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Hallucinogens hə-ˈlüs-ᵊn-ə-jən

By Patrick G. O’Connor, MD, MPH, Professor of Medicine; Chief, Section of General Internal Medicine, Yale University School of Medicine

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  • Hallucinogens distort and intensify sensations, but the actual effects can depend on the user’s mood and expectations.

  • The chief dangers are the psychologic effects and impaired judgment they cause.

  • A dark, quiet room and calm, nonthreatening talk can help users who are experiencing a bad trip.

Hallucinogens include LSD (lysergic acid diethylamide), psilocybin (mushroom), mescaline (peyote), dimethyltryptamine (DMT), and 2,5-dimethoxy-4-methylamphetamine (DOM or STP), an amphetamine derivative. Many new compounds are being synthesized, and the list of hallucinogens is growing.

These drugs may be taken various ways. LSD is taken by mouth using tablets or blotter paper. DMT can be smoked.

People may become psychologically dependent on hallucinogens, but physical dependence, which results in unpleasant symptoms (withdrawal) when the drug is stopped, is not typical.


Hallucinogens distort and intensify auditory and visual sensations. For example, people may feel as if they are seeing sounds and hearing colors. People feel as if they are not real (called depersonalization) or are detached from their environment (called dissociation). Many hallucinogens cause nausea and vomiting. LSD causes blurred vision, sweating, palpitations, and impaired coordination.

The actual effect can depend on the user’s mood and expectations when the drug is taken and the setting in which the drug is taken. For example, users who were depressed before the drug was taken are likely to feel sadder when the drug takes effect. The chief dangers of using these drugs are the psychologic effects and impaired judgment they cause, which can lead to dangerous decisions or accidents. For example, users may think they can fly and may even jump out a window to prove it.

The user’s ability to cope with the visual and auditory distortions also affects the experience—or “trip.” Inexperienced, frightened users are less able to cope than someone who is more experienced and not afraid of the trip. Users under the influence of a hallucinogen, usually LSD, can become extremely anxious and begin to panic, resulting in a bad trip. They may want to stop the trip, which is not possible.

Some users remain out of touch with reality (psychotic) for many days or longer after the drug’s effects have worn off. A prolonged psychosis is more likely in users with a preexisting mental health disorder.

Some people—especially long-term or repeated users of hallucinogens, particularly LSD—may experience flashbacks after they stop using the drugs. Flashbacks are similar to but generally less intense than the original experience. Typically, flashbacks disappear over 6 to 12 months but can recur as long as 5 years after the last use of LSD, especially in users who still have an anxiety or another mental health disorder.

Diagnosis and Treatment

Doctors usually base the diagnosis on symptoms. Tests are not available to confirm the use of many of these drugs.

Most users do not seek treatment. A quiet, dark room and calm, nonthreatening talk can help users who are having a bad trip. They need reassurance that the effects are caused by the drug and will end. If anxiety is severe, benzodiazepines (sedatives), such as lorazepam, may help. People who experience a prolonged psychosis may need mental health treatment.

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