What Are the Effects of Hallucinogens?

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Question: What Are the Effects of Hallucinogens?

Answer: Researchers believe that hallucinogens alter the perceptions of users by acting on neural circuits in the brain, particularly in 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 National Institute on Drug Abuse (NIDA) research.

What are the 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 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 a 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, provided by the NIDA:


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

Short-Term General Effects of Hallucinogens

Sensory Effects

  • 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)
  • Changes in sense or perception of time (time goes by slowly)

Physical Effects

  • Increased energy and heart rate
  • Nausea

What are the Long-Term Effects of Hallucinogens?

One result of 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.

This tolerance 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 the 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.

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

According to the NIDA, here are some of the specific long-term effects of hallucinogen use:

Long-Term Effects

Persistent Psychosis

  • Visual disturbances
  • Disorganized thinking
  • Paranoia
  • Mood disturbances

Hallucinogen Persisting Perception Disorder (Flashbacks)

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

Back to: Hallucinogens FAQ


National Institute on Drug Abuse. "Hallucinogens and Dissociative Drugs." Research Report Series Updated January 2014

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