Using large prospective online samples and an independent controlled trial, the authors show that psychedelic use shifts metaphysical beliefs away from physicalist/materialist views and towards panpsychism and fatalism, with changes detectable up to six months. These shifts correlated with greater past use and improved mental-health outcomes, were moderated by baseline impressionability and mediated by perceived emotional synchrony during the experience, implying a causal influence of psychedelics on metaphysical belief.
Are psychedelics able to induce lasting changes in metaphysical beliefs? While it is popularly believed that they can, this has never been systematically tested. Here we exploited a large sample derived from prospective online surveying to determine whether and how beliefs concerning the nature of reality, consciousness, and free-will, change after psychedelic use. Results revealed significant shifts away from ‘physicalist’ or ‘materialist’ views, and towards panpsychism and fatalism, post use. These changes remained detectable at 6 months, and were associated with the extent of past use and improved mental-health outcomes. Path modelling suggested that the belief-shifts were moderated by impressionability at baseline and mediated by perceived emotional synchrony with others during the psychedelic experience. The observed belief-shifts post psychedelic use were confirmed by data from an independent controlled clinical trial. Together, these findings imply that psychedelic use has a causal influence on metaphysical beliefs – shifting them away from ‘hard materialism’.
Metaphysics concerns fundamental questions about reality, consciousness and free will, and people typically hold distinct metaphysical positions even if not explicitly aware of them. Timmermann and colleagues note that intense life events and altered states — including psychedelic experiences — can make such beliefs explicit, and that psychedelic experiences often include features (mystical-type experiences, perceived encounters with supernatural entities, feelings of unity or cosmic consciousness) that could plausibly induce durable shifts in metaphysical outlooks. Prior evidence for such shifts has been largely anecdotal, qualitative or retrospective, and no systematic, controlled quantitative study had tested whether psychedelics alter metaphysical beliefs. This study set out to address three linked questions: whether psychedelic use can causally affect core metaphysical beliefs about reality, consciousness and free will; whether any belief changes relate to mental-health outcomes; and what psychological mechanisms underlie the putative changes. To do so, the researchers conducted a prospective survey of people planning to attend psychedelic ceremonial retreats, measuring beliefs before and after use, and sought external validation by analysing data from an independent double-blind randomised clinical trial comparing psilocybin therapy with a 6-week course of escitalopram in patients with major depressive disorder.
Papers cited by this study that are also in Blossom
Brouwer, A., Carhart-Harris, R. L. · Journal of Psychopharmacology (2020)
Barrett, F. S., Johnson, M. W., Griffiths, R. R. · Journal of Psychopharmacology (2015)
Davis, A. K., Clifton, J. M., Weaver, E. G. et al. · Journal of Psychopharmacology (2020)
Griffiths, R. R. · Journal of Psychopharmacology (2008)
The primary observational sample comprised respondents (866 at baseline) who planned to attend a ceremony involving a psychedelic (psilocybin/magic mushrooms/truffles, ayahuasca, DMT, San Pedro, LSD/1P-LSD). Recruitment was via online advertising and signup through psychedelicsurvey.com. Eligibility criteria are referred to but not fully reported in the extracted text. Assessments occurred at baseline (one week prior to the experience), and at 4 weeks and 6 months after the retreat. Two main outcome instruments were used: a self-constructed Metaphysical Beliefs Questionnaire (MBQ) and selected items from the Free Will and Fatalistic Determinism subscales of the FAD-Plus. Wellbeing was measured with the Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS). Baseline trait measures included absorption (MODTAS), peer conformity (four items from the short suggestibility scale), and identity fusion (a pictographic single-item measure of oneness with the group). For the controlled clinical trial, a shortened MBQ (five items mapping to Ontological Transcendentalism, Supernatural Transcendentalism, Dualism, Materialism, Non-naturalism) and the Universality subscale from the Spiritual Transcendence Scale were administered. An exploratory factor analysis of 13 MBQ items at baseline led the authors to select a unifactorial solution after heuristics and inspection; this principal factor was labelled Non-physicalist Beliefs (NPB). Items with positive loadings indexed beliefs in transcendental realms, panpsychism, dualism and non-natural unifying principles, while negatively loading items indexed hard materialism. The NPB factor showed good internal consistency (Cronbach's alpha = 0.86). Statistical approaches included paired t-tests (two-tailed, Bonferroni-corrected) to compare baseline versus follow-up beliefs, Cohen's d for paired effect sizes, chi-squared tests to assess conversion between categorical metaphysical positions, and Pearson correlations to relate belief changes to wellbeing. A longitudinal exploratory path analysis modelled predictors and mediators of change in NPB, with candidate predictors including demographics, trait absorption, baseline suggestibility measures, identity fusion, and acute experience measures: mystical-type experience (MEQ) and emotional synchrony (PESC); only PESC was retained due to nonsignificance of MEQ. For the controlled trial (psilocybin n=30, escitalopram n=29), changes in NPB between baseline and 6 weeks were compared using a repeated-measures ANCOVA adjusted for baseline, with post-hoc Wilcoxon tests (Bonferroni-corrected) and effect sizes reported. Single-sided p-values were used for controlled analyses where directional hypotheses were pre-specified.
