The revival of interest in psychedelic medicines has two primary strands. First, laboratory-based clinical research focusing on therapeutic applications of serotonergic psychedelic compounds (i.e., 5-HT2A receptor agonists, e.g., psilocybin, LSD) has yielded some evidence of long-term changes in personality1,2 and positive mental health outcomes3,1. Second, a parallel interest in shamanic medicine using psychedelic compounds (e.g., huachuma, ayahuasca) has also emerged but has received considerably less research attention. The ceremonial use of plants containing 5-HT2A receptor agonists dates back at least three thousand years, involving numerous early cultures including the Vedic culture of northern India5, and Aztec6,7, Native American8, and Grecian9 cultures.
The purpose of this study is to examine personality change following the ceremonial use of ayahuasca, a decoction combining the woody vine Banistereopsis caapi10,11 (containing β-carboline monoamine oxidase inhibitors) and plants containing the 5-HT2A receptor agonist N,N Dimethyltryptamine (DMT; e.g., the shrub Psychotria viridis12). Personality change is important to understand because personality is related to a wide array of important outcomes (e.g., occupational success13; physical health and mortality14), and serves as the foundation for many models of psychopathology (e.g., HiTOP15). Because personality change effects may depend on other measurable factors, we also examined the degree to which predisposing factors, such as demographic characteristics and baseline personality, and experiential factors, such as non-ordinary states of affect and consciousness during ceremony, moderate personality changes.
The Importance of Studying Ayahuasca in the Ceremonial vs. Laboratory Setting
Ayahuasca was prepared as early as one thousand years ago16 and is thought to have a long history of ceremonial use among indigenous peoples of Brazil and the Amazonian basin of South America17,7. Within the last twenty-five years, ayahuasca healing centers have become sources of alternative mental health treatment among Westerners, particularly those whose symptoms have shown recalcitrance to change using Western approaches. In view of a long period of development, ceremonial practices may be informative about key elements of psychedelic-assisted experience that potentiate positive psychological changes. Furthermore, exploring approaches to healing that lie outside the Western scientific tradition is congruent with recent calls to revise Western epistemological biases that circumscribe scientific understanding18,19. Ayahuasca ceremonies combine numerous elements which may play a role in whatever personality change is found, including communal/group formats, guiding elements (e.g., chanting of prayer during ceremony, use of adjunct plants such as tobacco, perfumated water), engagement with a shaman (e.g., icaro [medicine prayer] delivered by the shaman), and engagement with personal challenges (e.g., purgative aspects, emotional intensity, traumatic reexperiencing). Purging, occurring generally within the first two hours of ceremony, is typically preceded by digestive discomfort, and accompanied by feelings of physical and emotional relief.
A further element that deserves consideration is the philosophical framework within which shamanic traditions understand the therapeutic process. For Shipibo shamans, the ayahuasca decoction is regarded as a pandora’s box (or amplifier) that facilitates attunement to spirits (those inclined toward revelations of unity between self and world [unitive consciousness] or perpetuation of separateness), and is thought to constitute a spirit itself aiding in the healing process. Furthermore, the shaman’s icaro – regarded as originating from previously “dieted” traditional plants/spirits – is thought to open up “portals” that guide positive spirits (operating as “muses” or “doctors”) to minister to “blockages of energy” within ceremony participants. These “blockages” are regarded as the sources of persisting separateness/ignorance obstructing unitive consciousness. The diet (“dieta”) process is worth highlighting because it is outside Western medical and scientific training. Dieta involves spending a period of time in isolation consuming a teacher plant (e.g., tobacco, coca) and focusing on its psychospiritual effects. Ideally, the spirit of the plant reveals itself and becomes an ally of the student (correspondence with anonymous Shipibo-trained shaman). Many of the Shipibo shamanic concepts presented here may be reduced in translation given their broad ontological context.
Psychedelic Research as a Window into Personality Change
To date, psychologists have observed a number of pathways by which personality changes, including normative development20, biological maturation21, genetic factors22, major life events23,24, new social and vocational roles25,26, commitment to new identities27,28, psychotherapy29,30, and self-motivation31,32. Although some evidence suggests that psychedelic compounds may offer an additional pathway, prospective studies in naturalistic and laboratory settings have yielded mixed evidence.
