The National Institute on Drug Abuse (NIDA) reports that the use of hallucinogens causes an alteration of perception and cognition (the process of thinking) that results in a significant distortion of the real world. Perceptions refer to one’s interpretation of sensory input, and one’s subjective interpretation of events when using hallucinogens results in an alteration of one’s perceptions that differ markedly from the types of experiences that other drugs produce. For example, drugs that are central nervous system depressants result in a significant slowing of the actions of the brain and spinal cord, and this affects one’s perceptions; however, it does not significantly alter them to the point of totally distorting reality.

What Are Hallucinogens?

Hallucinogens make up a specific class of drugs, and there are actually a number of different compounds that qualify as hallucinogens; however, some other drugs alter perceptions significantly but are not classified as hallucinogens. Familiar drugs like cannabis may alter sensory perceptions, and many wrongly believe cannabis products to be hallucinogens, but cannabis use does not result in the severe alterations of perception that are produced by hallucinogens, such as hallucinations, dissociative effects, and distortions of the perception of space and time.

Taking a hallucinogen will commonly lead to the experience of hallucinations in nearly all individuals who take them, and this is not true with other classes of drugs. The most common form of hallucinations that occurs from using these drugs are visual hallucinations (seeing things that are not there), but other types of hallucinations, such as auditory hallucinations, tactile hallucinations, etc., can also occur. Other effects that can occur from using these drugs include dissociative experiences (the distorted perception that one is detached from one’s body or one is detached from reality), alterations in the perception of time and space, and mixed sensory experiences (e.g., synesthesia, which is the perception that one’s senses are mixed, such as one can hear colors). Many individuals believe that use of hallucinogenic drugs expands one’s consciousness, and some of these drugs have long histories of use during certain types of religious ceremonies.


Different hallucinogenic drugs have different mechanisms of action, but many of these drugs primarily affect the neurotransmitter serotonin. NIDA, SAMHSA, and other sources often divide hallucinogenic drugs into two broad subcategories: classic hallucinogens and dissociative hallucinogens.

Classic Hallucinogens

Classic hallucinogenic drugs will typically produce the perception of enhanced senses (e.g., sounds are perceived as being more acute or colors are perceived as being brighter), alterations in the sense of time and space (e.g., time appears to move extremely slowly), and hallucinations. Some individuals may also experience dissociative experiences with these drugs, but they are less likely to produce them in most individuals.

  • LSD: The drug LSD (lysergic acid diethylamide) was originally sympathized in 1938 in an effort to develop drugs that would speed up the process of childbirth and reduce potential bleeding. The drug was found to have no usefulness for these purposes, and further research with the drug was discontinued for approximately five years. In the 1940s, further research on the drug was initiated, and it was found that the drug produced very powerful visual hallucinations and mood-altering effects. These findings resulted in the drug being marketed as a potential therapy drug for use by psychiatrists.

    Its use became extremely popularized in the 1960s and 1970s as part of the drug counterculture. It was at this time that the drug was taken off the market and made illegal.The drug produces very powerful effects even though it is typically taken in extremely small doses (100-200 micromilligrams is considered to be the average dose) and the effects are relatively long-lasting (up to 12 hours). The primary effects that occur when one takes LSD are:

  • Feelings of euphoria
  • Enhanced mood
  • Marked alterations in the sense of time
  • Visual hallucinations and/or other hallucinations
  • Heighted perceptional acuity
  • Enhancement of other emotional states

The effects of LSD often appear to be dependent on the context, and some individuals may experience issues with anxiety or depression. Research looking at case studies of individuals who took extremely high doses of LSD suggest that fatalities due to overdose as a result of taking LSD alone are unknown. In the few known cases where people who took large amounts of LSD died involved the use of multiple drugs; therefore, LSD use alone cannot be designated as a causal factor in these fatalities.

lysergic acid diethylamide

Case studies involving individuals who took extremely high doses of LSD indicate that the effects of overdose can typically be addressed medically, and there are no long-term effects. The effects are typically described as a rise in body temperature, decreased breathing rates, some gastrointestinal issues, and potential unconsciousness or coma. A very small proportion of chronic LSD users experience a disorder known as hallucinogen persisting perception disorder, which consists of the repeated experience of drug flashbacks after one has stopped using the drug for a significant period of time. While these effects can be stressful, they are not considered to be potentially dangerous, and treatment for this disorder occurs on a case-by-case basis.

While the DEA maintains that LSD has no utility for medical purposes, there is research investigating its use in the treatment of certain psychiatric disorders.

  • Peyote/mescaline: Peyote is a small spineless cactus that is grown in the southwestern United States and Central America. The psychoactive substance in peyote is mescaline, which can also be produced artificially. The protrusions from the cactus are cut off the plant, dried out, and either chewed, soaked in some other substance and consumed as a beverage, or smoked. Artificially produced mescaline can be taken in tablet or liquid form.The psychoactive effects of mescaline will typically begin an hour or two after one takes it and can last up to 12 hours. These effects are reported as:
  • Heightened sensory perceptions
  • Vivid hallucinations
  • Alterations in the perception of time
  • Synesthesia
  • Difficulty focusing one’s attention
  • Mood swings (can include extreme panic)
  • Psychotic behaviors
  • Dizziness
  • Nausea
  • Increased blood pressure and/or heart rate
  • Weakness
  • Fever and/or chills
  • Extreme sweating
  • Pupil dilation
  • Weakness

Peyote is one of the oldest hallucinogenic drugs. It was used by Native American groups and even the Aztec Indians for medicinal reasons and in religious services. Certain Native American groups in the United States still have the legal right to use it in their religious services. There do not appear to be serious physical effects associated with taking high doses of peyote.

