Decreases in State and Trait Anxiety Post-psilocybin: A Naturalistic, Observational Study Among Retreat Attendees

Anxiety disorders are highly prevalent and burdensome worldwide, yet existing treatments yield only partial response rates (typically around 50–58% for pharmacological or cognitive-behavioural approaches). Historical and contemporary research has suggested that psychedelic substances—including psilocybin—can reduce anxiety symptoms in clinical and naturalistic samples, sometimes producing durable effects after a single administration. Two psychological candidates for mediating such effects are reductions in the personality trait neuroticism and enhancements in mindfulness capacities; additionally, the intensity or quality of the acute psychedelic experience (for example, ego dissolution) has been linked to longer‑term outcomes in prior work. Kiraga and colleagues designed a naturalistic observational study to examine whether ingestion of psilocybin-containing truffles in a supportive retreat context produces sub-acute and one‑week reductions in state and trait anxiety among volunteer attendees. The investigators also set out to test whether post‑retreat changes in mindfulness and neuroticism occur, and whether these psychological changes—or acute ratings of ego dissolution—predict reductions in state and trait anxiety. The study therefore aimed to characterise short-term anxiolytic effects and potential psychological mechanisms in a real‑world group setting.

Participants were adult volunteers attending legal psilocybin retreats in the Netherlands organised by the Psychedelic Society UK. Inclusion required being at least 18 years old and proficient in English; facilitators conducted pre-retreat intakes that screened out individuals with psychiatric disorders or on psychiatric medications and other medical risk factors. Ethics approval was obtained from Maastricht University's Ethics Review Committee (ERCPN-175_03_2017_A5), participation was voluntary, and the research team did not take part in retreat organisation or facilitation. Assessments occurred at three time points: baseline (the evening before ingestion), sub-acute (within 24 hours after ingestion; the morning after), and follow-up (7 days post-ingestion, completed online). Retreat participants consumed psilocybin‑containing truffles prepared as tea in a consistent retreat setting with facilitators, music and group support. The total truffle mass consumed per participant was recorded and a truffle sample was analysed by HPLC to determine psilocybin and psilocin content; the authors report an average psilocin consumption of 27.1 mg per participant after accounting for metabolic conversion. Measures included the State‑Trait Anxiety Inventory (STAI; state and trait scales), the Five Facet Mindfulness Questionnaire (FFMQ; five facets), and the Big Five Inventory (BFI; administered at baseline and follow-up). The Ego Dissolution Inventory (EDI) was completed at the sub‑acute session to quantify the acute experience, and a shortened Persisting Effects Questionnaire (PEQ) was administered at day 7 to assess lasting subjective effects. All instruments were in English. For statistical analysis the investigators fitted separate ordinary least squares multi‑linear regression models for each outcome with Session (baseline, sub‑acute, follow-up) as a categorical predictor and performed contrasts comparing baseline to sub‑acute and baseline to follow‑up. Descriptive statistics were computed for EDI and PEQ items. To examine multivariate associations among psychological predictors and anxiety outcomes, canonical correlation analyses were conducted using follow‑up non‑judge FFMQ scores, follow‑up neuroticism scores, and EDI scores as predictors and sub‑acute and follow‑up state and trait anxiety as criterion variables. The alpha significance threshold was p ≤ 0.05 and reported Cohen's d effect sizes for significant effects.

