How Do Hallucinogens Work?

Male face silhouetted in sky as if a hallucination

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Hallucinogens are a class of drugs that cause profound distortions in a person's perceptions of reality, otherwise known as hallucinations. While under the influence of hallucinogens, a person might see images, hear sounds, or feel sensations that seem to be real but aren't.

Hallucinogens, also known as psychedelics, work by disrupting how neurotransmitters work in the brain. Many hallucinogens have chemical structures similar to those of natural neurotransmitters, like acetylcholine, serotonin, or catecholamines.

Hallucinogens can be man-made, or they can come from plants or mushrooms or extracts from plants and mushrooms. Generally, they are divided into two types: classic hallucinogens and dissociative drugs. Either type of hallucinogen can cause people to have rapid, intense emotional swings.

This article discusses the different types of hallucinogens and their effects. It also covers how they work and their potential therapeutic uses.

Classic Hallucinogens

Some of the classic hallucinogens include:


Sometimes called hoasca, aya, and yage, ayahuasca is brewed from plants containing DMT along with an Amazonian vine that prevents the normal breakdown of DMT in the digestive system. It is usually consumed as a tea.


Dimethyltryptamine, also known as Dimitri or DMT, is a natural chemical found in some Amazonian plant species, but it can also be chemically synthesized. It usually comes as a white, crystalline powder that is vaporized or smoked in a pipe or bong.


D-lysergic acid diethylamide (LSD) is a manmade chemical made from ergot, a fungus that grows on certain grains. It is probably the most powerful hallucinogen available, producing hallucinations, changes in the way reality is perceived, and altered moods.

It comes as a white powder or clear liquid and has no color or smell. It can come in capsules, but most often comes on small squares of blotter paper or gelatin that people place on the tongue or swallow to take a "trip."

What Is the Strongest Form of Hallucinogens?

LSD is one of the strongest hallucinogens. LSD produces some of the most significant mood and perception-altering states in people who use it.


Methylenedioxymethamphetamine (MDMA) is a synthetic drug that is derived from amphetamine. It is also known as ecstasy or "molly." It works by increasing the activity of the neurotransmitters dopamine, serotonin, and norepinephrine. It acts as both a hallucinogen and a stimulant and produces enhanced sensory perceptions, decreased anxiety, and feelings of mental stimulation.


This natural substance is the main ingredient in the peyote cactus. The top of the spineless peyote cactus plants has disc-shaped "buttons" that contain mescaline. The buttons are dried out and then either chewed or soaked in liquid to produce an intoxicating drink. Mescaline can also be made through chemical synthesis.


Psilocybin and psilocin are natural substances found in hallucinogenic mushrooms. In large enough doses, psilocybin can produce effects very similar to the powerful hallucinogen LSD. "Shrooms," as they are sometimes called, can be used either fresh or dried. They are normally eaten, mixed with food, or brewed like tea for drinking.

Tetrahydrocannabinol (THC)

The active ingredient in marijuana is delta-9 tetrahydrocannabinol or THC, which acts on cannabinoid receptors found in brain regions that influence learning, memory, appetite, coordination, and pleasure.

THC is just one of more than 400 different active substances—and 60 different cannabinoid molecules—contained in marijuana. Widely used as a recreational and medicinal substance, marijuana has been found to cause paranoia or anxiety as well as hallucinations, especially in adolescents who use the drug regularly. Time distortion, which is a symptom of marijuana use, is also part of hallucination.


Classic hallucinogens include ayahuasca, DMT, LSD, MDMA, mescaline, psilocybin, and THC.

Dissociative Drugs

Dissociative drugs are a class of hallucinogens that affect the perception of sight and sound. In addition to causing these perceptual distortions, they also produce feelings of dissociation and detachment from the environment and/or the self.

Dextromethorphan (DXM)

Dextromethorphan, also known as DXM or robo, is a cough suppressant and expectorant that is often included as an ingredient in over-the-counter cold medications. When taken in doses higher than recommended, it may produce hallucinogenic effects including perceptual disturbances, feelings of euphoria, and disruptions in motor control.


Ketamine, also known as K or Special K, is a type of dissociative drug that is used as an anesthetic in humans and animals. When used recreationally, it often creates a deep dissociative state as well as visual disturbances, disorientation, euphoria, and sedation.


PCP is a dangerous manmade substance that was originally developed as an anesthetic but was discontinued for human use in 1965 due to side effects. It is now an illegal street drug sold as a white powder or in liquid form. It can be snorted, injected, smoked, or swallowed.

It produces hallucinations and "out-of-body" sensations. Usage, especially in large doses, can be life-threatening and lead to serious mental health problems.


Salvia is a hallucinogenic herb that is sometimes used recreationally to mimic the effects of LSD and ecstasy. Salvia is fast-acting, with effects that don't last long. Salvia contains a chemical called salvinorin A, which acts on receptors in the brain to produce hallucinations. When using the drug, people may experience dissociation, an altered sense of reality, and changes in self-awareness.


Some hallucinogens are classified as dissociative drugs. These include DXM, ketamine, PCP, and salvia.

How Hallucinogens Impact the Brain

Classic hallucinogens disrupt communication between chemicals in the brain. One of these chemicals is serotonin, which affects mood, sleep, hunger, body temperature, sensory perception, sexual behavior, and intestinal control.

Because classic hallucinogens affect sensory perception, people who use these drugs may feel, see, or hear things that aren't really there.

Other side effects of classic hallucinogens—such as lack of sleep, excessive sweating, and panic—are explained by this disruption in serotonin, since serotonin controls the related bodily functions.

Dissociative hallucinogenic drugs also disrupt chemicals in the brain and spinal cord; but instead of serotonin, they primarily affect the brain's glutamate system. The chemical glutamate affects functions such as pain perception, emotion, and learning and memory.

Effects of Hallucinogenic Drugs

Hallucinogens can produce a range of effects that vary in terms of intensity, duration, and long-term effects. These drugs affect how people think, including their perceptions of reality and the self.

Short-Term Effects

The short-term effects of hallucinogens typically begin within 20 to 90 minutes of taking substances. These effects may be brief, lasting around 15 minutes in some cases. In other cases, these short-term effects may last as long as 12 hours.

Common short-term effects include:

  • Anxiety or panic
  • Changes in appetite
  • Changes in the perception of time
  • Feelings of euphoria or relaxation
  • Increased heart rate
  • Intensified sensory experiences and emotions
  • Nausea
  • Paranoia
  • Psychosis
  • Sleep disturbances

A person may also experience hallucinations in which they see, hear, or feel sensations that aren't really there. When these hallucinations are unpleasant or distressing, people often call it a "bad trip." Unfortunately, a bad trip can last anywhere from 15 minutes to 12 hours, depending on the quantity and type of hallucinogen a person uses.

Long-Term Effects

Hallucinogens may also produce long-term effects in some cases. According to the National Institute on Drug Abuse, these effects are rare.

  • Hallucinogen persisting perception disorder (HPPD) involves the recurrences of experiences associated with using the drug including visual disturbances and hallucinations. Such flashbacks can occur suddenly with no warning and may occur more than a year following drug use.
  • Persistent psychosis may occur in some cases. Symptoms include mood changes, paranoia, disorganized thinking, and visual disturbances. 

Dependence and Withdrawal

It is possible to develop a dependence or even addiction to some hallucinogens. However, some hallucinogens have more potential for dependence than others.

Hallucinogens Withdrawal Symptoms

Research has found that hallucinogens like PCP may be addictive and even cause withdrawal symptoms. These symptoms include cravings for the drug, headaches, and excessive sweating.

The repeated use of hallucinogens puts a person at risk of developing a tolerance. A tolerance to a drug means that you need to use a greater quantity of the drug over time to achieve the same effects.

LSD is known to produce a tolerance in people who use it; it may also produce a tolerance to other types of hallucinogens such as psilocybin.

More research is needed to understand the potential for dependence, addiction, and withdrawal in the different types of hallucinogenic drugs.

Therapeutic Uses

The use of hallucinogens traces back to indigenous cultures in Africa, South America, North America, and Central America.

Spiritual leaders would often administer or oversee the use of plant-based medicines such as peyote or psilocybin. Psychedelics were seen to help people get closer to the spiritual realm, which would also aid in any physical illness.

Researchers in the United States in the 1960s began to produce scientific reports on drugs like LSD and psilocybin and their potential as psychiatric treatments. In addition, these drugs were gaining popularity in the U.S. counterculture—the use of hallucinogens was reflected in music, literature, and film during this time.

In recent years, there has been a resurgence of interest in the therapeutic potential of some hallucinogens.

Psychedelic therapy is a type of treatment that uses psychedelic substances such as LSD, psilocybin, and ketamine in a controlled setting under the supervision of a therapist to treat mental health issues like anxiety, post-traumatic stress disorder (PTSD), and depression.

Studies suggest that such substances may be helpful for treating some mental health conditions. For example, one study found that psilocybin combined with behavioral interventions was helpful for relieving anxiety and depression.

Though psychedelics are still controlled substances and illegal under federal law, the following events have contributed to the growing conversation surrounding their therapeutic use:

  • In 2019, the FDA approved a ketamine-derived nasal spray for treatment-resistant depression
  • In 2020, Oregon passed a bill legalizing psilocybin for medicinal use
  • In 2023, the FDA plans to fast-track approval for MDMA as a PTSD treatment
  • Though LSD remains illegal under law, it has become a popular drug in the "microdosing" movement

Benefits and Risks of Hallucinogens

Research has found that there are many potential benefits to using hallucinogens. But, it's important to note that there are risks to using any drug—especially without the supervision of a health professional.

Benefits may include:

  • LSD, psilocybin, and ayahuasca has been found to improve symptoms of depression, anxiety, and eating disorders for some people.
  • Hallucinogens are connected with greater levels of spirituality which, in turn, may improve emotional stability.
  • Psilocybin may help decrease stress and anxiety in people coping with life-threatening illnesses such as cancer.
  • Psilocybin, along with psychotherapy, has been found to help some people cope with the grief of losing a loved one and existential distress.
  • MDMA has been found to help some autistic individuals cope with social anxiety.
  • MDMA and psychotherapy may help reduce symptoms of PTSD.

Risks may include:

  • Even under clinical supervision, adverse effects have been recorded in people receiving psychedelic treatment. These effects include acute increase in anxiety and fear, as well as an increase in blood pressure and heart rate.
  • Without appropriate supervision, hallucinogens may cause fear and result in dangerous behavior such as fleeing the site of treatment.
  • Psilocybin (and potentially other hallucinogens) may cause delayed-onset headache.
  • MDMA (and potentially other hallucinogens) may cause adverse cardiovascular effects such as tachycardia.

Especially if you're using hallucinogens without any medical supervision, you may put yourself at risk in a variety of ways. For instance, you may experience disruptions in motor control but try to drive a car—putting yourself and others at risk of injury on the road.

In some cases, during a bad trip, you might try to escape from distressing sensory hallucinations and put yourself at risk of physical injury. Someone with anxiety may accidentally worsen their symptoms if they have a bad trip as well.


Hallucinogens are drugs that alter thoughts, perceptions, and feelings. While using these substances, people may experience hallucinations, where they have sensations or perceptions that are not real.

Experts do not know exactly how hallucinogens produce their effects, but they are believed to affect neurotransmitters in the brain, including serotonin and glutamate. Research also indicates that some hallucinogens may have therapeutic potential in the treatment of conditions such as anxiety and depression.

If you or a loved one are struggling with substance use or addiction, contact the Substance Abuse and Mental Health Services Administration (SAMHSA) National Helpline at 1-800-662-4357 for information on support and treatment facilities in your area.

For more mental health resources, see our National Helpline Database.

Frequently Asked Questions

  • What is the difference between narcotics and hallucinogens?

    Narcotics are drugs that include opiates, opioids, and synthetic opioids. Some of these drugs have medical uses, particularly for pain relief. They can also produce physical dependence and have a high potential for addiction. While hallucinogens affect thinking and perception, narcotics tend to produce a variety of effects including blocking pain signals and creating feelings of euphoria.

  • How do hallucinogens affect the brain?

    According to the National Institute on Drug Abuse, hallucinogens are believed to produce their mind-altering effects due to disruptions in the neurotransmitter serotonin. By altering how serotonin acts on neural circuits in the brain, particularly in regions associated with perception, mood, and cognition, people experience changes in how they think and perceive reality.

  • What is the difference between hallucinogenic and psychedelic?

    Hallucinogens and psychedelics are the same. Psychedelic is another word for hallucinogenic, meaning affecting thinking, senses, perceptions, and emotions. 

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Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Buddy T
Buddy T is an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism.