Characterization and prediction of acute and sustained response to psychedelic psilocybin in a mindfulness group retreat

The study used a double-blind, placebo-controlled, between-subject design embedded within two iterations of a 5-day silent mindfulness retreat (sesshin). Forty participants were randomised to receive either psilocybin or inert placebo in matched groups; one participant withdrew after matching procedures leaving 39 completers, all described as expert Buddhist meditation practitioners. Eligibility screening included medical, psychiatric, urine drug and pregnancy testing; further screening details and selection criteria are reported in the Supplemental Information (not reproduced here). Psilocybin was administered orally as 315 μg/kg body weight (mean absolute dose ≈21.8 ± 3.8 mg); placebo was lactose in identical capsules. Administration occurred on day 4 at 10:30 in a highly structured retreat context that emphasised silence, individual practice, and guidance from an experienced Zen teacher. The retreat schedule comprised a 15-hour daily programme including sitting meditation, walking meditation, mindful work and meals; the intervention period was conceptually divided into preparation (days 1–3), drug/placebo day (day 4), and integration (day 5). Trait mindfulness was assessed the day before and the day after the retreat; state mindfulness and meditation depth were assessed each evening of the retreat; altered states and mystical-type experiences were assessed 360 minutes after drug administration; perceived changes in attitudes and behaviour were assessed at a 4-month follow-up, with both self-report and third-person (significant-other) versions. Primary instruments included the Toronto Mindfulness Scale (TMS) for state mindfulness, the Meditation Depth Questionnaire (MEDEQ) for meditation depth, the Freiburg Mindfulness Inventory (FMI, short form) for trait mindfulness, the 5D-ASC for altered states of consciousness (global score, five original scales and 11 subscales), the Mysticism Scale (M-scale) for mystical-type experience (three core dimensions and sub-dimensions), and the Life Changes Inventory–Revised (LCI-R) for long-term changes in nine clusters of attitudes/behaviours. Baseline measures included personality (NEO-FFI), absorption (Tellegen Absorption Scale), dispositional optimism (LOT-R), emotion regulation strategies (ERQ), lifetime mystical experiences, life satisfaction and symptom checklist. Statistical analysis employed repeated-measures ANOVAs for group × time/dimension effects, Pearson correlations for relations between scales, and backward-removal multiple regression to identify predictors of acute effects and follow-up changes. When ANOVAs indicated significance, Tukey's HSD-adjusted post-hoc tests were used; significance threshold was p < 0.05.

State mindfulness (TMS) increased across the 5-day retreat overall, but there was no significant group × time interaction and no main effect of drug: total TMS showed a main effect of time (F(4,148) = 4.41, p < 0.01) and increased from day 1 to day 5, while psilocybin did not significantly augment TMS relative to placebo. By contrast, meditation depth (MEDEQ) showed a significant group × time interaction (F(4,148) = 4.69, p < 0.001); post-hoc tests indicated a greater acute increase on day 4 in the psilocybin group than in the placebo group, and MEDEQ increased from day 1 to day 5 overall (F(4,148) = 14.44, p < 0.00001). Trait mindfulness (FMI) measured pre- and post-retreat increased overall and showed a significant group × time interaction (F(1,37) = 4.14, p < 0.05). FMI rose from pre-retreat to post-retreat (main effect of time F(1,37) = 22.85, p < 0.0001), and post-retreat FMI was higher in the psilocybin group than in the placebo group (post-hoc p < 0.001). Acute subjective effects measured 360 min after dosing showed large differences between groups. On the 5D-ASC, a significant interaction between group and main scales was observed (ANOVA F(4,148) = 36.27, p < 0.00001). Post-hoc comparisons indicated higher Oceanic Boundlessness (OB; p < 0.0001), Visual Restructuralization (VR; p < 0.0001), and Vigilance Reduction (VIR; p < 0.05) in the psilocybin group, while Anxious Ego Dissolution (AED) and Auditory Alterations did not differ between groups. Subscale analyses showed higher OB-related subscales (unity, spiritual experience, blissfulness, insightfulness, disembodiment) and VR-related subscales (complex and elementary imagery, audiovisual synesthesia, changed meaning of percepts) in the psilocybin group (all p < 0.01), with no group differences on AED-related subscales of impaired control, cognition and anxiety (p > 0.9). On the M-scale, there was a group × dimension interaction (F(2,74) = 14.81, p < 0.00001); extrovertive mysticism, introvertive mysticism and interpretation scores were all higher in the psilocybin group (all p < 0.01). Comparing acute retreat M-scale scores to each participant's lifetime strongest mystical experience yielded a significant group × time interaction (F(1,37) = 68.04, p < 0.00001); 19 of 20 participants (95%) in the psilocybin group met the a priori threshold for a “strong” mystical experience (≥60% scale maximum) versus 3 of 19 (16%) in the placebo group. Correlation analyses showed the OB dimension of the 5D-ASC correlated with all three M-scale dimensions (extrovertive r = 0.47; introvertive r = 0.59; interpretation r = 0.59; all p < 0.01). Multiple regression identified psilocybin intake as the largest single predictor across acute outcomes, accounting for η2 ranging approximately from 0.35 to 0.74. Optimism and openness accounted for significant proportions of variance in OB, VR and mysticism dimensions (optimism η2 = 0.16–0.25; openness η2 = 0.12–0.18). Emotion regulation by reappraisal was negatively associated with AED (p < 0.0001, η2 = 0.21); non-judgemental acceptance predicted higher introvertive mysticism (p < 0.05, η2 = 0.14) and interpretation (p < 0.05, η2 = 0.16). Meditation depth on the day before drug intake significantly predicted OB (p < 0.0001, η2 = 0.38) and interpretation (p < 0.05, η2 = 0.13). At the 4-month follow-up, self-reported changes on the LCI-R were greater in the psilocybin group (mean ± SEM 0.75 ± 0.09) than in the placebo group (0.19 ± 0.05), with F(1,37) = 23.41, p < 0.0001. Psilocybin participants reported larger increases on subscales for appreciation of life, self-acceptance, quest for meaning/sense of purpose, and appreciation of death (all p < 0.01), with trends on concern for others and spirituality and reduced concern with worldly achievements (p values ≈ 0.05–0.07). Third-person ratings from significant others (n = 37) showed a similar but attenuated pattern, with higher scores for self-acceptance and quest for meaning in the psilocybin group (all p < 0.01). Regression of follow-up change indicated that psilocybin intake (p < 0.05, η2 = 0.15) and loss of ego boundaries (p < 0.01, η2 = 0.20) predicted total LCI-R score; specific subdimensions (sacredness, ineffability, unity) accounted for variance in appreciation of life, quest for meaning, and self-acceptance (η2 up to 0.48 for sacredness predicting appreciation of life). Safety data reported no serious adverse events. Two participants reported transient emotional overwhelm during the peak drug effect but did not appraise it negatively. No persistent negative effects were reported at 4 months. Anxiety ratings on the 5D-ASC were low (mean 3%; range 0–10%).

Smigielski and colleagues interpret the findings as evidence that a single high but controlled dose of psilocybin given in the context of an intensive mindfulness retreat can deepen meditative states and occasion pronounced, positively valenced self-dissolution without concomitant anxiety or major loss of cognitive control in experienced meditators. Meditation depth increased across the retreat and showed an acute enhancement on the psilocybin day, while trait mindfulness measured 24 hours after the retreat was higher in the psilocybin group, a pattern the authors relate to prior findings with ayahuasca and to putative neuroplasticity-linked changes in mindfulness capacity. The study team emphasises that the combination of psilocybin and meditation produced substantially higher scores on spiritual experience, blissfulness and unity than meditation alone and produced these effects at higher rates than would be expected from meditation in isolation. They argue that mindfulness-related skills and the retreat setting (supportive group context, silence, structure) likely fostered positive experiential quality and buffered anxiety and vigilant deficits commonly seen with psychedelics. Regression analyses supported the importance of dispositional factors: openness and optimism predicted greater OB and mysticism scores, reappraisal reduced anxious ego dissolution, and pre-intervention meditation depth predicted positive dimensions of self-dissolution. With respect to lasting outcomes, the authors report greater self-rated and corroborated changes in appreciation of life, self-acceptance, search for meaning and attitudes toward death at 4 months in the psilocybin group, and they link these enduring changes to the intensity of acute self-dissolution, sacredness and ineffability—features previously implicated in sustained therapeutic benefits. The authors highlight consistency with other reports of long-term positive change after one or two doses of psilocybin. Key limitations noted by the investigators include the methodological challenge of blinding when using an inert placebo, and the possibility that expectancy partly contributed to outcomes despite efforts to minimise it (recruitment of largely psychedelic-naïve volunteers, structured silent retreat, emphasis on individual practice). The sample was composed of experienced meditators and healthy volunteers, which limits generalisability. The authors also acknowledge that challenging psychological experiences can occur with both meditation and psychedelics and that careful screening, supportive setting, and supervision are important to reduce adverse events. They conclude that the findings support interactions between non-pharmacological variables (set and setting, mindfulness capacities) and psilocybin effects, and suggest potential for combining mindfulness training with psychedelic-assisted interventions to promote psychological well-being, while calling for further research to refine predictors and therapeutic applications.