Effects of Psilocybin on Religious and Spiritual Attitudes and Behaviors in Clergy from Various Major World Religions

Psychedelic compounds such as psilocybin can occasion subjective states often described with religious or spiritual language, including experiences of unity, a felt sense of revelation (noetic quality), transcendence of time and space, intense positive mood, and ineffability. Previous prospective studies and survey research have linked psilocybin-occasioned mystical experiences with sustained improvements in wellbeing, meaning, and spiritual significance, and historical and anthropological records document sacramental uses of psychedelics in some Indigenous and religious traditions. Despite this background, little experimental work has examined how professionally trained clergy—individuals formally educated in theology and engaged in religious leadership within major world religions—experience and interpret psilocybin sessions. Griffiths and colleagues designed an exploratory, randomised, parallel-group waitlist study to evaluate the acute safety and both short- and long-term effects of two supported psilocybin sessions in psychedelic-naïve clergy from several major world religions. The study aimed to characterise persisting changes in psychological functioning, spiritual attitudes and practices, well-being, and vocational effects attributed to psilocybin, with a pre-registered Interim Questionnaire administered 6 months after enrolment to compare those who received psilocybin immediately with a delayed (waitlist) control group. The investigators hypothesised that, following the intervention, clergy would report increases in wellbeing, life satisfaction, spiritual practices, and positive changes in attitudes and behaviours relevant to their religious vocation.

Participants were required to hold recognised leadership positions with formal training and ordination (or equivalent) and to be regarded as unambiguous representatives of their religion. Recruitment used internet and print notices; approximately 100 people were telephone-screened, 37 provided informed consent for in-person screening, 33 met inclusion criteria and were randomised. The trial was conducted at two US sites (Johns Hopkins University and New York University) with institutional review board oversight. An urn randomisation procedure balanced groups on gender (female/male) and age (<55/≥55 years). The CONSORT flow information in the extract indicates several post-randomisation discontinuations for medical or protocol reasons; the interim analysis included 29 participants and 24 participants completed both psilocybin sessions and the longer follow-up schedule. A randomised parallel-group waitlist design was used: the Immediate Group received two psilocybin sessions soon after screening, while the Delayed Group served as a control through the 6-month interim assessment and then received the same intervention. The psilocybin intervention followed a standard supportive protocol with four preparatory meetings (about 8 hours total) conducted by two staff facilitators to build rapport and review safety, two dosing sessions about one month apart administered in a living-room‑like setting with two facilitators present, and three integration meetings (about 3 hours total) after each dosing session. All participants received 20 mg/70 kg in session 1; session 2 was 20 or 30 mg/70 kg depending on response and discussion with staff. Psilocybin was given orally in opaque capsules, sessions lasted about 8 hours, participants were encouraged to use eyeshades and headphones, and a preselected music programme was played. Primary and secondary outcomes were largely self-report. The pre-registered primary outcome for between-group comparison at 6 months was the Interim Questionnaire, an exploratory measure developed for the study asking about spiritual experiences and changes in spiritual practices, attitudes, mood, social interactions and vocational behaviours over the prior 5 months. Acute-session instruments included the MEQ30 (Mystical Experience Questionnaire), a modified Mysticism Scale (adapted to reference the session), an End-of-Session retrospective questionnaire, and the Challenging Experience Questionnaire. Persisting effects were assessed with a Retrospective Psilocybin Session and Persisting Effects Questionnaire at 4 and 16 months after the second session, including items tailored to religious vocation (e.g., enrichment of prayer/meditation, effectiveness as a religious leader). Cardiovascular measures and facilitator ratings were recorded during sessions, and adverse events were monitored. The extracted text notes additional secondary exploratory measures in supplementary material. Statistical analyses were conducted in R. Between-group categorical comparisons used Pearson's chi-square; within-person categorical changes used McNemar's test. Welch's t-test was used for unpaired continuous comparisons and paired t-tests for within-person comparisons. Effect sizes were reported as Cohen's d and correlations as Pearson's r. The significance threshold was p < 0.05. Because the study was exploratory, the authors did not correct for multiple comparisons and cautioned that this increases the risk of type I error.

Sample composition and follow-up: Of 33 randomised participants, the interim analysis included 29 participants (mean age 49.8 years, 31% female, 97% White, 93% with postgraduate degrees) and 24 participants completed both psilocybin sessions and the 4- and 16-month follow-ups. The sample represented four major world religions, predominantly Christianity (76%), with smaller representation of Judaism (17%), Islam (3%), and Buddhism (3%). Several participants discontinued for medical or protocol reasons (e.g., elevated blood pressure, undisclosed aortic aneurysm, incorrect dosing), but no serious adverse events were reported. Between-group (primary) outcomes at 6 months: On the Interim Questionnaire completed 6 months after screening, the Immediate Group (n = 13) who had received psilocybin differed significantly from the Delayed Group (n = 16) across a range of measures assessing experiences, attitudes, behaviour and wellbeing over the prior 5 months. Notably, 62% of the Immediate Group versus 0% of the Delayed Group reported having had a spiritual experience they rated among the five most spiritually significant of their lifetime. The Immediate Group scored significantly higher on five of seven items assessing positive changes in religious attitudes and behaviour and on seven of nine positive religious-attitude items (for example, feeling more effective as a religious leader). The Immediate Group also reported greater positive changes in mood, altruism, spirituality, life satisfaction and personal wellbeing; on several negative-change items the Delayed Group scored higher but with smaller effect sizes. Acute session effects (N = 24 completers): Among those who completed both sessions, 75% received an increased second dose of 30 mg/70 kg and 25% remained at 20 mg/70 kg. Physiological and facilitator-rated time courses were typical for psilocybin with onset by 30 minutes and peak effects between about 113 and 159 minutes. Mean MEQ30 Total scores were 82 and 80 for the 20 mg and 30 mg sessions, respectively, with 75% and 71% meeting a priori criteria for a "complete" mystical experience on sessions 1 and 2; 88% met criteria on one or both sessions. Participant retrospective ratings about 7 hours post-dose indicated high spiritual, meaningful and insightful qualities; peak joy, sense of peace and overall liking were described as intermediate between "Strong" and "Extreme." Persisting effects at 4 and 16 months (N = 24): Across 40 assessed items or scales, only four differed significantly between 4 and 16 months (all higher at 16 months), so the authors focused on 16-month outcomes. At 16 months, 96% of participants rated the psilocybin session experience among the top five most spiritually significant experiences of their life; 92% rated it among the top five most profound sacred experiences, and 42% rated it the single most profound sacred experience. Regarding noetic attributions, 54% rated the sacred experience as showing something "absolutely true" and 38% rated its truth as "strong." Most participants (79%) reported increases in contemplative/prayer/meditation practices, increased effectiveness in their vocation, and an increased daily sense of the sacred. When participants attributed changes to their psilocybin sessions, the mean endorsement of moderately or strongly positive changes across seven religious-attitude and behaviour domains was 65% (range 54–71%); mean endorsement of moderately or strongly negative changes was 2% (range 0–4%). Non-religious persisting effects: At 16 months, 88% endorsed moderately or strongly positive changes in personal wellbeing or life satisfaction, 83% endorsed positive changes in attitudes about self and life unrelated to vocation, and 54% endorsed positive changes in non-vocational behaviour; 0–4% endorsed negative changes in these domains. The lifetime Mysticism Scale total increased from a screening mean of 211.88 to 252.38 at 4 months (p < 0.001) and to 265.83 at 16 months (p < 0.001 vs screening; p = 0.005 for 16 months vs 4 months). Vocational outcomes and burnout: At screening, 71% reported having at some point seriously considered leaving their vocation; current consideration at screening was 8%. At 4 and 16 months after the second session, 25% and 17%, respectively, reported currently considering leaving their vocation; these rates were not statistically different from screening. Burnout ratings were low at screening (mean ≈1.00 on a 0–3 scale) and did not change significantly at interim, 4- or 16-month assessments. Adverse events: No serious adverse events occurred. The extract refers to supplementary tables listing adverse effects during and after 20 mg and 30 mg doses; a few participants were discontinued for medical concerns or reported transient physically challenging symptoms during sessions that resolved without sequelae.

Griffiths and colleagues interpret the results as indicating that psychedelic-naïve, professionally trained clergy from four major world religions reported substantial religious and non-religious benefits following supported psilocybin sessions. In the primary between-group comparison at 6 months, clergy who received psilocybin reported significantly greater positive changes in religious practices, attitudes about their vocation, appreciation of other traditions, spiritual awareness in daily life, and perceived effectiveness as spiritual leaders, along with improvements in mood and life satisfaction, compared with delayed controls. Follow-up data in those who completed both sessions showed that these attributions and increases in lifetime mystical experience scores were largely sustained through 16 months. The study team positions this trial as an advance on the historical Good Friday Experiment by enrolling professionally engaged clergy from multiple religions, using individual rather than group dosing, adopting a dyad facilitator model with screening, preparation and integration, administering two sessions, and adding measures tailored to vocational outcomes. They suggest potential future directions such as larger, more rigorous trials in clergy samples; investigations of psychedelic-facilitated experiences in religious education and interfaith tolerance; and the role chaplains might play as facilitators in palliative care contexts. At the same time, the authors caution against overgeneralisation and inflated expectations. They emphasise the need to study short- and long-term risks more thoroughly, including the possibility of epistemic harm—development of false or maladaptive beliefs—and social consequences that could arise if psychedelic experiences reinforce unfounded supernatural explanations. Methodological limitations are acknowledged: small and demographically skewed sample (primarily White, male, married, highly educated), self-selection and expectancy bias, limited religious representation (no Indigenous traditions, Hinduism, Taoism, Confucianism), reliance on self-report and some unvalidated measures, and the use of a waitlist rather than an active pharmacological control. The authors note that study advertising and the phrasing of questions referencing "sacred experience" may have biased responses. They also acknowledge that the operationalisation of "mystical experience" follows a particular scholarly tradition and that the study did not assess a broader range of adjacent conscious states.

The authors conclude that, in this small exploratory sample, two supported psilocybin sessions in psychedelic-naïve clergy were experienced as religiously significant, meaningful, and generally beneficial, with a pattern of adverse effects similar to prior psilocybin studies and no serious adverse events reported. They infer that further research involving religious leaders can proceed with reasonable safety when rigorous screening, informed consent, preparation, monitoring and integration are provided. Finally, the authors recommend larger, well-controlled trials including diverse religious and non-religious populations to better understand how worldview and cultural expectancies shape psychedelic experiences and their consequences.