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What Are Hallucinogens?

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Hallucinogens are drugs that alter the user’s thinking processes and perception in a manner that leads to significant distortions of reality 1. These drugs affect one’s perception far differently than many other types of drugs do. To many, the influence of these drugs represents experiences of new and even expanded consciousness and, indeed, some individuals experience synesthesia (mixed sensory experiences, such as seeing sounds or hearing colors). Other common effects produced by these drugs include hallucinations, an altered sense of time, and dissociative experiences (e.g., not feeling connected to one’s body or reality).

Most hallucinogens are classified by the United States Drug Enforcement Administration (DEA) as Schedule I controlled substances, meaning they have no known medicinal uses and have a high potential for abuse and physical or psychological dependence 2. Hundreds of compounds are classified as hallucinogens.

Some of the more common hallucinogens include:

Ketamine is a Schedule III drug and PCP is a Schedule II, due to their previous medical uses, but they are serious drugs of concern nonetheless 2.

While these are not typically major drugs of abuse, in 2014 an estimated 1.2 million individuals over the age of 12 reported using hallucinogens 3. They have been used for a variety of purposes, including religious, stress-relief, recreational, or to reach enlightenment or understanding. These drugs, although not considered to be classically addictive, can lead to severe consequences and impairments.

Types of Hallucinogens

Hallucinogens can be classified into two subcategories: the classic hallucinogens and the dissociative drugs. Classic hallucinogens typically produce visual and auditory hallucinations and may result in an altered sense of time and heightened sensory experiences. Dissociative drugs produce feelings of detachment, such as derealization (the feeling that one is detached from reality or that things are not real) and depersonalization (the feeling that one is detached from one’s own physical body) 4,5.

The classic hallucinogens discussed in this article include:

  • LSD.
  • Psilocybin.
  • Peyote.
  • DMT.

The dissociative drugs discussed in this article include:

  • PCP
  • Ketamine.


LSD (lysergic acid diethylamide) is a synthetic drug that in small amounts can produce very powerful visual hallucinations and mood alterations 6. LSD was developed in 1938 by chemist Albert Hofmann, who was conducting research with ergot, a fungus, to develop its potential as a circulatory stimulant 7. The fungus had no practical uses for this purpose and it was shelved. Five years later, Hoffman began working with it again and, after accidentally absorbing it through his fingertips, he experienced the drug’s hallucinogenic effects. After experimenting with his colleagues, the drug was marketed as a potential benefit to patients in psychotherapy 7,8.

Most individuals using LSD typically feel euphoric, experience visual hallucinations, and often have very intense moods; however, so-called “bad trips” can occur in individuals, resulting in extreme anxiety (including panic attacks) and significant depression.6,7.

LSD is typically taken as a capsule , liquid, or “blotter paper” that has been dosed with LSD liquid 6. It’s commonly referred to as acid, dots, blotter acid, window pane, and mellow yellow 6. Though a standard dose averages in the mere micro-milligram range, the effects can last up to 12 hours 7,9. LSD was a very popular drug in the 1960s and early 1970s, and its use was partly responsible for the drug culture of that time. LSD faded in popularity over the years, but it may be making a mild comeback. In 2013, 229,000 individuals over the age of 12 admitted to current usage of LSD 10.

LSD use does not appear to result in physical dependence, although tolerance can develop 5. Other potential effects of LSD include 9:

man taking lsd
  • Increased body temperature, heart rate, and blood pressure.
  • Profound sweating.
  • Dizziness.
  • Loss of appetite.
  • Dry mouth.
  • Tremors.
  • Numbness.
  • Impulsiveness.
  • Mood swings.
  • Hallucinations.
  • Distorted thinking.

Long-term LSD use, in rare cases, can lead to Hallucinogen Persisting Perception Disorder, or chronic flashbacks of experiences while on LSD 5. These flashbacks can cause significant impairment or distress in the user’s life and can last for years 5.


Psilocybin (4-phosphoryloxy-N,N-dimethyltryptamine) is a hallucinogenic substance that is found in more than 200 types of mushrooms 11,12. These mushrooms are typically found in certain regions of South America, Mexico, and the United States 12. Common street names for mushrooms that contain psilocybin include magic mushrooms, mushrooms, and shrooms 12. The mushrooms are typically eaten, and they are also commonly brewed as a tea 12.

