more unpredictable than those of other drugs because the class contains several different compounds, each of which has effects that can vary greatly from person to person. The range of effects depends on a variety of factors: the amount ingested; physiological factors such as the user’s weight and metabolism; the user's personality, mood, history of mental illness, and expectations; the setting of use; whether the user is alone or with other people; and whether the substance is ingested alone or in conjunction with other drugs or alcohol.

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    Immediate Treatment During a Crisis

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

    • 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 manner
    • Address them by name
    • If possible, remain with them; this may mean staying with them for several hours
    • Call an ambulance and stay with the person until the ambulance arrives
    • Ensure adequate air by keeping crowds back and opening windows
    • If the person is unconscious, turn them on their side and 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 possible, including what hallucinogens were taken, when they were taken, and any preexisting medical conditions, if known

    Drug Addiction Treatment Options

    Most “classic” hallucinogens, including LSD and psilocybin, are not considered addictive; other hallucinogenic substances, including PCP, are. Drug addiction is a serious disorder that requires both physiological and psychological treatment.

    As with chronic physical conditions like diabetes, with adequate treatment, those struggling with addiction can learn to control their condition and live normal, productive lives. Treatment for drug addiction should incorporate behavioral changes to help patients manage cravings and triggers; patients may also take medications as part of their treatment regimen.

    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.

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    Treatment of Hallucinogen Persisting Perception Disorder (HPPD)

    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. There is no clinically established treatment for HPPD, although some drugs may be prescribed off-label to reduce the symptoms. Small-scale studies and individual case studies have found that some symptoms of HPPD may be successfully reversed with the use of medications such as naltrexone, commonly used to treat alcohol and opioid dependence; clonidine, commonly used for anxiety and hypertension; and the anti-convulsant, mood-stabilizing medication lamotrigine, commonly used to treat epilepsy and bipolar disorder.

    Can hallucinogen persisting perception disorder be confused with other neurological disorders?

    Hallucinogen persisting perception disorder symptoms may be mistaken for those of other neurological disorders such as stroke or brain tumors, sufferers often consult multiple clinicians before the disorder is accurately diagnosed.

    National Institute on Drug Abuse
    Drug Enforcement Administration
    National Institute of Mental Health
    Last updated: 12/03/2021