Factor analysis of the MBQ yielded a single Non-physicalist Beliefs (NPB) factor that loaded positively on items referring to transcendental realms, a non-natural unifying principle, panpsychism and dualism, and negatively on items reflecting hard materialism; the factor demonstrated good internal consistency (alpha = 0.86). In the prospective retreat sample, paired analyses indicated significant shifts away from physicalist/materialist views and toward positions such as panpsychism, transcendentalism and fatalistic determinism after psychedelic use. Some individual-item changes remained significant at the 6-month follow-up. Correlationally, greater lifetime psychedelic use was associated with weaker materialist beliefs at baseline (r = 0.223, p < 0.0001) and with stronger baseline fatalistic determinism (r = 0.186, p < 0.0001). When respondents were classified by their strongest baseline metaphysical preference (materialist, dualist, idealist, or none/mixed), baseline hard-materialists were more likely than not to shift away from that position after psychedelic use, typically moving toward a none/mixed stance or toward hard-dualism. Conversely, 37% of baseline hard-dualists adopted a none/mixed position post-psychedelics. Respondents who were moderately inclined toward panpsychism tended to become stronger endorsers of that position after use. A longitudinal path analysis of the retreat data produced a well-fitting model linking trait and situational variables to NPB change. Trait-level susceptibility factors (absorption and peer conformity), lower age, female gender and pre-session identity fusion predicted higher emotional synchrony during the ceremony, and emotional synchrony (PESC) strongly mediated increases in NPB scores. The mystical-type measure (MEQ) was not retained in the final model due to nonsignificance. External validation from an independent double-blind randomised controlled trial showed convergent results. A significant drug-by-time interaction was observed (F(56) = 3.13, p = 0.041, one-tailed). Post-hoc testing found that the psilocybin group showed significant shifts away from hard materialism at 6 weeks (Z = 2.28, p = 0.02, d = 0.45), whereas the escitalopram group did not (Z = 0.24, p = 0.33, d = 0.2). Among treatment responders (≥50% reduction in depression scores), those in the psilocybin arm showed larger shifts in NPB than escitalopram responders (Z = 1.74, p = 0.041, Hedges' g = 0.56, 90% CI = [-0.17, 1.26]). Finally, changes in NPB in the psilocybin condition correlated with greater endorsement of a unifying spiritual principle as measured by the Universality subscale.