A few effects of eating mushrooms include 9, 12:

  • Relaxation.
  • Spiritual experiences.
  • Hallucinations.
  • Panic.
  • Paranoia.
  • Psychosis.
  • Nausea.
  • Vomiting.

One risk associated with psilocybin use is that of poisoning. Users may misidentify the mushrooms and accidentally ingest poisonous mushrooms, which can result in death 9, 12.

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Peyote is a small cactus containing the active ingredient, mescaline 13. Mescaline comes from the small protrusions (“buttons”) on the cactus but can also be produced artificially 13. Peyote may be one of the oldest known hallucinogenic drugs. It was used in Mexico by the Aztecs and by certain groups of Native Americans. These groups used it for hallucinogenic and medicinal purposes. Some Native American churches still have the legal right to use peyote in religious services despite its classification by the DEA 14. Others have used mescaline, as well as other hallucinogens, to enhance creativity and promote appreciation of beauty and art 14.

Typically, the peyote cactus buttons are eaten or soaked in water 13. They can also be ground and put in a capsule or smoked with tobacco or marijuana 13. Users tend to experience the psychoactive effects of mescaline within one to two hours after ingestion, and its effects can last up to 12 hours 9. These effects include 9,13:

  • Increased heart rate and body temperature.
  • Vomiting.
  • Flushed skin.
  • Extreme sweating.
  • Coordination problems.
  • Hallucinations.
  • Altered perception and body image.
  • Anxiety.

It’s not likely that individuals using peyote or mescaline will become addicted, but tolerance, as well as cross-tolerance to other hallucinogens, can develop 9. Regular use does not appear to result in the development of physical dependence and withdrawal symptoms are uncommon 9.


What is Ayahuasca? 

Ayahuasca is a hallucinogenic tea that is usually brewed with a DMT-containing plant. It’s primarily used in South America for religious or healing purposes 15.

DMT (N,N-Dimethyltryptamine) , or “Dimitri,” is a hallucinogenic chemical that occurs naturally in some Amazonian plants, but can also be artificially synthesized. When made in a laboratory, DMT looks like a white, crystalline powder and is most often smoked. The worldwide use of DMT is increasing, as it has a large number of new users compared to other drugs 16.

Small amounts of DMT may occur naturally in the human brain. These trace quantities of DMT are hypothesized to be involved in people’s reports of certain unusual events, such as near-death encounters, mystical experiences, or alien abductions 15.

Unlike many other hallucinogens with relatively long duration of effects, DMT produces an intense but short-lived intoxication 16. Overall, users have not reported many negative adverse or “comedown” effects 15.

The effects of DMT may include 9:

  • Hallucinations.
  • Body and spatial distortions.
  • Changes in awareness and perception.
  • Increased heart rate and blood pressure.
  • Agitation.
  • Severe vomiting (due to ayahuasca tea).

Long-term DMT use doesn’t appear to cause tolerance and there is little evidence surrounding the long-term effects of ayahuasca use. The tea doesn’t appear to cause any lasting physical or mental health problems 15.


Phencyclidine (PCP) was initially developed as a general anesthetic, but because its use is associated with serious side effects, the dissociative drug is no longer used medicinally. It’s still legal for use in animals but is rarely used in veterinary settings. Pure PCP is white and crystalline in appearance but additives may give it a tan or brown color 17. PCP is commonly taken orally in tablet or capsule form, smoked, snorted as a powder, or injected 17. Street names for PCP include angel dust, animal tranquilizer, and rocket fuel 17. At least 14 types of PCP were sold on the street between the late 1960s and 1990s 18 and many illegal samples contain PCC, a toxic chemical which releases cyanide and can cause poisoning 17.

Although the prevalence of PCP addiction or PCP use disorder is unknown, about 2.5% of the population has reported using PCP at least once in their lives 5.

The effects of PCP vary depending on the dose, but in general, the user will feel effects within 1-5 minutes if the hallucinogen is injected or smoked and within about 30 minutes if taken orally or snorted 17. Intoxication typically lasts about 4-6 hours, and effects may include 5, 17:

vial of pcp
  • Euphoria.
  • Feelings of invulnerability and strength.
  • Disorientation.
  • Distorted sensory perception.
  • Disordered thoughts.
  • Hallucinations and illusions.
  • Violent or bizarre behaviors.
  • Severe anxiety.
  • Amnesia.
  • Paranoia.
  • Numbness or diminished response to pain.
  • Seizures.

