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The International Journal for the Psychology of Religion
ISSN: (Print) (Online) Journal homepage: www.tandfonline.com/journals/hjpr20
Altered States of Consciousness During Ceremonial San
Pedro Use
Arne Bohn, Michiel H. H. Kiggen, Malin V. Uthaug, Kim I. M. van Oorsouw,
Johannes G. Ramaekers & Hein T. van Schie
To cite this article: Arne Bohn, Michiel H. H. Kiggen, Malin V. Uthaug, Kim I. M. van Oorsouw,
Johannes G. Ramaekers & Hein T. van Schie (2023) Altered States of Consciousness During
Ceremonial San Pedro Use, The International Journal for the Psychology of Religion, 33:4,
309-331, DOI: 10.1080/10508619.2022.2139502
To link to this article: https://doi.org/10.1080/10508619.2022.2139502
© 2022 The Author(s). Published with
license by Taylor & Francis Group, LLC. View supplementary material
Published online: 05 Dec 2022. Submit your article to this journal
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Altered States of Consciousness During Ceremonial San Pedro Use
Arne Bohn
a
*, Michiel H. H. Kiggen
a,b
*, Malin V. Uthaug
c,d
, Kim I. M. van Oorsouw
d
,
Johannes G. Ramaekers
e
, and Hein T. van Schie
a
a
Behavioural Science Institute, Radboud University, Nijmegen, The Netherlands;
b
Stevig Specialized and Forensic Care
for People with Intellectual Disabilities, Dichterbij, Oostrum, The Netherlands;
c
The Centre for Psychedelic Research,
Department of Brain Sciences, Faculty of Medicine, Imperial College, London, UK;
d
Department of Clinical
Psychological Science, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands;
e
Department of Neuropsychology and Psychopharmacology, Faculty of Psychology and Neuroscience, Maastricht
University, Maastricht, The Netherlands
ABSTRACT
San Pedro, a mescaline containing cactus, has been used for thousands of
years and is currently popular as a psychedelic substance in ceremonial
retreats in Europe. The current research investigates the consciousness alter-
ing eects of San Pedro. Forty-two participants who joined ceremonial
psychedelic retreats in the Netherlands were investigated with question-
naires probing 11 dimensions of altered states of consciousness (11D-ASC),
ego-dissolution, mystical experiences, and challenging experiences. Results
tentatively demonstrate the status of San Pedro as a psychedelic, revealing
deviations from normal waking consciousness on all 11 subscales of the 11D-
ASC, moderate scores of ego-dissolution, and a complete mystical experi-
ence in two thirds of the participants. Furthermore, a consciousness prole of
San Pedro was constructed, which revealed that spiritual experiences are
strongly expressed in ceremonial San Pedro use. Furthermore, the San Pedro
experience is characterized by low levels of disembodiment, anxiety,
impaired control and cognition, transcendence of space, and relatively
higher levels of physical distress and grief in case of (incidental) challenging
experiences. Finally, graph network analysis indicated two separate networks
of positive and negative altered states of consciousness. Possible interpreta-
tions of these ndings are discussed in relation to the ceremonial setting,
sympathomimetic eects of San Pedro’s alkaloids and variations in aective
valence.
San Pedro, Huachuma, or Echinopsis pachanoi is a psychoactive psychedelic plant from the family of
Cactaceae. Native to the South American Andes, San Pedro has a long history of being harvested by
indigenous societies, to be consumed as a medical plant sacrament during ceremonial rituals (Jay,
2019). Anno 2022, ceremonial San Pedro use has spread to western countries, where local ceremony
providers offer San Pedro to participants for its healing potential, among other reasons (Uthaug, Davis
et al., 2021). From research with other psychedelic drugs, we know that the altered states of
consciousness generated by psychedelics offer a growing range of therapeutic applications (Garcia-
Romeu et al., 2016), as well as psychological risks (Carbonaro et al., 2016). However, to this date, no
research has exclusively investigated the psychological effects of ceremonial San Pedro use. In order to
fill this hiatus in the literature and to aid the development of psychedelic assisted therapies, the current
CONTACT Michiel H. H. Kiggen michiel.kiggen@gmail.com Stevig Specialized and Forensic Care for People with Intellectual
Disabilities, Dichterbij, Wanssumseweg 14, 5807 EA, Oostrum, The Netherlands
*These authors contributed equally to this work.
Supplemental data for this article can be accessed online at https://doi.org/10.1080/10508619.2022.2139502
THE INTERNATIONAL JOURNAL FOR THE PSYCHOLOGY OF RELIGION
2023, VOL. 33, NO. 4, 309–331
https://doi.org/10.1080/10508619.2022.2139502
© 2022 The Author(s). Published with license by Taylor & Francis Group, LLC.
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://
creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the
original work is properly cited, and is not altered, transformed, or built upon in any way. The terms on which this article has been published allow the
posting of the Accepted Manuscript in a repository by the author(s) or with their consent.
study presents a first observational attempt to describe the effects of ceremonial San Pedro use on
human consciousness.
San Pedro, originally called Huachuma, originates in the highlands of the Andes and has been used
ceremonially for religious reasons as well as healing purposes. Archaeologists found evidence for
extensive ceremonial use as a holy plant, as well as stone carvings from around 1300 BCE in ruins of
the Peruvian Chavin culture, which depict humanoid figures holding a San Pedro Cactus (Jay, 2019).
In 1571, Spanish administrators noted the consumption of San Pedro by the natives under guidance of
a local shaman, and the accompanying Christian missionaries called Huachuma “the plant with which
the devil deceived the Indians of Peru in their paganism” (Jay, 2019, p. 25). Nonetheless, after
Christianization of South America, ritual consumption has been incorporated into the local
Christian belief systems and Huachuma was renamed after “Saint Peter, who holds the keys to heaven”
and is “suggestive of the plant’s power to open the gates between the visible and invisible worlds’’
(Heaven, 2010, p. 52). As an integrated part of some modern-day Peruvian subcultures, markets in
Peruvian cities like Casma and Trujillo have dedicated sections for selling San Pedro cacti (Jay, 2019).
As such, the tradition of ceremonial practice is continued into the present day, and according to
Schultes et al. (1992, p. 166f), may be used “to cure sickness, including alcoholism and insanity, for
divination, to undo love witchcraft, to counter all kinds of sorcery, and to ensure success in personal
ventures.” For similar reasons, San Pedro ceremonies are also held throughout European countries
such as the Netherlands, Poland, Austria, and Spain, as indicated by websites yielded from top google
search queries (for instance see Retreat.guru; Acsauhaya.com; madretierraamor.com). These ceremo-
nies are usually provided by local facilitators who have adapted their own method of guidance,
although often inspired by indigenous traditions (Scuro & Rodd, 2015). Surprisingly, even though
the history and ritualistic implementation of San Pedro has been studied by anthropologists and
ethnobotanists (Dobkin, 1968; Gottlieb, 1977; Heaven, 2010, 2012; Jay, 2019; Schultes et al., 1992), San
Pedro has received virtually no exclusive attention in psychological research.
Like other psychoactive cacti, San Pedro cacti contain many alkaloids, most prominent among
them is the psychotropic phenylethylamine Mescaline (Jones, 2005; Ogunbodede et al., 2010).
Mescaline belongs to the class of classical serotonergic psychedelics, whose best-known representatives
are LSD, Psilocybin and DMT (Nichols & Barker, 2016). Psychedelic substances can be hallucinogenic
and induce so-called altered states of consciousness (ASC), which are typified by changes in the
perception of sensory input, reality, sense of self, mood, thoughts, space, and time (Preller &
Vollenweider, 2016). Psychedelic-induced ASC may also lead to mystical-type experiences and dis-
solution of the ego, which may be perceived as transcendental, similar to “peak experiences” (Barrett &
Griffiths, 2017; Johnson et al., 2019). There is evidence that psychedelics administered during
psychotherapy yield promising results in the treatment of OCD, smoking cessation, alcohol abuse,
anxiety concerned with life threatening illness, PTSD, and treatment-resistant depression (Garcia-
Romeu et al., 2016). Even in healthy individuals who consume psychedelic substances, there is
evidence for positive mental effects (Elsey, 2017; Griffiths et al., 2011; Schmid & Liechti, 2018;
Uthaug et al., 2018; Van Oorsouw et al., 2021). Evidence for similar positive effects associated with
mescaline use is starting to mount (Agin-Liebes et al., 2021; Uthaug, Davis et al., 2021). The underlying
mechanisms are not yet fully understood, but it has been proposed that the temporary alterations in
consciousness, specifically the mystical-type experience, may be driving the therapeutic effects
(Garcia-Romeu et al., 2014; Johnson et al., 2019; Majić et al., 2015; Van Oorsouw et al., 2022).
Apart from any beneficial or pleasant connotations of ASC induced by psychedelics, a psychedelic
experience may also be challenging, due to for example intense bouts of negative affective and somatic
states, potentially leading to what is colloquially called a bad trip (Barrett et al., 2016; Bienemann et al.,
2020; Guthrie, 2021). Challenging experiences can have a traumatic impact and lead to enduring
mental illness symptoms, prompting users to seek therapeutic assistance (Carbonaro et al., 2016;
Rubin-Kahana et al., 2021). Support and guidance by psychedelic guides (i.e., ceremony facilitators,
such as shamans, ceremony leaders or guides) are therefore considered essential in helping partici-
pants navigate through personal crises that might surface and prevent the occurrence of prolonged
310 A. BOHN ET AL.
negative states and adverse mental health effects post-experience (Bravo & Grob, 1989; Winkelman,
2007). In addition to the support provided by the ceremonial framework (or setting) also the mind-set
(i.e., set) of an individual (e.g., personality, history of negative life events, and current mood) is
believed to play a central role in the psychedelic experience (Carhart-Harris et al., 2018; Hartogsohn,
2017; Studerus et al., 2011). While the psychedelic guides are part of and shape the setting of the
psychedelic experience, they may also influence the set of the participant through mentally preparing
them for the experience. As psychedelics are explored for their auxiliary potential to psychotherapy
(Davis et al., 2021; Doss et al., 2021; Garcia-Romeu et al., 2016), it is of importance to gain insight to
which degree positive and negative experiences are mutually exclusive, and whether certain features of
a psychedelic experience could be associated with adverse reactions. Therefore, the current study will
include measurements of self-reported adverse reactions during ceremonial consumption of San
Pedro and will investigate whether certain induced mental states are associated with adverse reactions.
Although mescaline, has similar identifiable psychological effects as other classical psychedelics
such as psilocybin, LSD and DMT (Nichols & Barker, 2016), there is evidence that different psyche-
delic drugs induce different physiological responses (Holze et al., 2022; Isbell, 1959), and possibly
different ASC (Hirschfeld & Schmidt, 2020; Studerus et al., 2010). While the psychedelic effects in
humans are primarily mediated via 5-HT2A receptors (Holze et al., 2021; Preller et al., 2017;
Vollenweider et al., 1998), different psychedelic substances show additional unique receptor-binding
profiles (Ray & Manzoni, 2010; Rickli et al., 2016; Zamberlan et al., 2018). Mescaline, for instance, has
been found to also act on 5HT2C receptors, as well as on adrenergic, cholinergic, and dopaminergic
neurotransmitter systems (Cassels & Sáez-Briones, 2018; Dinis-Oliveira et al., 2019; Kovacic &
Somanathan, 2009; Nichols, 2004; Trulson et al., 1983). The effects of mescaline typically range
between 8 and 12 hours (Uthaug, Davis et al., 2021) and are therefore longer lasting than tryptamines
such as Psilocybin and (5-MEO-)DMT (Araújo et al., 2015). Differential pharmacological properties of
mescaline may support anecdotal user reports claiming unique subjective effects of mescaline in
a supposedly more gentle, euphoric, and bodily/tactile experience (Erowid, n.d; .; PsychonautWiki,
n.d.; Sociodelic, 2017), some even reporting it to be a more social psychedelic due to the induction of
a sense of confidence, extroversion, and eagerness to talk (Guttmann, 1936; Tripsitter, 2021). While
there are several other mescaline containing cacti like Peyote and the Peruvian Torch, San Pedro has
the highest mescaline content of up to 5% (Ogunbodede et al., 2010) and the most common form of
mescaline consumption (Uthaug, Davis et al., 2021). Furthermore, there is evidence for more
(psychoactive) alkaloids in San Pedro, such as tyramine, hordenine, 3−methoxytyramine, lophophine,
lobivine, MDPEA, and DMPEA (Bruhn et al., 2008; Gottlieb, 1977), some of which are known to
interact with the function of dopamine (Khan & Nawaz, 2016; Miller, 2011; Sotnikova et al., 2010),
adrenaline and noradrenaline (Hapke & Strathmann, 1995), and as such could potentially impact
various mental functions (Iversen & Iversen, 2007; Wise, 2004). Conversely, through the catechola-
minergic activity of both mescaline and other alkaloids, San Pedro may also induce a range of so-called
sympathomimetic effects that are typical of phenethylamines, including agitation, alertness, increased
heart rate and respiration, and talkativeness (Winstock et al., 2011). Lophophine, lobivine and
MDPEA are psychoactive phenethylamines with entactogenic effects (Bruhn et al., 2008) and
DMPEA is an inhibitor of monoamine oxidase (Keller & Ferguson, 1977), known to affect mood
(Akindele et al., 1970). San Pedro’s additional psychoactive alkaloids may explain why anecdotal user
reports even claim subjective differences between mescaline-containing cacti (Sociodelic, 2017;
Turner, 1994; Zamnesia, n.d.). However, beyond suggestive evidence from neurochemistry and
anecdotal reports, there is very little data available on the consciousness altering effects of San Pedro.
In sum, despite a long history of San Pedro use in South America and its recent spread to western
countries, there is little research on the effects of San Pedro consumption. The present study presents
an observative attempt at describing the consciousness altering effects of San Pedro. Detailing the
effects of San Pedro would inform both a large sample of users (Krebs & Johansen, 2013) about the
potential subjective and adverse effects of San Pedro in a ceremonial context, and guide future studies
interested in comparing subjective effects between psychedelics, which could ultimately benefit clinical
THE INTERNATIONAL JOURNAL FOR THE PSYCHOLOGY OF RELIGION 311
research that is investigating the potential benefits of different psychedelic substances (Johnson et al.,
2019).
In the current paper, we report the results of an observational study investigating the effects of
ceremonial San Pedro use. Our first aim was to investigate if ceremonial San Pedro consumption
induces ASC that differ significantly from what is considered normal waking (i.e. sober) conscious-
ness. Our second aim was to construct a consciousness profile of ceremonial San Pedro use, by
determining which of the San Pedro-induced ASC are comparable or different in terms of their
average relative strength (for instance, do users of San Pedro report stronger elementary imagery than
complex imagery?). Our third aim was to investigate which ASC are co-occurring (i.e. patterns of
correlations) during San Pedro-induced psychedelic experiences (for instance, if users of San Pedro
report strong experiences of elementary imagery, does this then come with stronger complex ima-
gery?). Given that San Pedro has a long history of consumption with the intent to induce mind-
altering effects, we expected that San Pedro would exert strong effects on human consciousness similar
to other classical psychedelics. With regard to the second and third aim, we had no specific expecta-
tions and analyzed the data to construct a consciousness profile of San Pedro in terms of strength and
co-occurrence of ASC.
Methods
Participants
Data were collected as part of a research project (including measurements at baseline, post-
ceremony and follow-up at 4 weeks) to investigate psychological and affect changes in association
with San Pedro consumption. For the current study only data describing experiences during the
ceremony (measured post-ceremony) were analyzed. Over a timespan ranging from July 2019 until
March 2020, we collected as many participants as possible who joined a San Pedro ceremony
provided by one of four organizations facilitating ceremonies throughout the Netherlands.
Participation was voluntary and no incentives were offered for joining the ceremony. Exclusion
criteria as implemented by the ceremony facilitators were psychopharmacological medication intake
(e.g. SSRI antidepressants or ADHD stimulants), psychopathological afflictions prone to psychotic
breaks or delusional thoughts (e.g. bi-polar disorder, schizophrenia or borderline personality
disorder), acute drug addiction (e.g. to cocaine or heroin), pregnancy, high or low blood pressure,
a history with epileptic seizures, allergic reactions to mescaline cacti, addiction, kidney or/and
intestine diseases and diabetes. Exclusion criteria as implemented by the researchers were non-
fluency in Dutch, and being less than 18 years of age. To incentivize finishing the follow-up
measurement, two 50-euro vouchers were raffled at the end of the follow-up survey. The study
was approved by the standing Ethics Review Committee Psychology and Neuroscience of Maastricht
University.
A total of 54 people signed up for the study of which 42 participants completed the post-ceremony
survey. As some participants skipped the baseline measurements, we collected demographic informa-
tion for 36 of 42 participants, that was evenly divided over 18 women (M.age = 44.78; range = 31–57;
SD = 8.66) and 18 men (M.age = 44.56; range = 32–64, SD = 9.5), all of whom were Dutch residents and
selected Europe as their place of origin. Looking at the attained educational degrees of the participants,
14% finished high school (n = 5), 17% got a vocational education degree (n = 6), 45% graduated from
a university of applied sciences (n = 16) and 25% obtained a university degree or higher (n = 9). 22%
reported to be struggling with affective problems (n = 8; i.e. symptoms of depression or/and anxiety).
As for reasons to participate, 19% indicated “Solving problems” (n = 7) as their main motivation, while
61% reported “Insight into oneself” (n = 22) and 19% reported “Other reasons” (n = 7). Furthermore,
94% had previous experience with entheogens (n = 34), of which 11% had exclusively used some form
of marihuana (n = 4), while the remaining people had previously used classical psychedelics at least
once. Lastly, 67% of the participants reported having no previous experience with San Pedro (n = 24),
312 A. BOHN ET AL.
compared to 33% who acknowledged having used San Pedro on a previous occasion (n = 12; range =
1–52, median = 1).
Study procedure
Participants first, independently of this study, signed up for a ceremony with one of four participating
organizations in the Netherlands that provide guided plant medicine (healing) ceremonies with San
Pedro. Subsequently, the organization presented participants with a recruitment letter from the
authors, inquiring whether they would, in addition to their ceremony, also like to participate in our
study. Upon agreement, interested participants allowed organizations to transfer contact information
to the researchers. Consequently, 7 days prior to the ceremony, participants meeting the inclusion
criteria were sent a letter of invitation, including a briefing on the goals and methods of this study, and
a link to the baseline survey inquiring, among others, about the previously detailed demographics
(duration approx. 10 min). Before all surveys, participants were asked informed consent for anon-
ymous collection, processing, and storage of the provided data. Directly after the ceremony, partici-
pants received a link to the post-ceremony survey containing a test-battery (see section Materials)
inquiring, among others, on their experiences during the ceremony (duration approx. 10–20 min).
Participants were instructed to fill in the post-ceremony survey as soon as possible, preferably within
a 24 h time frame. Debriefing followed after successfully finishing the follow-up measurement at 4
weeks. The set-up of the ceremonies differed between organizations, and sometimes per session (see
Ceremonial context). The researchers were not involved in the organization of the San Pedro
ceremonies.
Materials
Survey data was collected via the online Qualtrics platform (https://www.qualtrics.com). Demographic
and background information, as detailed in the participants section, were collected on age, sex,
continent of origin, education, previous experience with San Pedro and/or other hallucinogenic
substances (including marijuana), motivation for ceremony participation and current psychopatho-
logical afflictions. Four psychometric scales were used to explore the effects of San Pedro on human
consciousness. Detailed information for each scale is presented in the next paragraphs. All scales were
translated from the original English versions to non-validated Dutch versions. Translations were done
by one author and double-checked by another author. Scale reliability of each scale was checked by
calculating the internal consistency (i.e. Cronbach’s alpha or α). For all scales, items are added to
a mean total and subscale scores.
The Altered States of Consciousness Rating Scale (11D-ASC)
The 11D-ASC is a 42-item questionnaire investigating alterations in consciousness via 11 subscales.
The 11D-ASC is a revised questionnaire which originated in the 5D-ASC (94-items; Dittrich, 1998),
and reached its current form after revalidating research using substances with psychedelic properties
by Studerus et al. (2010). Items contain statements (e.g. “I felt I was in a wonderful other world”),
which can be answered on a continuous scale ranging from “No, not more than usually” (0) to “Yes,
much more than usually” (100), where 0 is considered to resemble a sober state. The internal
consistency of the subscales ranged from sufficient to excellent: Unity (5 items; α = .90), Spirituality
(2 items; α = .88 after removal of 1 of 3 items belong to the scale was, in hindsight, found to incorrectly
translated), Blissfulness (3 items; α = .83), Insightfulness (3 items; α = .64), Disembodiment (3 items; α
= .82), Impaired control and cognition (7 items; α = .85), Anxiety (6 items; α = .77), Complex Imagery
(3 items; α = .76), Elementary Imagery (3 items; α = .85), Audio-visual synesthesia (3 items; α = .87)
and Changed Meaning of Percepts (3 items; α = .68).
THE INTERNATIONAL JOURNAL FOR THE PSYCHOLOGY OF RELIGION 313
The Ego-Dissolution Inventory (EDI)
The EDI (Nour et al., 2016) is an 8-item questionnaire, which investigates ego-dissolution, a key
characteristic of peak experiences. Items contain statements (e.g. “I experienced a dissolution of my
’self’ or ‘ego’”) that can be answered on a continuous scale ranging from “No, not more than usually”
(1) to “Yes, I experience this completely/entirely” (100). The internal consistency was excellent
(α = .90).
The Challenging Experience Questionnaire (CEQ)
The CEQ by Barrett et al. (2016) is a 26-item questionnaire, consisting of a main scale and 7 subscales,
which investigates whether an experience was perceived as challenging, as a measure of adverse
reactions toward psychedelics, both in affect and cognition. Items contain statements (e.g. “Isolation
and loneliness”) that can be answered on a six-point Likert scale ranging from “None; not at all” (0) to
“Extreme (more than any other time in my life)” (5). Challenging experience scores were calculated
according to the instructions, by dividing the aggregated score of all items by 125 (e.g. the sum score
that would be obtained if all items were answered with “Extreme”). Subscales were calculated similarly,
by dividing the obtained score by the maximum score. The internal consistency of the (sub)scales was
excellent: Challenging experience (25 items; α = .96; 1 item was not included in the survey due to
a programming mistake), Grief (6 items; α = .90), Fear (4 items; α = .90; missing item belonged also to
this subscale), Death (2 items; α = .91), Insanity (3 items; α = .74), Isolation (3 items; α = .82), Physical
distress (5 items; α = .85), Paranoia (2 items; α = .90).
The Mystical Experience Questionnaire (MEQ)
The MEQ (MacLean et al., 2012) is a 30-item questionnaire, consisting of a main scale and four
subscales. The main scale investigates the occurrence of a mystical-type experience, an important
predictor that is hypothesized to be one of the responsible mechanisms for the clinical outcomes of
psychedelics (Yaden & Griffiths, 2020). Items contain statements (e.g. “Experience of oneness or unity
with objects and/or persons perceived in your surroundings”), which can be answered on a six-point
Likert scale ranging from “None; not at all” (0) to “Extreme (more than any other time in my life)” (5).
Mystical Experiences were calculated according to the instructions, by dividing the aggregated score of
all items by 30, so that the sum scores can be interpreted on the original scale. Subscales were
calculated similarly, by dividing the obtained score by the number of items in the scale. The internal
consistency of the (sub)scales was excellent: Mystical Experience (30 items; α = .97), Mysticality (15
items; α = .96), Positive mood (6 items; α = .91), Transcendence of time and space (6 items; α = .90)
and Ineffability (3 items; α = .87).
Ceremonial context
The following information was not systematically collected and is based on personal observations of
one of the researchers who visited multiple data collection sites (2019–2021). The set-up of the
ceremonies (e.g. location, group size, presence and style of music, rituals, preparatory activities etc.)
and the proceedings (screenings, briefings, instructions, preparatory recommendations, etc.) varied
over the participating organizations, but could also differ within organizations. We nevertheless
deemed an elaborate and detailed description of the context in which San Pedro was consumed
relevant. Firstly, to convey a better understanding of what constitutes a San Pedro ceremony. Secondly,
to provide insight into how different factors within and surrounding that what is considered
a ceremony could be at play.
The four participating organizations facilitated recruitment, including precautionary screening,
and a supportive ceremonial setting within a safe and restricted indoor or outdoor area. All partici-
pants were screened before participating, as they were required to fill in questionnaires provided by the
organization, inquiring, among others, on previous and/or acute mental health issues, medical
conditions, and reasons for participating. Facilitators were allied with medical experts (e.g., general
314 A. BOHN ET AL.
practitioner) to consult on potential contraindications hazardous to physical and/or mental well-
being, as to ensure safety of the participants.
In the weeks and days prior to the ceremony, participants were recommended to prepare for the
psychedelic journey by restricting diet (e.g. fasting, vegan diets, minimizing consumption of processed
food, or salt and sugar intake) and refraining from sex, digital media (e.g., television, social media, web
browsing) and drug consumption (incl. alcohol and certain psychopharmacological medication), and
to engage more in reclusive activities such as reading, walking in nature and meditation.
Each organization had its own way of preparing San Pedro, varying from boiling dried San Pedro
chips with water into a concoction, offering powdered San Pedro on the spot to be mixed with apple
juice or by cooking the meat of fresh cacti into a liquid substance. Dosages were determined by the
ceremony leader and varied per person; often initial dosages were equal among all participants, but as
the ceremony went along the leader offered voluntary additional dosages as deemed adequate. Initial
effects were noticeable after 1 to 2 hours, although this may have varied per participant. The complete
length of intoxication varied between 10 and 17 hours, depending on consumption of additional doses.
Organizations were represented at the ceremony through teams consisting of a ceremony leader
and one or more guides, depending on the number of participants in the ceremony. Group sizes
ranged from 7 to 20 people. During the ceremony the organizations took care of comfort (e.g.,
comfortable chairs/couches), entertainment (e.g., recorded, or live music, including instruments to
be played with), guidance (e.g., emotional support), food (e.g., fruit, nuts, chocolate) and beverages
(tea and water). Additionally, some organizations also offered people to participate in shamanic rituals
during the ceremony, such as smoking the Mapacho tobacco leaf (see Sharrock, 2018) or ritualized
blowing of Rapé snu (Stanfill et al., 2015) up the nostril cavities, which can supposedly help people
move forward from difficult phases in their psychedelic journey. All organizations set up a fire in a pit
or stove and an altar in the middle of the ceremonial space, containing shamanic ornaments (e.g.,
rattles, feathers, incense) and items with spiritual and/or sacramental meaning (e.g., incense, candles,
mineral stones). Participants could also position meaningful personal items (e.g., a picture of a loved
one) at the altar.
Directly before San Pedro servings were shared, some ceremony leaders described the effects of San
Pedro, and the energy of San Pedro as The Grandfather, a masculine energy that may include animal
spirits, such as the Spirit of the Jaguar, the Kolibri and the Condor. In terms of physical effects,
ceremony leaders indicated that San Pedro generally (but not always) allows the user to be more active,
physically, and socially, through engaging in, for example, dance, talks and music making, as
compared to other psychedelics. Moreover, the ceremony leaders claimed that the intensity of effects
of San Pedro comes in waves slightly digressing over time, accordingly, giving the impression at times
that one is sobering up and the most significant part of the experience has waned, whereas in fact
psychedelic effects may resurface, drawing people back into intense alterations of consciousness.
Furthermore, the ceremony leaders noted that some adverse effects could come up, such as nausea,
vomiting (purging), tremors, heart palpitations, sweating, headaches, and sudden bouts of feeling very
cold or warm. They also warned that at the end of the ceremony while the effects of San Pedro are
wearing off, sleeping could be difficult, because of restlessness, anxiety, visual hallucinations, or intense
dreaming. Participants were also told that they might experience slight headaches during this period.
Data-analysis
First, to investigate our aims, we aggregated the data for all four questionnaires into the according
subscales. Four CEQ item responses were missing and accounted for in the average subscale scores of
the respective participants. No other missing values were present in the data set.
To investigate the first aim, whether ceremonial San Pedro consumption induces ASC that differ
significantly from normal waking consciousness, we conducted one sample t-tests for the subscales of
the 11D-ASC and EDI to test whether they differ from 0, as both questionnaires assume 0 to be the
sober state. We did not include CEQ and MEQ values here, as the phrasing of these questions did not
THE INTERNATIONAL JOURNAL FOR THE PSYCHOLOGY OF RELIGION 315
ask participants to compare it against a sober state. Then, to answer our second aim, to construct
a consciousness profile of San Pedro-induced ASC, we ran an ANOVA to compare the scores of the
11D-ASC subscales by pairwise comparison and applied Bonferroni adjustments to correct the
p-values for multiple comparisons. We included the EDI in this analysis, as it utilizes the same
range of scores as the 11D-ASC. Similar separate analyses were run for the CEQ and MEQ scores.