Timmermann and colleagues interpret their converging observational and controlled findings as supporting the inference that psychedelic use can causally influence metaphysical beliefs, shifting people away from hard physicalism and, in many cases, toward positions such as panpsychism, non-naturalism and certain forms of dualism or fatalism. The authors highlight several pieces of convergent evidence for causality: prospective pre–post measurement in a large sample, especially pronounced shifts among psychedelic-naïve participants, mediation by the quality of the acute experience (emotional synchrony), correlation between extent of past use and baseline beliefs, and replication in an independent randomised controlled trial. The path analysis suggested a plausible psychological mechanism in which trait-level susceptibility to social influence (absorption, peer conformity, identity fusion) interacts with state-level group emotional synchrony during the psychedelic ceremony to produce belief revisions. Demographic correlates such as younger age and female gender were also predictive of change. The authors situate these results within broader theorising about psychedelics increasing the plasticity of high-level beliefs (for example, the REBUS model) and note potential biological substrates, including serotonin 2A receptor–related plasticity. The investigators acknowledge important qualifications and uncertainties. They emphasise the role of contextual and cultural factors in shaping the direction of belief-change and note that some shifts represented a move away from extreme positions, whereas other beliefs (e.g., panpsychism) showed an increase in confidence among some participants. Ethical concerns are raised about the potential for suggestibility and context-dependent transmission of beliefs — particularly in collective settings such as retreats — and the authors call for further research on the bioethical and societal implications of psychedelic-induced belief change. They also caution against interpreting the observed association between non-physicalist belief shifts and improved wellbeing as evidence that any particular metaphysical stance is inherently beneficial, noting that non-physicalist beliefs can sometimes be maladaptive (for example, via avoidance or mistrust of scientific advice). Finally, the authors argue that greater research is needed on the societal, cultural and neurobiological aspects of psychedelic-related shifts in core beliefs, given the observed associations with mental-health outcomes and the increasing prevalence and potential scaling of psychedelic use. They conclude that their mixed-methods approach — combining prospective observational data with controlled trial replication — supports the claim that psychedelics can alter deeply held metaphysical beliefs and that these changes merit further scientific and ethical scrutiny.
Metaphysics is a branch of philosophy that studies themes such as the fundamental nature of reality, consciousness, and free will. Research has shown that most of us hold distinct metaphysical positions -even though we may not be aware of it. Metaphysical beliefs interface with such basic domains as health, religion, law, politics and education. They are closely entwined with a society's culture and its stability. Although often held implicitly, metaphysical beliefs can become explicitly manifest during or after particularly intense life experiences or altered states, such as near-death experiences, meditation, hypnosis, experiences of 'awe', traumatic events, and psychedelic drug-induced experiences. Focusing specifically on psychedelics, recent evidence has demonstrated that psychedelics can reliably and robustly induce intense, profound, and personally meaningful experiences that have been referred to as 'mystical-type', 'spiritual', 'religious', 'existential', 'transformative, or 'peak'. It is tempting to hypothesize that these experiences operate as key mediators of potentially enduring transformations in metaphysical beliefs. Some specific facets of these potentially transformative psychedelic experiences include: perceived encounters with 'supernatural' beings, transcendence of the presumed physical bounds and laws of this 'consensus reality', encounters with an 'ultimate reality', witnessing or comprehending spatial and temporal vastness, a perception that the 'cosmos is fundamentally conscious'and/or that all things are essentially inter-related or connected, i.e. the so-called 'unitive experience'. The unitive experience is arguably the most tangible feature of these experiences. It is closely related to the so-called 'overview effect', 'universal insight', experience of 'awe'and so-called 'non-dual' states. Such experiences appear to have a powerful capacity for mediating major shifts in perspective, including shifts in metaphysical beliefs. While some anecdotal, qualitative and retrospective reports hint that psychedelics can change metaphysical beliefs, and that these shifts in beliefs are often explained post-hoc as having been triggered by revelations or insights, there have been no formal, systematic, controlled and quantitative investigations of this phenomenon. Addressing this knowledge gap, the present study sought to address three key questions: 1) Can psychedelics causally affect core beliefs concerning the nature of reality, consciousness and free will? 2) What is the relationship between the putative belief-changes and mental health? 3) What are the psychological mechanisms underlying the putative belief-shifts? For this purpose, we developed a prospective survey requiring respondents answer questions pertaining to a range of metaphysical beliefs before and after attending a ceremonial retreat in which a psychedelic compound was taken. The external validity of these findings was subsequently examined via comparison with data derived from a randomized, controlled clinical trial in major depressive disorder, in which changes in beliefs were measured following psilocybin-therapy vs. a 6-week course of the selective-serotonin-reuptake-inhibitor, escitalopram.
866 respondents completed baseline surveys enquiring about their metaphysical beliefs (see Supplementary Results and Supplementary Tablefor sample characteristics). Items were formulated in a way to approximate classic metaphysical positions in non-specialist terms, and therefore do not necessarily measure precise philosophical positions, but rather folk beliefs associated with them. A factor analysis on the new belief items developed for the survey (together with 3 items derived from previous research) revealed a single belief factor comprised of 9 items, which we have labelled Non-physicalist Beliefs (NPB; see Methods for factor analysis results). This single factor showed good internal consistency (Cronbach's alpha = 0.86), and included positive loadings (>.4) for items related to beliefs in separate and supernatural realms of existence, a non-natural unifying principle in reality, panpsychism, dualism, and solipsism/idealism. Items that loaded negatively (<-0.4) referred to 'hard' monistic materialist or physicalist positions, or a belief in natural (as opposed to super-natural) explanations for phenomena in the universe (naturalism). These items and their loadings are shown in Table(See Supplementary Tablefor the full Metaphysical Beliefs Questionnaire).
Factor loading There exists another separate realm or dimension beyond this physical world that can be experienced and visited. (Ontological transcendentalism)
Visiting such immersive "realms" or "worlds" can sometimes depend on a supernatural / magical transition process or event. (Supernatural transcendentalism)
The universe obeys a unifying principle which is beyond any possible material or scientific explanation. (Non-naturalism) 0.776 There is just one primary reality: the physical; the mind (and/or consciousness) is just physical/functional properties of the brain and has an entirely material explanation.). Analyses of each individual item for the NPB factor revealed increases in notions of transcendentalism, mind-body dualism, and panpsychism -among others, with some changes remaining significant for 6 months (see Figure-left and Supplementary Figurefor findings for 'naïve' respondents). Additionally, a significant positive correlation was found between previous psychedelic use and shifts away from the hard-materialism pole of the hard-materialism vs. hard-dualism spectrum (Figure-right) at baseline (r = 0.223, p <0.0001).). Consistent with the results described above, correlational analysis revealed a mild (r = 0.186) but significant positive correlation (p < 0.0001) between baseline beliefs in Fatalistic Determinism and lifetime psychedelic-use (Supplementary Figureand see Supplementary Figurefor correlations between scales at different timepoints).
To further explore the relationship between psychedelic use and shifts in participant's metaphysical positions, we separated the sample into 4 groups corresponding to which metaphysical position participants mostly strongly endorsed at baseline. Respondents with either no positive endorsement or scoring equally high on more than one item were grouped under the label 'none/mixed', otherwise they were categorised as either: dualists, idealists or materialists. Results showed baseline 'hard-materialists' tended to shift away from this position after psychedelic use. In fact, such shifts were more common than not. We also found that among those who did shift, the nature of this shift was either towards the 'none/mixed' position or 'hard-dualism'. Intriguingly, shifts away from polar metaphysical views was also evident for a large portion (37%) of baseline 'hard-dualists' who tended to reject any preference or endorse an equanimous (i.e. mixed) position postpsychedelics (Figureand Figure). Separately, however, we observed that those who held more moderate views on 'panpsychism' became more convinced of this position post-psychedelics (labelled 'believers') (Figureand Figure). These prospective findings were matched by correlations between lifetime psychedelic use and stronger panpsychist and weaker materialist views, at baseline. (Figure).
A path analysis was performed to examine mechanisms associated with shifts in the relevant non-physicalist beliefs (see Methods for details). Included in the model were items and scales pertaining to the acute subjective effects of psychedelics as well as environmental and social-contextual variables relevant to the retreat experience. Results supported a model with excellent fit (Supplementary Table
To test the validity and replicability of our findings, we administered items corresponding to the NPB during a double-blind randomized-controlled trial comparing a group (n=30) receiving psilocybin therapy with another undergoing a 6week course of escitalopram (n=29) (See Methods for details of trial design). Results replicated well across the independent studies. That is, a significant drug versus time (before treatment and 6 weeks after) interaction was observed (F(56) = 3.13, p = 0.041, one-tailed). Post-hoc tests revel that shifts away from hard materialism were evident in the psilocybin group only (Z = 2.28, p = 0.02, d = 0.45). The escitalopram group showed no changes in NPB (Z = 0.24, p = 0.33, d = 0.2). (Figure). Importantly, consistent with the above-reported findings of a relationship between belief shifts and positive mental health outcomes, significantly greater shifts away from hard materialistic beliefs (the NPB factor) were found for those patients who showed a clinically meaningful response (defined as at least 50% reduction in depression scores from baseline to week 6) only to psilocybin, as opposed to escitalopram (Z = 1.74, p = 0.041, g = 0.56, 90% CI = [-0.17, 1.26]) (Figure). Finally, we found that the belief shifts in the psilocybin condition were largely correlated with positive endorsement of a unifying spiritual principle (see Supplementary Methods for the items used), indicating that changes in metaphysical beliefs are related to spiritual beliefs (Figure).
The present study sought to test the hypothesis that psychedelic experiences mediate changes in metaphysical beliefs concerning the nature of reality, prospective/observational and smaller-sample but well-controlled research findings converged, implying that psychedelic-use may indeed be a casual determinant of the relevant shifts in metaphysical beliefs. Furthermore, the belief-shifts were correlated with positive mental health changes; namely, improvements in well-being in the observational data and depression scores in the controlled research data. Path analyses on the psychedelic retreat-derived observational data highlighted the predictive relevance of certain psychological traits, including 'absorption' -which indexes differential proclivity to states of immersion, absorption, hyper-focus or flow, and peer conformity. Trait absorption has been found to predict propensity for spiritual-type experiencesand be related to trait suggestibility-as well as a serotonin 2A receptor genetic polymorphism-the key receptor target for classic psychedelics. Peer conformity has also been found to relate to suggestibility. Regarding demographic variables, age and gender were other relevant predictors of belief shifts: specifically, lower age and female gender were predictive of the relevant changes. The relationship between lower age and suggestibility is well established. Pre-state identity fusion (feelings of identification with the retreat group) was another relevant variable moderating susceptibility to the relevant belief-shifts. All of these variables moderated 'emotional synchrony'felt during the psychedelic ceremony itself. Higher emotional synchrony scores strongly mediated the relevant shifts in metaphysical beliefs, i.e., away from physicalism. Taken together, these results imply an interaction between trait-level susceptibility to social influence and state-level group emotional alignment, 'attunement' or synchrony under the psychedelic, as a plausible mechanism for driving metaphysical belief-shifts. The role of differential susceptibility to environment bears relevance to popular models of individual differences in susceptibility to psychopathology, including those that make specific reference to genetic differences in serotonergic functioning. Findings of increased (state) suggestibility under serotonergic psychedelics are interesting in this context. The role of prior expectancy and acute suggestibility in moderating and mediating changes in mental health outcomes post psychedelic use is an area deserving more research. The present study's path modelling results may bear relevance to our understanding of the mechanisms underpinning other robust and often enduring psychological changes associated with psychedelic use, such as personality shifts, improvements in mental health outcomes, plus changes in ecological, politicalspiritualand religious positions. These findings also add further weight to the principle that outcomes of psychedelic use strongly depend on contextual variables. They also mesh well with work suggesting that ritual can enhance cultural transmission, and it is logical to surmise that this effect could be further enhanced via the pro-suggestibility action of psychedelics. Advancing our understanding of the biological aspect of these psychological mechanisms associated with changes in beliefs is a research area deserving special focus. For example, the relationship between serotonin 2A receptor agonism-induced cortical plasticity seems likely to be highly relevant in this regard. A recent predictive coding inspired model of the brain action of psychedelics, known as 'REBUS' (RElaxed Beliefs Under pSychedelics), may provide some useful inspiration for aiding investigations of the neurobiology of belief change processes. The REBUS model proposes that rendering high-level beliefs and assumptions more plastic under psychedelics is a key mechanism underlying their acute phenomenological and potential therapeutic effects. Like previous work in other psychological domains (discussed above), our results indicate that changes in beliefs tend to occur in a particular direction (i.e., in the present case, away from physicalism). At the aggregate level, the dominant direction of this shift points away from 'hard' metaphysical views, and away from 'hard materialism' in particular. However, results also reveal signs of a 'hardening' (or increase in confidence) in beliefs in panpsychism and related domains of 'hard' dualism. More work is needed to address the question of whether the apparent directional nature of postpsychedelic belief-shifts are entirely context dependent, or whether there may also be a context-independent component to the changes. Indeed, it may transpire that these possibilities are not mutually exclusive, e.g., acute belief relaxation may be somewhat context independent but sub-acute belief revision is more dependent on context. This matter is related to the question of whether or not psychedelics are intrinsically 'healing'. The role of contextual influences on post psychedelic belief-shifts, plus differential susceptibility to these, is an important topic to examine further, particularly given the present evidence indicating a significant role for social-psychological influences on key long-term outcomes. If, for example, the direction and nature of psychedelicinitiated belief changes depends entirely on contextual factorsand differential susceptibility to these, then this raises important bioethical implications, invoking, in the extreme, notions of 'mind-control' and 'brain-washing'. These matters may be particularly relevant in relation to collective psychedelic experiences such as often occur at psychedelic retreats, in which the exchange of ideas, beliefs and worldviews are commonplace, and often centrally promoted. However, note that belief-shifts in a consistent direction were also observed in the clinical trial data reported here, in which there was no conscious, intentional priming toward any particular metaphysical position. Nonetheless, it is important to note that even in therapeutic and research environments, the psychedelic experience and surrounding process will be imbued with cultural factors that could easily influence beliefs in a particular direction. Accounts of the apparent modulation of core beliefs via psychedelic drug use appears to be consistent across different Western cultures, and the types of beliefs that participants appear to gravitate towards after psychedelic use are somewhat consistent with those that are culturally held by many indigenous and mestizo populations, as well as some "New Age" groups, particularly if they have connections with psychedelic drug use. One could interpret these observations as consistent with a context-independent belief shift, or alternatively, evidence of a bidirectional causal relationship between cultural values and psychedelic use, e.g., that certain cultures and viewpoints lend themselves toward psychedelic use, or even psychedelic research. Assessing the value of competing philosophical positions is beyond the remit of the present work -, and, some might argue, beyond the remit of science. However, we acknowledge that this matter has important ethical, social and psychological implications and therefore merits some further comment. Thus, one pragmatic way in which science could approach this issue would be to assess how different metaphysical positions interface with individual (mental) health, as well as other indices of individual plus group or societal health, e.g., population-level well-being. The present study found a positive association between changes in metaphysical beliefs away from physicalism and increased psychological well-being. Moreover, this finding was replicated in independent data from controlled research where beliefshifts in a consistent direction were found in responders (vs. non-responders) to psilocybin-therapy for depression, and no such relationship was evident for an active-treatment (selective serotonin reuptake inhibitor, antidepressant, 'escitalopram') control arm, even in those who responded to that intervention. It would be hasty, in our view, to interpret these findings as evidence in favour of