Sample and dose: Fifty‑five volunteers provided informed consent (mean age 34.8, SD 8.9; 47% male, 47% female, 5% other). Most were European (80%) and many had prior psychedelic experience. Participants ingested a mean 34.2 g (SD 8.9) of truffles, and analysis of a 15 g sample (Psilocybe Hollandia) detected 1.9 mg psilocybin and 10.5 mg psilocin; using a conversion factor the authors report an average psilocin consumption of 27.1 mg. Attrition across assessments was notable: depending on the measure, completion counts were lower at the sub‑acute and follow‑up time points (for example, STAI completed by 46 at baseline, 42 at sub‑acute, and 22 at one week). Primary anxiety outcomes (STAI): Ordinary least squares regression revealed a significant main effect of Session on state anxiety (F2,107 = 14.10; p < 0.001). Compared with baseline, state anxiety was reduced by 6.4 points the morning after ingestion (p < 0.001; d = 0.77) and by 6.7 points at one week (p = 0.001; d = 0.87). Trait anxiety also showed a significant Session effect (F2,107 = 10.13; p = 0.002): trait anxiety was about 6.0 points lower the morning after (p = 0.014; d = 0.52) and 8.6 points lower at one week (p = 0.004; d = 0.77) on the 20–80 STAI scale. Mindfulness (FFMQ) and personality (BFI): FFMQ completion counts were 52 at baseline, 46 at sub‑acute and 23 at follow‑up. A significant Session effect emerged for the Non‑judge facet (F2,118 = 4.37; p = 0.04). The contrast versus baseline showed a non‑significant 0.5 increase the morning after (p = 0.39; d = 0.17) and a significant 1.5 point increase at one week (p = 0.03; d = 0.51). No significant Session effects were detected for the other FFMQ facets. BFI data (48 at baseline, 23 at follow‑up) showed significant Session effects for Neuroticism (F1,69 = 8.46; p = 0.005) and Agreeableness (F1,69 = 8.87; p = 0.004). At one week participants scored 5.2 points lower on neuroticism compared with baseline (d = 0.76) and 3.8 points higher on agreeableness (d = 0.78). No significant changes were reported for the remaining three traits. Acute and persisting subjective effects: The EDI was completed by 47 participants at sub‑acute; mean EDI = 59.7 (SD 28.3), range 3–100. The PEQ was completed by 20 participants at day 7. On the PEQ items assessing personal meaningfulness and spiritual significance, a substantial proportion rated the experience among the most meaningful or spiritually significant of their lives (for example, 10% rated it the single most meaningful experience, 50% among the 5 most meaningful). Psychological challenge and insight were also variably reported: 35% rated the experience as the single most psychologically insightful experience of their life. Hypothesis‑driven multivariate associations: Canonical correlation analysis used three predictor variables (follow‑up Non‑judge FFMQ, follow‑up neuroticism, and EDI) and four anxiety outcome variables (sub‑acute and follow‑up state and trait anxiety). Three canonical functions had squared canonical correlations (Rc2) of 0.891, 0.324 and 0.096. The full model was significant (F[12,18.81] = 2.81; p = 0.022), and the authors treated the first two functions as noteworthy. Function 1 suggested that reductions in neuroticism were the dominant predictor of changes in trait anxiety, explaining the largest share of covariance. Function 2 implicated higher EDI scores (stronger ego dissolution) as the dominant predictor of reductions in state anxiety.

Kiraga and colleagues interpret the findings as evidence that a single administration of psilocybin in a supportive retreat context was associated with medium to large reductions in both state and trait anxiety that persisted for at least one week. The investigators also observed increases in the Non‑judge facet of mindfulness and decreases in trait neuroticism, and consider reductions in neuroticism and the intensity of ego dissolution to be the strongest correlates of reduced trait and state anxiety, respectively. The authors situate these results alongside historical and modern studies showing anxiolytic effects of psychedelics in clinical populations (including patients with life‑threatening illness and treatment‑resistant depression) while noting mixed outcomes in laboratory studies of healthy volunteers. They highlight that the present naturalistic findings are consistent with reports that psychedelic experiences can induce relatively rapid and durable changes in personality (notably neuroticism) and that ego dissolution or other intense acute experiences often correlate with longer‑term positive outcomes. Several limitations and uncertainties are acknowledged. Most importantly, the naturalistic observational design lacks experimental control—there was no placebo or comparator condition and retreat variables (setting, facilitator support, exact dosing and timing) were not controlled. Attrition reduced sample sizes at later time points and could introduce bias; the authors note that attrition predictors in web‑based psychedelic studies have paralleled those in other fields and that prior work did not find attrition to be driven by advocacy or negative experiences. The investigators also caution that it remains unclear whether intense subjective experiences such as ego dissolution are necessary causal mechanisms for longer‑term benefits or whether they are epiphenomena of underlying neurobiological actions, and that other psychological processes (for example, insight, catharsis or suggestibility) may be relevant. In terms of implications, the authors call for controlled experimental studies to disentangle pharmacological and extra‑pharmacological contributors (set and setting) to treatment outcomes, and propose that group‑based psychedelic interventions merit further study as a potentially more scalable and cost‑effective modality, subject to rigorous evaluation of feasibility, safety and efficacy.

The study concludes that ingestion of psilocybin in a supportive group retreat was associated with persisting reductions in state and trait anxiety and in trait neuroticism, together with increases in a mindfulness facet (non‑judgement) up to one week after the experience. The authors recommend systematic investigation of the role of set and setting and further research into group formats for psychedelic‑assisted interventions to inform optimisation and potential cost‑effectiveness of therapeutic programmes.