Do Hallucinogens Change the Brain?

Hallucinogens are substances that alter a person’s state of consciousness. They can affect a person’s mood, thoughts, perception, and experience of the self and the environment. The term hallucinogens can be misleading because not all drugs that induce hallucinations are hallucinogens and not all hallucinogens induce hallucinations. 

Additionally, different types of hallucinogens operate through different mechanisms. Classic hallucinogens such as DMT, LSD, psilocybin, and mescaline bind to serotonin receptors. Dissociative hallucinogens like phencyclidine (PCP) and ketamine block NMDA receptors. The last type of hallucinogens are entactogens. Entactogens, like MDMA, produce virtually no hallucinations but are associated with some psychedelic-like symptoms such as euphoria and positive emotions.

Although they bind to different receptors, classic and dissociative hallucinogens have similar psychological effects as they both interfere with the same circuitry in the brain. Hallucinogens disrupt sensory information in the cortico-striato-thalamic-cortical (CSTC) circuit which is responsible for directing attention, structuring time, discrimination between self and non-self, and ego formation. Hallucinogens disrupt the function of the thalamus in this circuit which is to prevent sensory overload in the cortex by restricting the flow of external and internal stimuli (Vollenweider, 2001). 

Altered states of consciousness associated with hallucinogens include oceanic boundlessness, anxious ego dissolution, and visionary hallucinations. Oceanic boundlessness is characterized by positive mood, positive experiences of derealization and depersonalization, and changes in one’s sense of time. On the other hand anxious ego dissolution is characterized negative experiences of derealization, thought disorder, and paranoia, and loss of body control (Milliere, 2017).

The experience of ego dissolution can be highly distressing or positive and life altering. Hallucinogens have been explored for their potential as treatments for depression. This effect is thought to be attributed to hallucinogens’ ability to influence one’s sense of self, connecting one to others, and seeing one’s experiences in a new light which can lead to self acceptance (Fischman, 2019). 

Despite how promising hallucinogens are in alleviating the symptoms of treatment resistant depression, their use does not come without risk (Goodwin et al., 2022). Hallucinogen Persisting Perception Disorder (HPPD) is a poorly understood phenomenon with no known treatment. It is characterized by long lasting visual disturbances after use of drugs. HPPD is not unique to psychedelics and is associated with the use of alcohol, cannabis, and other psychostimulants (Leo et al., 2013). HPPD is not common among those who use hallucinogens regularly. A questionnaire of over 16,000 hallucinogen users found that only 4.2% had lasting symptoms severe enough to seek treatment (Baggott et al., 2011).  

Hallucinogens do change the brain and can have a long lasting and transformative effect on people by altering the way they understand themselves in relation to others. They can be a powerful therapeutic tool, however additional research is needed to better understand the associated risks.


Baggott, M. J., Coyle, J. R., Erowid, E., Erowid, F., & Robertson, L. C. (2011). Abnormal visual experiences in individuals with histories of hallucinogen use: A web-based questionnaire. Drug and alcohol dependence, 114(1), 61-67.

Franz X. Vollenweider (2001) Brain mechanisms of hallucinogens and entactogens, Dialogues in Clinical Neuroscience, 3:4, 265-279, DOI: 10.31887/DCNS.2001.3.4/fxvollenweider

Fischman, L. G. (2019). Seeing without self: discovering new meaning with psychedelic-assisted psychotherapy. Neuropsychoanalysis, 21(2), 53-78.

Goodwin, G. M., Aaronson, S. T., Alvarez, O., Arden, P. C., Baker, A., Bennett, J. C., … & Malievskaia, E. (2022). Single-dose psilocybin for a treatment-resistant episode of major depression. New England Journal of Medicine, 387(18), 1637-1648.

Leo, H., Melanie, S., Martin, R., Anil, B., & Martin, G. (2013). Hallucinogen persisting perception disorder (HPPD) and flashback—are they identical?. J Alcoholism Drug Depend, 1(121), 2.

MacLean, K. A., Johnson, M. W., & Griffiths, R. R. (2011). Mystical experiences occasioned by the hallucinogen psilocybin lead to increases in the personality domain of openness. Journal of psychopharmacology, 25(11), 1453-1461.

Milliere, R. (2017). Looking for the self: phenomenology, neurophysiology and philosophical significance of drug-induced ego dissolution. Frontiers in human neuroscience, 245.

3 thoughts on “Do Hallucinogens Change the Brain?

  1. This is an interesting and well-informed article! I learned that (1) not all drugs that induce hallucinations are hallucinogens and not all hallucinogens induce hallucinations, and (2) hallucinogens can have a long-lasting and transformative effect on people. These are very important things that we should be aware of when thinking about “hallucinations” which should not be considered the same as hallucinogens. The article also contains a lot of great pictures (especially the second one) that help us better understand the complicated information.


  2. Sophia, wow – what an insightful post! Your exploration of hallucinogens was captivating. As someone who has grappled with depression and existential angst for years, the idea of ego dissolution sounds terrifying and fascinating. I can see how that kind of radical shift in perception could be healing under the right circumstances. I appreciated how balanced your analysis was. You acknowledged the promise of hallucinogens for treatment and the real risks, like HPPD. That kind of nuanced perspective gives your writing credibility. Too often, people are either overly enthusiastic or overly fearful regarding psychedelics. You struck a thoughtful middle ground.


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