Modulatory effects of ayahuasca on personality structure in a traditional framework

Netzband and colleagues frame ayahuasca as an Amazonian plant brew containing DMT plus MAO inhibitors, used traditionally in ceremonial contexts and increasingly by international ‘ayahuasca tourists’. The introduction notes mechanistic links between serotonergic 5-HT2A receptor agonism and alterations in brain networks such as the default mode network, and it summarises prior human and animal evidence that single or occasional administrations of serotonergic psychedelics (including psilocybin and ayahuasca) can produce rapid antidepressant effects and longer-term changes in mood, cognition and some personality domains. Building on earlier studies that reported increases in openness and other trait-level changes after psychedelics, the study aimed to evaluate whether participation in a 12-day, Shipibo-style ayahuasca retreat adapted for tourists would modulate personality structure. The investigators set out to measure short-term (post-retreat) and six-month follow-up changes in Big Five personality domains (using the NEO-PI3), and to test whether the intensity of perceived mystical experience (MEQ30) related to any personality changes. The setting was an indigenous Shipibo community–based retreat in the Peruvian Amazon that caters to international participants.

This was an observational repeated-measures field study conducted at the Ayahuasca Foundation, a retreat centre in the Allpahuayo-Mishana Reserve near Iquitos. Each 12-day retreat included six ayahuasca ceremonies held every other evening in a traditional circular building (‘maloka’). Ceremonies were led by a local curandero and facilitators, ran about 6 hours, and involved silent individual reclining in darkness with traditional songs ('icaros'). Dosing was determined by the curandero and the individual's will on the day; no fixed doses or chemical constituent analyses were performed. Medical support and optional remote aftercare counselling were provided, and participants were encouraged to abstain from other substances for 2 weeks prior to the retreat, though medical records were not independently checked. Twenty-four English-speaking retreat participants (15 males, 9 females; mean age 37.6) comprised the active group. About half reported a current or historical psychiatric diagnosis (depression, anxiety, PTSD); some reported chronic or resolved physical ailments. A matched comparison group of 24 English-speaking tourists (11 males, 13 females; mean age 32.6) was selected from an initial pool of 65 holidaying individuals who reported no prior ayahuasca experience. Groups did not differ significantly on age, gender, education level, or reported psychiatric/physical health history by the tests reported. Primary outcome measures were personality domains assessed with the NEO-PI3 (five domains, each with six subfacets) at baseline (day before first ceremony), immediately post-retreat (after six ceremonies), and at 6-month follow-up (electronic). The Mystical Experience Questionnaire (MEQ30) was administered post-retreat to quantify subjective mystical-type experiences. Statistical analysis used a mixed ANOVA with time and personality domain as within-subject variables and group (active vs comparison) as a between-subject variable; Benjamini-Hochberg correction with an FDR of 0.1 was applied for multiple comparisons and Greenhouse-Geisser corrections used where sphericity was violated. Spearman rank correlations examined associations between personality change scores and MEQ30.

The active group comprised 24 retreat participants; three did not provide 6-month NEO data, leaving 21 active subjects for long-term analyses. Baseline comparisons indicated no significant difference in neuroticism between groups (Mdiff = 6.71, 95% CI -8.49 to 21.91, p = .379, d = 0.26). Mixed ANOVA results indicated a significant interaction of time, personality, and group (Pillai's trace = 0.22, F(3.17, 136.24) = 4.32, p = .005, partial η2 = .09), driven principally by reductions in neuroticism and increases in agreeableness in the active group. Pairwise comparisons showed a significant short-term increase in agreeableness in the active group from baseline to post-test (Mdiff = 10.13, 95% CI 2.34 to 17.91, p = .012, d = 0.45) but not in the comparison group. There was a trend toward increased openness from baseline to post-test in the active group (Mdiff = 6.92, 95% CI 0.32 to 13.51, p = .040), though this did not survive correction for multiple comparisons. Neuroticism reduction in the active group correlated with intensity of reported mystical experience: a medium, significant negative Spearman correlation between neuroticism change and MEQ30 scores was observed, r_s(48) = -0.56, p < .001. Baseline neuroticism did not correlate with MEQ30 (r_s = .02, p = .883), implying the association related to change rather than starting level. Change in agreeableness did not correlate significantly with MEQ30 (r = 0.18, p = .211). At 6-month follow-up (n = 21 active; n = 24 comparison), reductions in neuroticism observed post-retreat remained stable in the active group and were significantly lower than in the comparison group. Reported means at follow-up were: active neuroticism M = 75.91 (SEM = 4.26) versus comparison M = 109.83 (SEM = 3.99), with the group difference p < .001, d = 1.71. The short-term increase in agreeableness persisted at 6 months (active M = 119.33, SEM = 3.12). Additionally, openness to experience was significantly greater in the active group at 6 months (active M = 135.48, SEM = 2.98; comparison M = 117.08, SEM = 2.79; Mdiff = 18.39, 95% CI 10.15 to 26.63, p < .001, d = 2.20).

Netzband and colleagues interpret their findings as evidence that participation in a 12-day Shipibo-style ayahuasca retreat adapted for tourists produced significant reductions in neuroticism that persisted at 6 months, alongside sustained increases in agreeableness and later-emerging increases in openness. The observed association between greater mystical-type experience (MEQ30) and larger reductions in neuroticism is highlighted as consistent with prior psilocybin and ayahuasca studies that linked the subjective intensity of the acute experience to longer-term personality and clinical outcomes. The authors situate their results within existing literature showing personality change after serotonergic psychedelics, noting partial concordance with earlier reports of increased openness and reduced neuroticism. They caution that their sample already reported relatively high openness at baseline, which may have limited detectable short-term increases. Neurobiological mechanisms are discussed speculatively, with reference to animal data suggesting serotonergic psychedelics may enhance neuroplasticity; the authors note those preclinical findings have not been replicated in vivo in humans and thus transferability remains speculative. Several limitations are emphasised. The field, observational design exposed the study to uncontrolled confounders and limited capacity for biological or pharmacokinetic measurement. No standardised dosing or chemical analysis of ayahuasca batches was performed, and non-psychoactive plants and other retreat practices could have influenced outcomes. Participant selection relied on self-report for medical history and abstinence from other substances, with no verification of medical records or drug testing. Self-selection bias, a modest sample size, and the absence of randomisation or blinding restrict causal inferences and generalisability. The authors discuss therapeutic implications cautiously, suggesting reductions in neuroticism and increases in agreeableness may have relevance for affective disorders and some personality pathology, while acknowledging that the clinical meaning of increased agreeableness is less clear. They advocate for further research comparing outcomes between clinical and non-clinical populations and for trials in varied settings (neo‑shamanic, clinical) to clarify the roles of pharmacology, the subjective experience, and set and setting in mediating change. Ethical concerns about the growth of ayahuasca tourism are also outlined, including risks from untrained ‘neoshamans’, lack of regulation, possible exploitation, and cultural appropriation. The authors recommend more rigorous, regulated research to evaluate efficacy and safety across different frameworks.