The mode of action of psilocybin and meditation

Peter MolemanArticles, Psychiatry, The world within your headLeave a Comment

Translated by Rumia Bose

Psilocybin has long been known as a psychedelic for recreational use, but has returned to the spotlight recently as a (possible) medicinal drug, especially as a potential antidepressant. What surprises me is that it may also be effective in the treatment of various anxiety disorders, post-traumatic stress disorder, addictions and obsessive-compulsive disorder (OCD).
What is the mechanism of action that might make it effective against such a wide variety of psychiatric disorders1NB: psilocybin should definitely not be used by people sensitive to psychotic disorders or experiences? Could it be similar to the way it works for recreational use, where a large variety of experiences have been described, ranging from visual distortions, a feeling of happiness, a variety of emotions and even to what has been called “ego-dissolution”? It is not easy to say what happens in these cases. Our knowledge of how the brain works has in the meantime progressed so far that it is now clear how psilocybin works. And it appears that meditation works in approximately the same way. This knowledge is not only of interest to neuroscientists, but also makes clear what positive effects one can expect from psilocybin and meditation, and the risks of their use.

The predictive organ

In order to understand how psilocybin works we must first make clear that the brain is not an analysing machine, but a predictive organ. This has been described in my blog Hallucinations: seeing what you expect, and can be summarised as follows. You form a model of the world in your head based on all your experiences, everything you have been through and learnt since birth. You use this model to predict what is going to happen. In “Hallucinations: seeing what you expect” you will find relatively simple examples of what happens when you predict what you are about to percieve. Humans have however developed much more complex and abstract functions not directly related to perception of the outside world. These are also handled by the predictive organ.
I am now writing this blog; this has little to do with what the outside world looks like at this moment, and the prediction about what is about to happen there. But writing too has to do with prediction and verification. I think up the following sentence in my explanation. I write it down; the prediction is obviously that it is correct. I then read the whole paragraph, and it often turns out not to be right. This can be something evident, like an obvious thought error. But often it is more a feeling: this paragraph is not right. Sometimes I can’t put my finger on the problem, even after reading it through a few times. I need to go away and do something else for a bit and then take a fresh look at the paragraph. Often this leads to my spotting the problem.
What is happening here? I couldn’t figure out what the problem was at first, because I clung to the prediction on the basis of the model in my head. That model contains the total of my thoughts on how psilocybin works (see Who is a believer? I am! how this model is formed). But there was a hitch in this, which is why the last sentence was not right. Only when I had taken some distance from the text could I see it in perspective. Once I have corrected the last sentence, or the whole paragraph, so that it is as it should be, then the model in my head is also changed, or rather adjusted. My further predictions are on the basis of the adjusted model.

The rigid predictive organ

The story above illustrates that I could not just alter the model in my head at will. I held on to it a touch rigidly. Perhaps it was because I did not like the idea that the model was not quite accurate. Perhaps it hurt my ego a bit. It may seem as if I do and think all this consciously, but in fact it is all processed nonconsciously. In this context I should point out that it would lead to chaos if we had to discard the model in our head each time there was a tiny discrepancy. There has to be a balance between rigidity and flexibility.
Excessive rigidity can have its disadvantages too. Someone with an obsessive-compulsive disorder, for instance, fixates onto the idea that it is the end of the world if he loses something, or that he will develop a serious infection if he does not wash his hands for four hours a day. If you ask such a person about this, he knows very well that this is not true. But he is still unable to let go of the model in his head and adjust it. Whereas this is what is required to act differently, because you always act in accordance with the prediction based on that model. And if you suffer from depression, then one of the common symptoms is that you foresee problems cropping up everywhere, or think that things will go wrong. The fact that things work out better than predicted will lead to an adjustment of the model and improved mood in a person without depression, but will most often not have this effect in a depressed person.


Psilocybin tweaks your predictive organ a little. It makes it less rigid, mainly affecting the highest levels, where the most abstract predictions are formed. Read about the case of Adam Strauss who vividly describes te effect of psilocybin on his OCD. As explained above in the paragraph “The predictive organ” predictions of what you are about to see are relatively simple as compared to predictions related to e.g. writing about the workings of psilocybin. The former I call a lower level and the latter a higher, or even the highest level of the prediction organ. The effect of psilicybin on the highest levels is associated with moderate doses, (somewhat) lower than the usual doses for recreational use. Visual distortions from psilocybin originate in the lower levels of the predictive organ with recreational use in the higher dose range, and are largely absent with the use of relatively low doses.
The effects vary in an unpredictable way per person, which makes sense, as the individual variation regarding the model in our head is most apparent in the higher levels. Everybody has a more or less similar model in his head of what a chair or a table looks like. But when it comes to abstract issues, your model may be quite different from mine. Imagine you are about to take psilocybin for the first time. Your parents may have told you drugs are dangerous, or not. Or your friend described his overwhelming and positive experiences with psilocybin, or he may have described his negative experiences. You may be of a slightly anxious nature, or not at all. Predictions of the effect of psilocybin will differ markedly due to how these experiences have formed your predictive organ. The effect of psilocybin depends on the current state of the model in your head, specifically at the highest level.