the positive value of e.g., anti-materialist, pro-panpsychist or fatalistic beliefs. For example, the adoption of non-physicalist or supernatural beliefs have been associated with maladaptive coping strategies such as avoidance or escapism, e.g. via 'spiritual bypassing'. Furthermore, mistrust of scientifically-informed advice can foment problematic collective behaviours -such as a rejection of strategies for the prevention of COVID-19 transmission. These issues may speak to the dangers of both an open-mindedness 'overshoot', and 'undershoot', with the former associated with paranoid, conspiratorial and escapist thinking and the latter, a potential cognitive fusion or rigidity linked to poor psychological well-being. Again, however, these different presentations may not be mutually exclusive, e.g., some people may oscillate between them. The principle that psychedelic experiences can mediate fundamental and enduring shifts in belief has important bioethical implications. One popular historical narrative is that spiralling psychedelic use in 1960s catalysed counter-cultural views and activities that provoked prohibitionist policies which effectively suspended research and clinical/therapeutic work with these compounds. Recent evidence suggests that psychedelic use has increased exponentially in the last decade in the USand is set to scale-up further due to increasing public interestand liberalising policies on access. Greater research is therefore clearly needed on the societal implications of putative psychedelic-induced belief-shifts. Seefor relevant discussions. A major advance of the present work is its synthesis of converging lines of evidence in support of a causal role for psychedelic use on the relevant belief changes. These lines of evidence include: 1) that the belief-shifts were observed prospectively (i.e. before vs after psychedelic use) in a large sample, 2) especially pronounced shifts were seen in psychedelic-naïve participants, 3) the quality of the acute experience (i.e., emotional synchrony) was found to be a significant mediator of the belief-shifts, 4) extent of past psychedelic use correlated with beliefs in the predicted direction, and 5) independent data from a separate controlled study in a distinct population, replicated findings from our observational data. It is also relevant that previous controlled studies have demonstrated post-psychedelic changes in other psychological domains after controlling for potential confounding factors. To conclude, this mixed method study, comprising of an observational plus controlled research design, has comprehensively assessed the relationship between psychedelic drug use and metaphysical beliefs. Findings converged on the inference that psychedelic use inclines individuals away from hard physicalist beliefs and towards dualistic, panpsychist, and fatalistic beliefs, thus highlighting the potential of psychedelics to alter some of the most deep-seated and influential human beliefs. These results have profound scientific, societal, political and philosophical implications, and therefore demand further investigation.
Respondents planning to attend a ceremony involving a psychedelic substance (psilocybin/magic mushrooms/truffles, ayahuasca, DMT, San Pedro, LSD/1P-LSD) were recruited via online advertisements and invited to sign up for the study via the website www.psychedelicsurvey.com. Eligibility criteria to participate consisted in:
There were two main outcome measures in this study which were employed at baseline (one week prior to the experience), 4 weeks, and 6 months after attending the retreat. They were (1) a self-constructed Metaphysical Beliefs Questionnaire (MBQ; see Supplementary Table), and (2) items extracted from the Free Will and Fatalistic Determinism subscales (containing 9 items in total) of the FAD-Plus can strongly predict the character of psychedelic experiences) and the subscale peer conformity from the Multidimensional Iowa Suggestibility Scale(suggestibility is known to be sensitive to psychedelic administration 51 ) were both measured at baseline. Finally, identity fusion (the visceral experience of 'oneness' with the group) was measured shortly before the session as a single pictographic item. We also explored the extent to which any changes in beliefs might be associated with changes in psychological well-being. Well-being was measured at baseline, 4 weeks after, and 6 months after the ceremony using the Warwick-Edinburgh Mental Wellbeing Scale, which has been shown to be sensitive to the effects of psychedelics. For controlled research, a shortened version of the Metaphysical Beliefs Questionnaire was used (containing the following items: Ontological Transcendentalism, Supernatural Transcendentalism, Dualism, Materialism, and Non-naturalism), from which the NPB factor was extracted. Also, for the controlled study, the 'Universality' subscale from the Spiritual Transcendence Scale(see Supplementary Methods for the items) was used to determine the association between changes in beliefs and changes in spirituality.
