From relaxed beliefs under psychedelics (REBUS) to revised beliefs after psychedelics (REBAS)

This single-blind (n=11) study with healthy participants shows that confidence in negative self-beliefs decreased after a high dose of psilocybin (25mg) which predicted increases in well-being four weeks later. This provides the first psychological (vs neurological) information on the validity of the REBUS model.

Abstract of From relaxed beliefs under psychedelics (REBUS) to revised beliefs after psychedelics (REBAS)

Background: The Relaxed Beliefs Under pSychedelics (REBUS) model proposes that serotonergic psychedelics decrease the precision weighting of neurobiologically-encoded beliefs, and offers a unified account of the acute and therapeutic action of psychedelics. Although REBUS has received some neuroscientific support, little research has examined its psychological validity. We conducted a preliminary examination of two psychological assumptions of REBUS: (a) psychedelics foster acute relaxation and post-acute revision of confidence in mental-health-relevant beliefs; (b) this relaxation and revision facilitates positive therapeutic outcomes and is associated with the entropy of EEG signals(an index of neurophysiological mechanisms relevant to REBUS).

Method: Healthy individuals (N=11) were administered 1 mg and 25 mg psilocybin 4-weeks apart. Confidence ratings for personally held negative and positive beliefs were obtained before, during, and 4-weeks after dosing sessions. Acute entropy and self-reported subjective experiences were measured, as was well-being (before and 4-weeks after dosing sessions).

Results: Confidence in negative self-beliefs decreased following 25 mg psilocybin and not following 1 mg psilocybin. Entropy and subjective effects under 25 mg psilocybin correlated with decreases in negative self-belief confidence (acute and 4-weeks after dosing). Particularly strong evidence was seen for a relationship between decreases in negative self-belief confidence and increases in well-being at 4-weeks.

Conclusions: We report the first empirical evidence that the relaxation and revision of negative self-belief confidence mediates positive psychological outcomes; a psychological assumption ofREBUS. Replication within larger and clinical samples remains necessary. We also introduce a new measure, the Relaxed BEliefs Questionnaire (REB-Q), for examining the robustness of these preliminary findings and the utility of the REBUS model.”

Authors: Richard J. Zeifman, Meg J. Spriggs, Hannes Kettner, Taylor Lyons, Fernando E. Rosas, Pedro A. M. Mediano, David Erritzoe & Robin L. Carhart-Harris

Summary of From relaxed beliefs under psychedelics (REBUS) to revised beliefs after psychedelics (REBAS)

We previously covered this study in July 2022, when it was released as a pre-print.

The article opens by discussing the growing interest in psychedelic therapy as a transdiagnostic approach to improve various mental health outcomes, such as reducing anxiety, depression, and suicidal ideation, as well as enhancing overall well-being. The researchers introduce the concept that understanding the mechanisms of change in psychedelic therapy could lead to more tailored and effective treatments. They highlight the theoretical framework known as the RElaxed Beliefs Under pSychedelics (REBUS) model, which builds on Bayesian hierarchical predictive processing. In this context, the term “Bayesian” refers to a statistical framework that incorporates prior beliefs with new evidence, while “hierarchical predictive processing” describes how the brain processes information in layers of predictions and corrections. The REBUS model suggests that psychedelics induce an “entropic” brain state—that is, a state of increased neural randomness and flexibility—which reduces the precision or confidence of deeply held, maladaptive beliefs, such as negative self-perceptions.

The introduction further explains that this temporary relaxation of overconfident beliefs may allow for a post-acute revision, termed REvised Beliefs After pSychedelics (REBAS). The researchers propose that this mechanism could be key to the sustained improvements in mental health observed after psychedelic treatment. They note that while neurobiological research has identified increased neural entropy and reduced hierarchical organisation following psychedelic administration, the psychological counterpart—specifically the decrease in confidence in negative self-beliefs—has not been thoroughly investigated. The article thus sets out to examine whether a dose of psilocybin can acutely reduce the confidence in negative self-beliefs (belief relaxation) and whether these changes persist, leading to a lasting revision of such beliefs (belief revision). In addition, the study aims to explore how these psychological changes relate to neurobiological markers like neural entropy, the intensity of acute unitive experiences, and subsequent improvements in well-being.

Results

Self and Other (Negative/Positive) Belief Confidence

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Find this paper

From relaxed beliefs under psychedelics (REBUS) to revised beliefs after psychedelics (REBAS)

https://doi.org/10.1038/s41598-023-28111-3

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Cite this paper (APA)

Zeifman, R. J., Spriggs, M. J., Kettner, H., Lyons, T., Rosas, F. E., Mediano, P. A., ... & Carhart-Harris, R. L. (2025). From relaxed beliefs under psychedelics (REBUS) to revised beliefs after psychedelics (REBAS). Scientific Reports15(1), 1-12.

Study details

Compounds studied
Psilocybin

Topics studied
Healthy Subjects

Study characteristics
Single-Blind Within-Subject

Participants
11 Humans

Authors

Authors associated with this publication with profiles on Blossom

Richard Zeifman
Richard Zeifman is working at Imperial College London on psychedelics as a novel intervention for suicidality.

Hannes Kettner
Hannes Kettner is a Ph.D. student at the Imperial College Centre for Psychedelic Research and a Scientific Officer at MyDelica. He is interested in studying real-world psychedelic use, including ceremonies, retreats, burns, and what we can learn from them about creating a positive set & setting.

Taylor Lyons
Taylor Lyons is completing her PhD at Imperial College London by investigating the acute and long-term effects of psilocybin on the brain (in healthy naïve subjects).

Fernando Rosas
Dr. Fernando E. Rosas is a Postdoctoral Researcher at Imperial College London, based at the Centre For Psychedelic Research.

David Erritzoe
David Erritzoe is the clinical director of the Centre for Psychedelic Research at Imperial College London. His work focuses on brain imaging (PET/(f)MRI).

Robin Carhart-Harris
Dr. Robin Carhart-Harris is the Founding Director of the Neuroscape Psychedelics Division at UCSF. Previously he led the Psychedelic group at Imperial College London.

Compound Details

The psychedelics given at which dose and how many times

Psilocybin 1 - 25
mg | 1x

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