LSD, Peyote, Psilocybin, and PCP: Part 2

How do hallucinogens affect the brain?

LSD, peyote, psilocybin, and PCP are drugs that cause hallucinations, which are profound distortions in a person's perception of reality. Under the influence of hallucinogens, people see images, hear sounds, and feel sensations that seem real but are not. Some hallucinogens also produce rapid, intense emotional swings. LSD, peyote, and psilocybin cause their effects by initially disrupting the interaction of nerve cells and the neurotransmitter serotonin.¹ Distributed throughout the brain and spinal cord, the serotonin system is involved in the control of behavioral, perceptual, and regulatory systems, including mood, hunger, body temperature, sexual behavior, muscle control, and sensory perception. On the other hand, PCP acts mainly through a type of glutamate receptor in the brain that is important for the perception of pain, responses to the environment, and learning and memory. There have been no properly controlled research studies on the specific effects of these drugs on the human brain, but smaller studies and several case reports have been published documenting some of the effects associated with the use of hallucinogens.

• LSD: Sensations and feelings change much more dramatically than the physical signs in people under the influence of LSD. The user may feel several different emotions at once or swing rapidly from one emotion to another. If taken in large enough doses, the drug produces delusions and visual hallucinations. The user's sense of time and self is altered. Experiences may seem to "cross over" different senses, giving the user the feeling of hearing colors and seeing sounds. These changes can be frightening and can cause panic. Some LSD users experience severe, terrifying thoughts and feelings of despair, fear of losing control, or fear of insanity and death while using LSD.
  
  LSD users can also experience flashbacks, or recurrences of certain aspects of the drug experience. Flashbacks occur suddenly, often without warning, and may do so within a few days or more than a year after LSD use. In some individuals, the flashbacks can persist and cause significant distress or impairment in social or occupational functioning, a condition known as hallucinogen-induced persisting perceptual disorder (HPPD).
  
  Most users of LSD voluntarily decrease or stop its use over time. LSD is not considered an addictive drug, since it does not produce compulsive drug-seeking behavior. However, LSD does produce tolerance, so some users who take the drug repeatedly must take progressively higher doses to achieve the state of intoxication that they had previously achieved. This is an extremely dangerous practice, given the unpredictability of the drug. In addition, cross-tolerance between LSD and other hallucinogens has been reported.
• Peyote: The long term residual psychological and cognitive effects of mescaline, peyote's principal active ingredient, remain poorly understood. A recent study found no evidence of psychological or cognitive deficits among Native Americans who use peyote regularly in a religious setting.² It should be mentioned, however, that these findings may not generalize to those who repeatedly abuse the drug for recreational purposes. Peyote abusers may also experience flashbacks.
• Psilocybin: The active compounds in psilocybin-containing "magic" mushrooms have LSD-like properties and produce alterations of autonomic function, motor reflexes, behavior, and perception.³ The psychological consequences of psilocybin use include hallucinations, an altered perception of time, and an inability to discern fantasy from reality. Panic reactions and psychosis may also occur, particularly if a user ingests a large dose. Long term effects such as flashbacks, risk of psychiatric illness, impaired memory, and tolerance have been described in case reports.
• PCP: The use of PCP as an approved anesthetic in humans was discontinued in 1965 because patients often became agitated, delusional, and irrational while recovering from its anesthetic effects. PCP is a "dissociative drug," meaning that it distorts perceptions of sight and sound, and produces feelings of detachment from the environment and self. First introduced as a street drug in the 1960s, PCP quickly gained a reputation as a drug that could cause bad reactions and was not worth the risk. However, some abusers continue to use PCP due to the feelings of strength, power, and invulnerability, as well as a numbing effect on the mind, that PCP can induce. Among the adverse psychological effects reported are
  • Symptoms that mimic schizophrenia: Delusions, hallucinations, paranoia, disordered thinking, and a sensation of distance from one's environment.
  • Mood disturbances: Approximately 50% of individuals brought to emergency rooms because of PCP-induced problems—related to use within 48 hours—report significant elevations in anxiety symptoms.⁴
  • Long term effects: People who have abused PCP for long periods of time have reported memory loss, difficulties with speech and thinking, depression, and weight loss. These symptoms can persist up to one year after stopping PCP abuse.
  • Addiction: PCP is addictive; its repeated abuse can lead to craving and compulsive PCP-seeking behavior, despite severe adverse consequences.

References

1. Fantegrossi, W. E., Murnane, K. S., & Reissig, C. J. (2008). The behavioral pharmacology of hallucinogens. Biochemical Pharmacology, 75, 17-33.
2. Halpern, J. H., Sherwood, A. R., Hudson, J. I., Yurgelun-Todd, D., & Pope, H. G. Jr. (2005). Psychological and cognitive effects of long term peyote use among Native Americans. Biological Psychiatry, 58, 624-631.
3. Cunningham, N. (2008). Hallucinogenic plants of abuse. Emergency Medicine Australasia, 20, 167-174.
4. Yago, K. B., Pitts, F. N., Burgoyne, R. W., Aniline, O., Yago, L. S., & Pitts, A. F. (1981). The urban epidemic of phencyclidine (PCP) use: Clinical and laboratory evidence from a public psychiatric hospital emergency service. Journal of Clinical Psychiatry, 42, 193-196.