An exploratory factor analysis was performed on the Metaphysical Beliefs Questionnaire (see Supplementary Tablefor all items) at baseline. Multiple heuristics were used to determine the optimal number of factors to retain among the 13 items included in the analysis. Parallel analysis, optimal coordinate and the 'Kaiser rule', suggested a three-factorial solution, whereas acceleration factor and visual examination of the scree plot a unifactorial solution (Supplementary Figure). Examination of factor loadings showed that in the three-factorial solution, only one and two items loaded on factors two and three, respectively. Thus, a unifactorial solution was chosen, with standardized loadings presented in table. After removal of items with a. factor loading <.4. Finally, Cronbach's alpha was used to determine internal consistency. Analyses were conducted to determine changes in beliefs (baseline vs 4 week post ceremony, and baseline vs 6 months post ceremony) for all respondents. Separate analyses were performed using responses from participants with no previous psychedelic experiences, on the grounds that respondents with previous psychedelic experiences might already have had shifts in the relevant beliefs. Paired t-tests were performed to assess the statistical significance of changes in specific beliefs (the principal factor extracted from the MBQ and the Free-Will and Fatalistic Determinism subscales from the FAD scale). Two-tailed and Bonferroni-corrected pvalues are reported. Cohen's d effect sizes are reported for all paired analyses. Following previous studies, we also performed analyses to determine the rate of conversion from baseline 'hard' metaphysical positions regarding materialism, idealism and dualism. In order to do this, we divided the groups based on their tendency to endorse materialism, dualism, idealism or 'none/mixed' based on their initial Likert responses for items 3, 4 and 5 of the MBQ (see Supplementary Table). The single highest score between the 3 items corresponded to the group each respondent would be allocated. If there were competing highest scores, or if the highest score was below or equal to a neutral score, then subjects were grouped as Agnostics. Determining the rate of conversion from a hard metaphysical position was done via Chi-squared tests comparing percentages of 'Remainers' (those respondents who did not show any change according in groups for subsequent timepoints) and 'Converted' (those who did in any direction). Determining differences between the groups toward which Materialists respondents converted (the only group showing a significant rate of conversion) was also done by performing paired Chi-squared tests for each pair of comparisons (p values were Bonferroni-corrected for multiple comparisons). We also performed a similar procedure using a single item corresponding to panpsychism from the MBQ, by classifying subjects as 'Believers', 'Sceptics' and 'Neutral' according to scores above, below or corresponding to, the neutral Likert score. Chi-Squared tests were performed for comparing Conversion from and towards a different metaphysical position. A longitudinal exploratory path analysis was performed to determine the psychological mechanisms associated with changes in NPB. Included were items and scales pertaining to the acute subjective effects of the psychedelic as well as environmental and social contextual variables relevant to the retreat experience. Specifically, the intensity of mystical-type (MEQ) and emotional synchrony experiences (PESC), measured on the day post-session, were expected to predict baseline-corrected NPB scores 4 weeks post-session, although due to nonsignificance of effects, only the PESC was retained in the model. In the case of collective emotional synchrony experiences, this effect was expected to be moderated by peer conformity measured at baseline, calculated as the sum of the 4 peer conformity-items from the short suggestibility scale (SSS). Demographic variables, trait absorption (MODTAS), baseline supernatural NPB, and alignment with the group assessed hours before the session via a pictographic identity fusion scalewere included in the model as predictors of acute experience (MEQ and PESC) scores. Whenever a respondent attended more than one psychedelic ceremony and provided multiple reports, only the largest score for each of these scales was considered. The association between changes in NPB and mental health outcomes was assessed by Pearson-Point correlational analyses between changes in the NPB factor and changes in wellbeing (changes in WEBMWS scores). For the controlled research analysis, changes in NPB between baseline and the 6-weeks timepoint was compared between the psilocybin and escitalopram groups using a repeated measures ANCOVA, adjusted for baseline. Post-hoc tests comparing baseline and 6-weeks post-treatment were performed using Wilcoxon signed rank test for dependent samples (Bonferroni-corrected). Changes in NPB Beliefs were compared for psilocybin versus escitalopram remitters using Wilcoxon rank sum test for independent samples. Finally, the association between Changes in NPB and changes in Spiritual Beliefs were assessed using the Universality subscale from the Spiritual Transcendence Scale. Single-sided p-values are reported for controlled research analysis as clear hypotheses were derived from the main survey data presented here. Cohen's d and Hedges' g effect sizes are reported for paired and independent tests, respectively.
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