En español

Hallucinogens and Dissociative Drugs

How Do Hallucinogens (LSD, Psilocybin, Peyote, DMT, and Ayahuasca) Affect the Brain and Body?

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 (Passie, 2008; Nichols, 2004; Schindler, 2012; Lee, 2012). 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. 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.

Like LSD and psilocybin, DMT produces its effects through action at serotonin (5-HT) receptors in the brain (Strassman, 1996). Some research has suggested that DMT occurs naturally in the human brain in small quantities, leading to the hypothesis that release of endogenous DMT may be involved in reports of alien abductions, spontaneous mystical experiences, and near-death experiences, but this remains controversial (Barker, 2012).

Specific short-term effects of LSD, psilocybin, peyote, DMT, and ayahuasca include:


  • 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


  • Feelings of relaxation (similar to effects of low doses of marijuana)
  • Nervousness, paranoia, and panic reactions
  • Introspective/spiritual experiences
  • Misidentification of poisonous mushrooms resembling psilocybin could lead to unintentional, potentially fatal poisoning


  • Increased body temperature and heart rate
  • Uncoordinated movements (ataxia)
  • Profound sweating
  • Flushing


  • Increased heart rate
  • Agitation
  • Hallucinations frequently involving radically altered environments as well as body and spatial distortions


  • Increased blood pressure
  • Severe vomiting (induced by the tea)
  • Profoundly altered state of awareness and perceptions of otherworldly imagery

Short-Term General Effects of Hallucinogens

A woman having intensified sensory experiences depicted by swirling colors

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 peyote. 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 not typically experienced when chronic use is stopped.

The long-term residual psychological and cognitive effects of peyote remain poorly understood. Although one study found no evidence of psychological or cognitive deficits among Native Americans who use peyote regularly in a religious setting, those findings may not generalize to those who repeatedly abuse the drug for recreational purposes (Halpern, 2005). Peyote users may also experience hallucinogen persisting perception disorder (HPPD)—also often referred to as flashbacks. The active ingredient mescaline has also been associated, in at least one report, to fetal abnormalities (Gilmore, 2001).

Long-term effects of DMT use and abuse and addiction liability are currently unknown. Unlike most other hallucinogens, DMT does not appear to induce tolerance (Winstock, 2013).

As with some other hallucinogens, there is little information to suggest that ayahuasca use creates lasting physiological or neurological deficits, especially among those using the brew for religious activities.

Overall, two long-term effects—persistent psychosis and HPPD—have been associated with use of classic hallucinogens (see text box 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 a male to depict psychosis

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)

This page was last updated February 2015

Get this Publication

NIDA Notes: The Latest in Drug Abuse Research

​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.