…and meditation

Meditation does almost the same thing as psilocybin. The main difference is that meditation brings about a much slower and more gradual alteration in the predictive organ. Eight years ago I started Vipassana meditation, with a ten-day course once a year and daily meditation practice at home. During the ten-day course in the centre in Belgium I feel a lot happening with me. But once back home the effect limits itself to my being less irritable and perhaps less stress-prone. I have often thought that I might as well give up the home practice altogether.
But this changed when I was diagnosed with cancer of the bladder. A lot of people assume that I was enormously shocked, or that I am stressed about how things will develop and play out. But that is not really the case. One of the most important things you learn with Vipassana meditation is equanimity. You learn to feel what is going on in your body and register this as an observer without reacting to it. This process is not always pleasant, but you also learn that all things come and go, so the unpleasant experience will pass too. To give an example: after one of the hospital procedures I had extremely painful spasms in my bladder when urinating. The first time I experienced these I was doubled up in agony. The next time I had to go, I applied my Vipassana technique to observe the spasm. I felt the same obnoxious sensation in my bladder, but without the experience of pain.
This equanimity is an acquired alteration of my predictive organ, of the model in my head. After a lot of meditation practice I now manage with reasonable success to live in the present. The highest levels of my predictive organ are far less dominant, therefore reducing the previously large role played by long term predictions. In due time I will have further tests to show if the first (relatively mild) course of treatment has been successful. I wait for this, but do not try to look further than this point. I know that in a few years’ time I may be cured, or dead. But this does not strongly affect my mood or emotions.

The benefits of psilocybin and meditation …

Psilocybin is not an antidepressant, or a drug against addiction, anxiety disorders or OCD. It makes your predictive organ less rigid, which can help with all these disorders. It changes you as a person, whether you have a disorder or not. That is, if the effect lasts. It is not so that your model of the world will adjust of itself if your predictive organ is tweaked. And the newly acquired improved flexibility of your predictive organ needs to last. Which you need to work on. A session2I don’t use the expression “trip” here, because I reserve it for recreational use with higher doses needs to take place in the right circumstances in the presence of somebody who knows how to handle your reactions.
Recreational users often have similar experiences, but lose the effect until they use again. I have met people at the meditation centre who have used recreational psychedelics and who now practice Vipassana meditation. They describe having experiences with psychedelic use which are similar to those with meditation, but in the first case like a storm or a blow with a hammer, whereas meditation has brought about a much more gradual but lasting change in their life. This illustrates that psychedelic experiences do not get built into your model of the world just like that.

… and the dangers

Both psychedelics and meditation are not without risk. I have so far attended eight 10-day Vipassana courses. At each course a few of the hundred participants drop out early, some of them because they turn suicidal or psychotic. And this is despite the fact that you are only allowed on the course after screening by the course administration to be sure that you do not have severe mental health issues3based on your own information, no doctor’s information is asked for. I think that things can go wrong if the increased flexibility goes out of control. This has to do with “ego dissolution”. You experience your ego as a unified, constant whole, which constitutes you. But your ego is actually a construct by your brain, of your predictive organ (see The Ego is dead, long live the ego). When the integrity of your predictive organ is lost, when the flexibility goes out of control, strange things can happen.
Such unpredictable events also occur with psychedelics, perhaps even more often, although it is difficult to find data on this. This is the reason that I am concerned about commercial use of psilocybin or other psychedelics, or unsupervised use now that it is such a hype. The same also holds for the learning of meditation techniques without expert instructions and supervision.


Psilocybin and meditation can have a huge impact on our predictive organ. This can make a new person of you, provided it is used the right way. I am curious as to whether psilocybin will prove to be a breakthrough in clinical psychiatry. Personally I hold the opinion that not every patient with a depression, anxiety disorder, post-traumatic stress disorder, addiction or obsessive-compulsive disorder will experience benefits brought about by psilocybin or meditation. I think that depends on where the rigidity of the prediction organ has arisen. If this is at the higher levels, then psilocybin or meditation may have a better chance to work positively than when the rigidity has arisen at a lower level. At least where mindfulness is concerned, one can speak of disappointing clinical results. Whether this is related to the form of meditation, the manner of delivery or patient selection, I could not say.


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