The effects of the drug are often enhanced when PCP is mixed with others substances, such as alcohol, stimulants such as cocaine, or depressants including narcotic medications. Mixing PCP with alcohol or other drugs can increase the risk of adverse effects and overdose.

PCP intoxication increases the risk of injuries from assaults, accidents, or falls 5. Chronic PCP use can lead to impairments in cognition, speech, and memory, and these deficits may last for months 5. It’s not uncommon for long-term PCP users to also experience 5, 17:

  • Heart attacks.
  • Respiratory issues.
  • Intracranial hemorrhage (bleeding inside the skull).
  • Rhabdomyolosis (the breakdown of muscle tissue, which can lead to kidney failure).
  • Depression.

Chronic PCP users may develop tolerance and require higher doses of the drug in order to experience desired effects 5. This can be dangerous since higher doses can cause seizures and coma 5.


Ketamine was designed as an anesthetic for both animal and human use, particularly in trauma or emergency situations. Nowadays, ketamine is abused for its dissociative effects and its popularity as a “club drug” is increasing, particularly among young adults and teens 18,20.

Ketamine is usually in a clear liquid or a white powder, the latter of which is placed in plastic bags, capsules, or glass vials 20. The drug can be snorted, smoked, injected, or mixed into drinks 20. It is often used in conjunction with cocaine, methamphetamine, amphetamine, or MDMA (Ecstasy) 20. Users will take ketamine repeatedly in a short period of time to prevent a “come-down” and maintain the psychoactive effects 21.

The “K-Hole”

Ketamine users can reach a level of intoxication known as a “K-hole,” which can be subjectively characterized as an out-of-body or near-death experience, although sometimes with a spiritual component 20,21.

Other slang phrases associated with ketamine intoxication, include “K-land,” which occurs at low doses and is a mellow experience, “Baby food,” in which the person is in a blissful, unmoving state, and “God,” in which the user encounters a higher power 21.

Street names for ketamine include 20:

  • Special K.
  • K.
  • Cat tranquilizer.
  • Kit kat.

The effects of ketamine occur rapidly and may include 20, 21, 22:

  • Sedation.
  • Numbness.
  • Hallucinations.
  • Delirium.
  • Psychosis.
  • Paranoia.
  • Disorientation.
  • Feelings of detachment.
  • Depression.
  • Agitation.
  • Amnesia.
  • Cognitive impairments.
  • Nausea.
  • Muscle stiffness.
  • Heart palpitations.
  • Dizziness.
  • Seizures.

Tolerance to ketamine use develops rapidly and there is evidence of physical dependence in chronic users 21. There are documented cases of withdrawal symptoms in some individuals, but insufficient research exists to support a ketamine withdrawal syndrome 21.

Are Hallucinogens Addictive?

Many people equate the term addiction with the experience of withdrawal symptoms, even though the two are separate issues. Hallucinogen users don’t tend to experience withdrawal symptoms with the cessation of use, due to the fact that these drugs don’t have a high potential for physical dependence. And although hallucinogens aren’t classically addictive, individuals can still suffer from problematic use that impairs their daily lives. Because of the ambiguity surrounding the term “addiction,” it is no longer used clinically in the diagnostic process 5.

Instead, the term substance use disorder is used to signify a psychiatric/psychological disorder that occurs in individuals who experience negative ramifications and issues controlling the use of drugs. The American Psychiatric Association lists specific diagnostic criteria for a hallucinogen use disorder, which encompasses both hallucinogen abuse and negative consequences of use.

Individuals who use these substances for non-medicinal purposes, have issues controlling their use, and experience negative consequences as a result of their use may be diagnosed with a hallucinogen use disorder or phencyclidine use disorder in the case of PCP use.

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If you or someone you love is abusing hallucinogens or other drugs, call to speak to a treatment support specialist about various recovery options.

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Rudolph C. Hatfield is a retired clinical neuropsychologist who specialized in assessing and treating neurological and psychiatric disorders. He currently writes about human behavior, the brain, and research methods for various mental health websites. Rudolph has also authored 2 books.

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