Hallucinogen Effects in the Short- and Long-Term

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Researchers believe that hallucinogens alter the perceptions of users by acting on neural circuits in the brain, particularly in the prefrontal cortex, a region of the brain involved in perception, mood, and cognition. Whereas dissociative drugs are thought to disrupt glutamate transmitters in the brain, hallucinogens are believed to affect the neurotransmitter serotonin.

Hallucinogens can also affect regions of the brain that deal with regulating arousal and physiological responses to stress and panic, according to the National Institute on Drug Abuse (NIDA) research.

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Short-Term Effects of Hallucinogens

People who use hallucinogens can see things, hear things and feel sensations that seem to be very real, but do not in fact exist. These altered perceptions are known as hallucinations. Typically, these hallucinatory effects can begin from 20 to 90 minutes after ingestion and can last up to 12 hours.

One problem for users of hallucinogens is the fact that the effects of the drug can be highly unpredictable. The amount ingested, plus the user's personality, mood, surroundings, and expectations can all play a role in how the "trip" will go.

What hallucinogens can do is distort the user's capacity to recognize reality, think rationally and communicate. In short, a drug-induced psychosis, and an unpredictable one.

Sometimes, the user will experience an enjoyable and mentally stimulating trip. Some report having a sense of heightened understanding. But, users can have a "bad trip," that produces terrifying thoughts and feelings of anxiety and despair.

According to NIDA research, bad trips can result in fears of losing control, insanity, or death.

The following is a list of short-term effects of hallucinogenic drugs (i.e. poppers), provided by the NIDA:

  • Dizziness and sleeplessness
  • Impulsiveness and rapid emotional shifts that can range from fear to euphoria, with transitions so rapid that the user may seem to experience several emotions simultaneously
  • Increased blood pressure, heart rate, and body temperature
  • Loss of appetite, dry mouth, and sweating
  • Numbness, weakness, and tremors


Psilocybin is a naturally occurring hallucinogen found in some types of mushrooms. It can cause:

  • Feelings of relaxation (similar to the effects of low doses of marijuana)
  • Nervousness, paranoia, and panic reactions
  • Introspective/spiritual experiences

General Effects of Hallucinogenic Drugs

While the effects can vary depending on the type of hallucinogen and dosage, there are some general short-term effects that most of these drugs share.

Sensory Effects

  • Changes in sense or perception of time (time goes by slowly)
  • Hallucinations, including seeing, hearing, touching, or smelling things in a distorted way or perceiving things that do not exist
  • Intensified feelings and sensory experiences (brighter colors, sharper sounds)
  • Mixed senses (“seeing” sounds or “hearing” colors)

Physical Effects

  • Increased energy and heart rate
  • Nausea

Long-Term Effects of Halluconigens

One result of the repeated use of hallucinogens is the development of tolerance. Studies show that LSD users develop a high degree of tolerance for the drug very quickly. This means they have to take increasingly larger amounts to get the same effects.

Research indicates that if a user develops a tolerance to one drug in the hallucinogen class, he or she will also have a tolerance for other drugs in the same class. For example, if someone has developed a tolerance to LSD, they will also have a tolerance to psilocybin and mescaline.

They will not, however, have a tolerance to drugs that affect other neurotransmitter systems, such as amphetamines and marijuana.

Tolerance to hallucinogens is not permanent. If the person stops taking the drug for several days, the tolerance will disappear.

Also, chronic users of hallucinogens typically do not experience any ​physical withdrawal symptoms when they cease use of drugs, unlike users who have become dependent on other drugs or alcohol.

Persistent Psychosis and Flashbacks

Two of the more serious long-term effects of hallucinogen use are persistent psychosis and flashbacks, otherwise known as hallucinogen persisting perception disorder (HPPD). Many times these conditions will occur together. According to the NIDA, here are some of the specific long-term effects of hallucinogen use:

Persistent Psychosis

  • Disorganized thinking
  • Mood disturbances
  • Paranoia
  • Visual disturbances

Hallucinogen Persisting Perception Disorder

  • Hallucinations
  • Other visual disturbances (such as seeing halos or trails attached to moving objects)
  • Symptoms sometimes are mistaken for neurological disorders (such as stroke or brain tumor)

Although rare, the occurrence of these conditions is as unpredictable as having a bad trip.

Flashbacks and psychosis can happen to anyone, but research has shown that they are more often observed in patients with a history of psychological problems.

The NIDA reports that persistent psychosis and flashbacks can occur to some users even after a single exposure to hallucinogenic drugs. There is really no established treatment for flashbacks, although many who experience them are treated with antidepressants, antipsychotic drugs, and psychotherapy.

6 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Buddy T
Buddy T is an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism.