Psychedelics alter metaphysical beliefs

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.

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.