En español
NIDA

Menu

Hallucinogens and Dissociative Drugs

How Do Hallucinogens (LSD and Psilocybin) Affect the Brain and Body?

photo of Hallucinogens

How Do Hallucinogens Work?

Classic hallucinogens are thought to produce their perception-altering effects by acting on neural circuits in the brain that use the neurotransmitter serotonin.6-9 Specifically, some of their most prominent effects occur in the prefrontal cortex—an area involved in mood, cognition, and perception—as well as other regions important in regulating arousal and physiological responses to stress and panic.

What are the Short-Term Effects of Hallucinogens?

Ingesting hallucinogenic drugs can cause users to see images, hear sounds, and feel sensations that seem real but do not exist.

Ingesting hallucinogenic drugs can cause users to see images, hear sounds, and feel sensations that seem real but do not exist. Their effects typically begin within 20 to 90 minutes of ingestion and can last as long as 12 hours. Experiences are often unpredictable and may vary with the amount ingested and the user’s personality, mood, expectations, and surroundings. The effects of hallucinogens like LSD can be described as drug-induced psychosis—distortion or disorganization of a person’s capacity to recognize reality, think rationally, or communicate with others. Users refer to LSD and other hallucinogenic experiences as “trips” and to acute adverse or unpleasant experiences as “bad trips.” On some trips, users experience sensations that are enjoyable and mentally stimulating and that produce a sense of heightened understanding. Bad trips, however, include terrifying thoughts and nightmarish feelings of anxiety and despair that include fears of losing control, insanity, or death. Specific short-term effects of LSD and psilocybin include:

LSD

  • Increased blood pressure, heart rate, and body temperature
  • Dizziness and sleeplessness
  • Loss of appetite, dry mouth, and sweating
  • Numbness, weakness, and tremors
  • 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

Psilocybin

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

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?

LSD users quickly develop a high degree of tolerance to the drug’s effects, such that repeated use requires increasingly larger doses to produce similar effects. Use of hallucinogenic drugs also produces tolerance to other drugs in this class, including psilocybin and mescaline. Use of classic hallucinogens does not, however, produce tolerance to drugs that do not act directly on the same brain cell receptors (in other words, there is no cross-tolerance to drugs that act on other neurotransmitter systems, such as marijuana, amphetamines, or PCP, among others). Furthermore, tolerance for hallucinogenic drugs is short-lived—it is lost if the user stops taking the drugs for several days—and physical withdrawal symptoms are typically not experienced by users when chronic use is stopped.

LSD users quickly develop a high degree of tolerance to the drug’s effects, such that repeated use requires increasingly larger doses to produce similar effects.

Two long-term effects—persistent psychosis and hallucinogen persisting perception disorder (HPPD; also often referred to as “flashbacks”)—have been associated with use of classic hallucinogens (see below). Although occurrence of either is rare, it is also unpredictable and may happen more often than previously thought, and sometimes both conditions occur together. While the exact causes are not known, both conditions are more often seen in individuals with a history of psychological problems but can happen to anyone, even after a single exposure. There is no established treatment for HPPD, in which flashbacks may occur spontaneously and repeatedly although less intensely than their initial occurrence. Some antidepressant and antipsychotic drugs can be prescribed to help improve mood and treat psychoses, however. Psychotherapy may also help patients cope with fear or confusion associated with visual disturbances or other consequences of long-term LSD use. More research on the causes, incidence, and long-term effects of both disorders is being conducted.

Long-Term Effects of Hallucinogens

Blurry photo of male

Persistent psychosis

  • Visual disturbances
  • Disorganized thinking
  • Paranoia
  • Mood disturbances

Hallucinogen Persisting Perception Disorder (HPPD)

  • 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)

† Misidentification of poisonous mushrooms resembling psilocybin could lead to unintentional, potentially fatal poisoning.

‡ Mescaline is not described in this report.

This page was last updated January 2014

​Research Reports

This series of reports simplifies the science of research findings for the educated lay public, legislators, educational groups, and practitioners. The series reports on research findings of national interest.

Featured Publication

Featured Publication

Drugs, Brains, and Behavior - The Science of Addiction

As a result of scientific research, we know that addiction is a disease that affects both brain and behavior.

Ordering Publications

Call 1-877-643-2644 or:

NIDA Drug Pubs