The phenomenology of psilocybin's experience mediates subsequent persistent psychological effects independently of sex, previous experience, or setting

Psilocybin, a serotonergic tryptamine psychedelic, has accumulating evidence for rapid antidepressant and enduring positive effects on well-being and attitudes in healthy and clinical populations. A central question addressed in recent research is the extent to which the subjective psychedelic experience — particularly peak or mystical-type states and features such as ego dissolution — mediates longer-term psychological benefits. At the same time, uncertainty remains about whether factors such as previous psychedelic experience, repeated dosing, sex, and the specific testing environment (for example EEG versus fMRI settings) influence either the acute phenomenology or the persistent outcomes. This study set out to test whether the acute phenomenological features of a psilocybin session predict persistent changes in mood, well-being and spirituality in healthy volunteers, while accounting for previous psychedelic experience, repeated administration, sex, and experimental setting. Tylš and colleagues used validated instruments for acute states (the Altered States of Consciousness scales, ASCs, and a time-course Visual Analogue Scale, VAS) and for persisting outcomes (the Persisting Effects Questionnaire, PEQ) to examine these relationships in a controlled, double-blind, placebo-controlled, crossover design embedded within a larger neuroimaging project. The investigators hypothesised that characteristics of the acute experience would drive long-term positive outcomes and treated the other variables as exploratory moderators.

The study employed a double-blind, placebo-controlled, crossover design with two consecutive neuroimaging arms: an EEG-focused arm followed by an fMRI (or simultaneous EEG/fMRI) arm. Each participant received both psilocybin and placebo in each arm, resulting in up to four dosing sessions per person. The order of administration was balanced across participants and the minimum interval between sessions was 28 days. Recruitment used peer-to-peer snowball sampling and the protocol included preparatory sessions, continuous sitter support (one man and one woman, one a psychiatrist), and clinical/biological screening before each dose. Forty participants were enrolled; additional demographic detail is referenced to figures in the original text and is not fully reported in the extracted prose. Oral psilocybin was administered at 0.26 mg/kg (capsules adjusted from 1 and 5 mg units), with average reported absolute doses of about 18.6 mg (range 15–24 mg) noted in the extract. Dosing sessions lasted about 6–8 hours, typically beginning early morning, and included blood sampling via an intravenous cannula at baseline and 1, 2, 3 and 6 hours post-dose for psilocin serum level measurement. During the study the assay laboratory and technique changed for some participants (GC-MS for earlier subjects, LC-MS for later subjects). Acute subjective effects were measured immediately post-session using the 72-item ASCs, which yields subscales Oceanic Boundlessness (OBN), Dread of Ego Dissolution (DED), Visionary Restructuralization (VRS) and an overall GASC score. Participants also plotted a continuous 7-hour VAS trace of pleasant/unpleasant emotional valence, which was digitised and summarised as AUC and a positive-only pAUC; from these the Relative Index of Positive Experience (RIPE = pAUC/AUC) was derived and used to classify participants (pleasant-only vs oscillating). Persistent effects were assessed 28 days after dosing using the 140-item PEQ comprising positive and negative subscales across attitudes about self and life, mood, social effects, behaviour and spirituality, plus three global meaning/spirituality/well-being items. Statistical analysis included visual and Shapiro-Wilk tests for normality, paired t-tests comparing psilocybin and placebo (with Benjamini-Hochberg correction applied to some comparisons), and repeated-measures ANOVA models for each dependent variable (DED, OBN, VRS, GASC, and PEQ positive subscales). The ANOVAs controlled for previous psychedelic experience, occupation (mental-health specialist or not), order of administration, and sex; the repeated structure used participant ID with Session (EEG/fMRI) and Substance as within-subject factors. Pearson correlations between ASCs and PEQ subscales were calculated (BH correction applied where specified). Several exploratory analyses were reported with uncorrected p-values, including comparisons by RIPE group and correlations using the peak and end VAS scores (the peak–end rule). Definitions and thresholds for non-responders and placebo responders were also specified for supplementary analyses.