Peyote mescaline
  • Psilocybin: Psilocybin (4-phosphoryloxy-N, N-dimethyltryptamine) is the psychoactive substance that is contained in hundreds of different types of mushrooms. These are often referred to as “magic mushrooms” or “psychedelic mushrooms.” These mushrooms are grown in portions of the United States, Mexico, and South America. The mushrooms are typically dried out and eaten but sometimes may be consumed in beverages, such as tea or alcoholic drinks.The effects of psilocybin are reported as:
  • Hallucinations
  • Alterations in the sense of time (time moving very slowly)
  • Euphoria
  • Some cases of mild dissociation
  • Increases in heart rate and blood pressure
  • Shakiness and tremors
  • Impairments and physical coordination
  • Dilated pupils

Dissociative Hallucinogens

Dissociative hallucinogens can produce the effects of the classic hallucinogens but are also likely to result in experiences of dissociation that do not commonly occur with classic hallucinogens. These experiences are primarily feelings of depersonalization (being detached from one’s body) and derealization (the perception that things are not real or that one is separate from reality).

  • Ketamine: Ketamine is a drug that was designed to be an anesthetic and an analgesic but was discontinued as a regular anesthetic due to potentially dangerous side effects. It still has some medicinal uses, including uses as an anesthetic in specialized cases, and it is being researched regarding its usefulness in treating clinical depression that is unresponsive to other forms of treatment. Ketamine is a bit different than other hallucinogens in that it acts on the excitatory transmitter N-methyl-d-aspartate (NDMA) and blocks its function in the brain as well as acts on a number of other neurotransmitters. Ketamine was a very popular rave or club drug in the 1990s and early 2000s but its use has decreased.

    The effects of ketamine are reported as:

  • Dissociation, issues with attention, and memory loss
  • A hypnotic state that results in confusion and sedation at low to moderate doses
  • Hallucinations and even unconsciousness at higher doses
  • Pain reduction
  • Increased heart rate, blood pressure, and body temperature
  • Significant cognitive effects, especially issues with attention and memory, with chronic use
  • PCP: PCP (phencyclidine) was developed to be used as an anesthetic but due to potentially dangerous side effects, it is no longer used for that purpose. PCP is commonly snorted on the street. It is not a common drug of abuse, but it is potentially very dangerous.

The effects of taking PCP depend on the amount an individual uses. People taking low doses of PCP will often present as being intoxicated (under the influence of alcohol) without the smell of alcohol. This includes slurred speech, problems with walking, issues with balance, giddiness, and bloodshot eyes. Other effects include dissociative effects (derealization and/or depersonalization), changes in one’s sense of one’s body, and even aggression. Some people may believe that they are invulnerable, and this can lead to potential dangerous behaviors. Those taking moderate doses will appear heavily sedated and may even be unconscious. High doses can result in the development of seizures and comatose states.


Research indicates that chronic use of PCP is associated with irreversible damage to the brain, and that mixing PCP with other drugs, such as alcohol or stimulants, can enhance its effects.

  • DMT: DMT (N, N-Dimethyltryptamine) comes from the ayahuasca plant, which is a tropical vine in central South America. The leaves and shoots from the plant are made into a tea or can be ground up and chewed. Illicit users may get the substance in powder or pill form and take it in that manner. The effects of DMT include:
  • Enhanced sensory perception
  • Hallucinations and extreme mood alteration that can include euphoria and anxious statesio
  • The perception of improved focus
  • Alterations in the sense of time
  • Increased heart rate, body temperature, blood pressure, and respiration rate
  • Nausea and vomiting
  • Potential psychosis

Abuse Potential of Hallucinogens

The abuse potential for most hallucinogens is considered to be relatively low compared to other drugs, such as narcotic painkillers, alcohol, cocaine, etc. For most of these drugs, there is a rapid development of tolerance, but there is no identified withdrawal syndrome (exceptions to this may be PCP and ketamine). Withdrawal symptoms that are reported to occur appear to be primarily emotional in nature and are not considered to be potentially life-threatening. Nonetheless, due to the severe alterations in reality that these drugs produce, there is always the potential that an individual under the influence of these drugs may engage in potentially dangerous behaviors due to poor judgment, having a bad trip, or reactions that occur as a result of extreme emotional states that can be produced by these drugs (e.g., panic).

The American Psychiatric Association lists separate criteria for a phencyclidine use disorder and for other hallucinogenic use disorders, highlighting the potential dangers associated with use of PCP.

Individuals who develop substance use disorders to hallucinogenic drugs require targeted treatment aimed at their specific case. They need to become engaged in a long-term treatment program, complete with an aftercare plan, to effectively achieve sustained recovery.