Mystical experiences occasioned by the hallucinogen psilocybin lead to increases in the personality domain of openness

Maclean and colleagues situate their study within evidence that classic hallucinogens such as psilocybin, acting primarily at 5-HT2A receptors, can produce profound subjective changes and, in uncontrolled reports, lasting alterations in attitudes, values and behaviour. The paper highlights mystical-type experiences—characterised by unity, sacredness, ineffability, noetic quality and transcendence of time and space—as candidate mechanisms for enduring change. At the same time, the authors note that core personality traits, as described by the five-factor model (Neuroticism, Extroversion, Openness, Agreeableness, Conscientiousness), are typically stable in adulthood and that prospective, experimentally controlled demonstrations of personality change in healthy adults are lacking. This study combines data from two double-blind controlled investigations to test whether a single high dose of psilocybin (30 mg/70 kg) administered under supportive conditions produces changes in the five broad personality domains measured by the NEO Personality Inventory. Consistent with prior observations linking hallucinogen-occasioned mystical experiences to enduring personal change, the investigators hypothesised that individuals who experienced mystical-type effects during the high-dose session would show enduring increases in Openness assessed 1–2 months after the session and again more than 1 year later.

Participants were community volunteers recruited for laboratory studies of psilocybin. After telephone pre-screening and in-person medical and psychiatric evaluation, the analyses included 52 hallucinogen-naïve participants (one participant was excluded for incomplete personality data and one for prior psilocybin experience). The sample was generally highly educated and reported regular spiritual activity; participants were not paid and provided informed consent under institutional review board approval. Maclean and colleagues combined two double-blind designs. In Study 1 each participant completed 2–3 eight-hour sessions and received one high psilocybin dose (30 mg/70 kg) and an active control (methylphenidate 40 mg/70 kg) on other sessions. In Study 2 participants completed five sessions with ascending or descending psilocybin doses (5, 10, 20 and 30 mg/70 kg) and a placebo session; the present analyses focus on effects associated with the 30 mg/70 kg session. Sessions were separated by at least 3 weeks. Preparation and support were extensive, and during sessions participants were encouraged to lie down, wear an eye mask, listen to a standard music programme, and focus inward. Primary outcome measurement was the revised NEO Personality Inventory (NEO‑PI‑R), administered at screening, 1–2 months after the high-dose session (post-test), and at approximately 14 months follow-up. Mystical-type experiences during sessions were assessed about 7 hours after drug administration with the States of Consciousness Questionnaire (SOCQ), which yields six subscales; a 'complete mystical experience' was predefined as scoring 60% or higher on each subscale. Additional session measures included a modified Mysticism Scale (lifetime and experience-specific), and the APZ instrument with scales for oceanic boundlessness (OSE), visionary restructuralization (VUS), and dread of ego dissolution (AIA). Scores were standardised where appropriate (NEO T scores: M = 50, SD = 10). Statistical analyses were performed in SPSS v18.0. The core approach used multivariate repeated measures ANOVA to test change from screening to post-test across the five NEO factors, followed by Pearson and Spearman correlations between Openness change and session measures. Stepwise linear regressions tested whether SOCQ mystical scores explained additional variance in Openness change beyond other correlated questionnaires (Mysticism Scale, OSE, VUS, AIA). Finally, the investigators compared participants who met the pre-specified criteria for a complete mystical experience (n = 30) with those who did not (n = 22) to examine group-by-time interactions in Openness and its six facets.

Across the combined sample, Openness increased significantly from screening to the 1–2 month post-test (mean change +2.8 T points; F(1,51) = 5.47, p = 0.023, partial eta squared = 0.10). A subgroup analysis of participants who did not receive a high dose on their first session (n = 30) showed no significant Openness change after that first session (F(1,29) = 0.52, p = 0.48). The other four NEO factors showed no significant mean changes from screening to post-test: Neuroticism (mean −0.5; F(1,51) = 0.24, p = 0.62), Extroversion (mean +0.8; F(1,51) = 0.79, p = 0.38), Agreeableness (mean +1.7; F(1,51) = 2.31, p = 0.16), and Conscientiousness (mean −0.9; F(1,51) = 1.22, p = 0.28). Test–retest correlations across assessments ranged from r = 0.61 to 0.84, indicating overall trait stability. Individual differences in mystical-type experience correlated with Openness change. SOCQ mystical scores (mean across six subscales) correlated with increases in Openness (r = 0.42, p = 0.002), and this relationship held with Spearman rank correlations (r_s = 0.47, p < 0.001). Other session measures also correlated with Openness change: Mysticism Scale (r = 0.33, p = 0.017), OSE (r = 0.44, p = 0.001), VUS (r = 0.41, p = 0.003), and AIA (r = 0.31, p = 0.024). Stepwise regression analyses indicated that SOCQ mystical score accounted for significant additional variance in Openness change beyond each of these alternate measures. Reported R-squared change values for adding SOCQ to models already including another questionnaire were: Mysticism Scale ΔR2 = 0.046 (p = 0.033), OSE ΔR2 = 0.047 (p = 0.031), VUS ΔR2 = 0.042 (p = 0.036), and AIA ΔR2 = 0.12 (p = 0.001). Comparing groups defined by the a priori 'complete mystical experience' criterion revealed a significant time × group interaction on Openness (F(1,50) = 9.32, p = 0.004, partial eta squared = 0.16). Participants who met the complete mystical experience criteria (n = 30) showed a robust increase in Openness from screening to post-test (mean +5.7; t(29) = 3.44, p = 0.002), whereas those who did not meet the criteria (n = 22) did not (mean −1.2; t(21) = 0.87, p = 0.39). Five of the six Openness facets—Fantasy, Aesthetics, Feelings, Ideas and Values—showed the same interaction pattern; the Actions facet did not reach significance. At long-term follow-up (mean 16 months), participants who had a complete mystical experience maintained higher Openness relative to screening (mean +4.2; F(1,29) = 4.17, p = 0.050, partial eta squared = 0.13), with no significant decline from the post-test level. Participants without a complete mystical experience had virtually unchanged Openness at follow-up compared with screening (mean −0.3; p = 0.86). The investigators note that results were similar across the two component studies, and including three participants who had a complete mystical experience at a 20 mg session (but not at 30 mg) did not alter findings.

Maclean and colleagues interpret their findings as evidence that a single high-dose psilocybin session, administered under supportive conditions, produced statistically and clinically meaningful increases in the personality domain of Openness in healthy adults. They emphasise that the magnitude of change for participants who had a complete mystical experience (more than 4 T-score points from screening to follow-up) exceeds typical age-related shifts in Openness (about 1 T-score point per decade) and is larger than some changes reported following other interventions such as antidepressant treatment or intensive counselling. The authors link increases in Openness to the content of mystical-type experiences: Openness encompasses aesthetic appreciation, imagination, emotional awareness and intellectual engagement, and significant increases across nearly all Openness facets suggest potential gains in aesthetic and cognitive domains. They contrast their positive long-term findings with a prior controlled LSD study that failed to demonstrate personality change at 6 months, and suggest that differences in participant motivation, preparatory support and spiritual orientation may account for divergent outcomes. The SOCQ emerged as a stronger predictor of Openness change than other session measures; however, the investigators acknowledge that the SOCQ has limited published psychometric validation and that continued evaluation of its sensitivity and validity is needed. They also discuss alternative personality inventories such as the Temperament and Character Inventory and suggest that related constructs (for example, Self-Transcendence) might also change following mystical-type experiences. Key limitations noted by the authors include the need for replication in larger and more diverse samples, the self-selected nature of the sample (many participants were spiritually active and highly motivated), and the fact that the study examined change after a single high-dose session. They acknowledge that multiple sessions might affect additional personality domains and that clinical populations might show different patterns (for example, decreases in Neuroticism have been observed in other treatment contexts). Finally, the investigators outline implications for clinical psychiatry and future research: the findings motivate further investigation of biological and psychological mechanisms linking psilocybin and mystical experience to personality and suggest examining how pharmacological and non-pharmacological conditions might occasion mystical experiences and their long-term consequences.