Psilocybin produced clear acute subjective effects on the ASCs compared with placebo. Student's t-tests and repeated-measures ANOVAs showed significant treatment effects across all ASCs subscales (OBN, VRS, DED) and the GASC in both the EEG and fMRI arms (reported p < 0.001 for subscale comparisons). Across models the investigators did not detect significant main effects of sex, previous psychedelic experience, occupation, or a Treatment:Session interaction (EEG versus fMRI) on ASCs scores. On the PEQ, psilocybin elicited significantly greater positive persisting effects than placebo across all positive subscales (ANOVA and paired tests, reported p < 0.001 with adjustment). No significant effects of previous experience, sex, occupation, administration order, or first-versus-second psilocybin session were found on PEQ positive scores. In the sample, 13 out of 39 participants (33%) rated a psilocybin session among the top five most meaningful experiences of their lives; additional proportions were reported for spiritual significance and perceived improvement in well-being. Correlational analyses linked acute phenomenology and persisting outcomes. In the EEG arm, OBN, VRS and GASC were positively correlated with nearly all positive PEQ subscales, and most of these correlations survived correction for multiple comparisons. DED also showed positive correlations with PEQ in some analyses, contrary to expectations, though in the fMRI arm correlations were weaker and none survived correction. Exploratory RIPE analyses divided participants by the proportion of positive versus mixed-valence experience (threshold 0.98). In the EEG arm those who oscillated between pleasant and unpleasant emotions had higher DED and GASC scores but also greater long-term positive changes (attitudes about self, behaviour, and mood); this pattern was not replicated in the fMRI arm (analyses reported without multiple-comparison correction). Time-course analyses using peak and end VAS values showed mild positive correlations with some PEQ subscales (uncorrected). Additional observations concerned heterogeneity in acute responsiveness: five participants were classified as non-responders to psilocybin by ASCs criteria, and four participants were classified as placebo responders; in some cases these patterns co-occurred with differences in measured psilocin serum levels. One non-responder had notably low serum psilocin. The investigators noted that most sessions concluded with participants in a neutral or positive mood; only one session was characterised as unpleasant throughout, and only three individuals ended with marginally negative mood states. No serious adverse outcomes were reported in the extracted results.

Tylš and colleagues interpret their findings as evidence that the intensity and phenomenology of the psilocybin experience at 0.26 mg/kg are moderately strong drivers of positive, persistent psychological effects in healthy volunteers. They highlight that OBN and VRS were consistently associated with lasting positive outcomes and that, unexpectedly, DED (the more challenging, anxiety-related dimension) also correlated positively with persisting benefits in several analyses. The authors suggest that this may reflect the dynamic nature of sessions, where DED-like moments can alternate with positive experiences; VAS-derived temporal data supported the presence of oscillating emotional trajectories for many participants. The investigators report no detectable influence of sex, prior psychedelic experience, or repeated exposure on either acute or persisting outcomes, noting that women in the sample received slightly lower absolute doses by virtue of body-weight adjustment but still achieved comparable subjective intensities. They also discuss setting-related effects: correlations between acute and persisting measures were stronger in the EEG arm than the fMRI arm, possibly reflecting carry-over or contextual influences given that all participants completed EEG first. The fMRI environment is noted as more demanding and potentially disruptive to uninterrupted subjective experience, which may have attenuated some associations. Key limitations acknowledged include challenges in maintaining blinding in psychedelic trials, reduced statistical power in the fMRI arm due to participant withdrawal, and the small sample size that increases vulnerability to influence from non-responders and placebo responders. The authors note methodological constraints such as changes in the laboratory assay for psilocin and incomplete control over pre-session factors (for example food intake) that might affect pharmacokinetics. They emphasise that many exploratory analyses presented uncorrected p-values and that the study was not powered for some subgroup comparisons. In terms of implications, the authors conclude that controlled psilocybin sessions can produce enduring positive changes in attitudes, mood and spirituality among healthy individuals and that challenging or anxiety-laden moments do not necessarily predict adverse long-term outcomes in a supported setting; indeed, such moments may be integral to therapeutic benefit. They suggest these results support the feasibility of repeated psilocybin administrations in clinical contexts and call for larger trials that can prospectively address non-responders, placebo/nocebo phenomena, and setting effects more robustly.

This study concludes that repeated, controlled administrations of psilocybin in healthy volunteers produce sustained positive changes in well-being, attitudes about self and life, and spiritual significance, and that these effects persist following a second exposure separated by an extended inter-dosing interval. Moments of anxiety or ego-dissolution appear not to preclude positive long-term outcomes when sessions occur in a supportive environment; instead, the overall intensity and the phenomenological profile of the acute experience — including peak and end-state characteristics — are linked to the magnitude of persisting benefits. The authors recommend that future clinical trials consider mechanisms to identify and study non-responders and placebo/nocebo responders and to optimise set and setting to support integration of challenging experiences.