Prospective studies in controlled laboratory settings have shown heterogeneous effects that may depend in part on length of follow-up, sample size, conditions of administration, and experiences during the acute effects of the compounds. Changes in Five-Factor model (FFM33) Neuroticism (decreasing), Extraversion, Openness, Agreeableness, Conscientiousness (increasing), and Absorption34 have been reported across healthy35,36,2 and clinical1 samples. Furthermore, two naturalistic studies have observed adaptive personality changes - decreases in Harm Avoidance (i.e., characterized by worry37)38,39 and increases in Self-Directedness (i.e., adaptive capacity to achieve chosen goals)39, personality domains that largely map onto FFM domains of Neuroticism, Extraversion, and Conscientiousness. Nevertheless, meaningful changes in these domains have not always been observed40,41,42,43, and the emergence of stable changes may depend on inner experiences during the compound’s acute effects1,2,c.f.42,43.
Finally, five clinical studies, including two randomized placebo-controlled trials, have provided support for an antidepressant effect44,45,46,47. Given that many psychopathological symptoms are increasingly conceptualized as maladaptive variants of basic personality dimensions and share the same structure15,48, these results may be relevant to FFM Neuroticism and Extraversion.
In view of the empirical inconsistency in these findings and null results within placebo-controlled studies42, one must consider that observed changes in self-reported personality may be products of placebo, expectancy, and/or demand effects following particularly intense and compelling experiences49. Methodological limitations may also account for empirical inconsistency. First, existing studies tend to use small samples (mean N=19) and thus have lower statistical power, yield less precise estimates, and may be less generalizable. Second, even consistent findings have not been sufficiently replicated, with just two prospective examinations of ayahuasca-induced personality change having been published38,39. Third, few studies have corroborated self-reported change with observations of informant-reported change, which could reduce the influence of placebo, demand, and expectancy effects among target participants. Fourth, the majority of studies did not employ a control group, which can accompany validity threats including regression to the mean and the Hawthorne effect50. Notably, the single controlled laboratory study that included a control group did not show a statistically significant change in any personality domains42, though low sample size and statistical power would have limited its capacity to detect a smaller statistically significant effect. Finally, few studies have rigorously examined potential moderators (e.g., sample, design characteristics) which may provide the necessary conditions for change, or have been sufficiently well-powered to validly do so.
Ayahuasca Moderators: Set and Setting
Theoretical and empirical work have pointed to a number of predisposing and experiential factors as having potential to account for variability in the long-term effects of psychedelic compounds.
Predisposing factors. Predisposing factors roughly map onto popularly observed determinants of psychedelic experience, (mind)set and setting51, but also include individual differences such as baseline personality traits. Among previously examined predisposing factors, personality traits (e.g., Absorption, or one’s disposition toward total attentional engagement with one’s perceptual or ideational resources), affective states (e.g., emotional excitability), age, and experimental setting have shown associations with affective and mystical states during psychedelic experience1,52.
Experiential factors. A small literature has examined acute non-ordinary psychological states as potentiating factors in personality change1,2,4,40,42,43,52, 53,54. Among the most popular targets of inquiry are states of mystical-type and intense emotional experiences based on work indicating convergence between psychedelic, religious, psychodynamic (i.e., involving confrontation with self, emotion, and conflict), and transpersonal (i.e., involving continuity between mental, physical, and metaphysical life) phenomenology53,54,55,56. Previous findings have indicated that non-ordinary states of unitive consciousness (i.e., feeling of being one with a larger whole), insightfulness (i.e., perceptions of encounter with ultimate reality), awe, and transcendence from time and space (collectively referred to as mystical experience)57 may potentiate change in FFM Openness2,c.f.1,42,43, Neuroticism, and Extraversion1,58.
Present Study
The present study examined personality change in relation to the ceremonial use of ayahuasca in a sample of 256 participants using self- and informant-report measures of personality across three timepoints (i.e., Baseline, Post, 3-month Follow-up for self-report; Baseline, 3-month Follow-up for informant-report). Differences in self- and informant-report personality domain scores between timepoints were examined. In line with previous work1,2, self- and informant-report FFM Openness and Extraversion were hypothesized to increase, and FFM Neuroticism was hypothesized to decrease following initial measurement.
The second aim was to investigate factors that may affect the degree of personality change found in relation to psychedelic experience. Specifically, we examined the degree to which differences in FFM traits and facet scores between timepoints varied as a function of predisposing and experiential factors. In line with previous work2, mystical experience was hypothesized to contribute to a larger difference in FFM Openness between Baseline, on one hand, and Post and Follow-up, on the other. All hypotheses were preregistered using the Open Science Foundation web platform (https://osf.io/xk3ym).