Finally, to answer our third aim to determine which ASC co-occur during San Pedro-induced
psychedelic experiences, we conducted a correlation analysis including sum scores of ASC, EDI,
CEQ and MEQ subscales using pairwise complete observations and calculated Pearson’s correlation
coefficients, also with a Bonferroni correction applied for multiple comparisons. Subsequently, the
correlations were visualized via a matrix using the corrplot function (version 0.90; Wei & Simko, 2021)
in R (version 4.1.1; R Core Team, 2020) and via a Network Analysis using MATLAB’s graph function
in MATLAB R2017a (MATLAB, 2017). The matrix plot allows identifying significance and magnitude
and orders the variables in rows and columns based upon hierarchical clustering. The network analysis
plots graphs with undirected edges, and graphically groups them based on a matrix of significant
correlations. The network analysis visualizes the significant correlations between subscales as solid
lines connecting scales and spatially arranges scales based on the pattern of correlations between each
individual scale and all other scales. Scales that have the largest number of significant correlations with
other scales are placed centrally in the cluster. A cluster refers to a group of points in the network
analysis graph that is connected in the form of a network structure. These clusters do not necessarily
indicate a causal network, as is sometimes the case in genetics or clinical psychology (Borsboom &
Cramer, 2013), but reflect a measure of interrelations between the different subscales that were used to
describe the San Pedro experience.
Results
The eect of San Pedro on human consciousness
To answer our first aim, whether ceremonial San Pedro consumption induces ASC that differ
significantly from normal waking consciousness, we report the results of one sample t-tests for the
11D-ASC and the EDI. Furthermore, we report the descriptives of the MEQ, and CEQ.
11D-ASC
All mean scores on the 11 subscales of the 11D-ASC differed significantly from zero (See Table 1),
which indicates that participants experienced ASC for each of the 11 dimensions included in the 11D-
ASC questionnaire (see Figure 1).
Table 1. Descriptive information and results of one-sample t-test of the 11D-ASC and EDI (N = 42).
Scale M SD t-value p-value* skew.se2** Min-max
11D-ASC
Experience of unity 53.64 31.07 11.19 <.001 −.05 1-100
Spiritual experience 63.13 33.00 12.40 <.001 −.93 1.5-100
Blissful state 50.98 30.03 11.00 <.001 −.36 0–99.6
Insightfulness 51.72 26.06 12.86 <.001 −.30 1-100
Disembodiment 22.60 24.19 6.05 <.001 1.20 0–76.33
Impaired Control and Cognition 21.83 20.43 6.92 <.001 1.45 0-80
Anxiety 10.86 13.99 5.03 <.001 2.63 0–56.67
Complex Imagery 45.24 30.95 9.47 <.001 .24 0-100
Elementary Imagery 43.75 33.86 8.38 <.001 .09 0-100
Audio-visual synesthesia 36.69 32.56 7.30 <.001 .60 0–96.67
Changed meaning of percepts 45.94 28.44 10.47 <.001 −.79 1-100
Ego-dissolution Inventory 47.85 26.17 11.85 <.001 −.77 2.38–98.62
* This p-value displays the significant difference from zero, obtained by a one-sample t-test.
** skew.2se values above 1 or below −1 signify abnormality of the distribution due to outliers.
The table presents an overview of the results from one-sample t-tests, including means (M), standard deviations (SD), t-values,
significance values (p-value), skewness of distribution (skew.se2), minimum and maximum obtained values (Min-Max). In Table S1
(see supplementary online materials), we report the data of the 11D-ASC scale in a different format, namely the 5D-ASC and 3D-
OAV scales that collapse the information in the 11D-ASC in five and three factors, respectively.
316 A. BOHN ET AL.
EDI
Participants’ average scores on the EDI were found to be significantly different from zero (see Table 1),
indicating that participants’ self-reported level of ego-dissolution during the ceremony was signifi-
cantly higher than during normal waking consciousness. On average, the San Pedro experience
appears to be characterized by a medium level of ego-dissolution (M = 47.85, SD = 26.17).
MEQ
Twenty-six Participants (62% of the total sample) were classified with a “complete mystical experi-
ence,” by having a total score higher than 3.0 (60% of the maximum score; cf. Griffiths et al., 2006). See
Table 2 for the descriptive information on the MEQ scores and the CEQ scores.
Figure 1. Altered states of consciousness as measured with the 11D-ASC and EDI associated with ceremonial San Pedro use.
Horizontal bar chart of mean scores of the 11D-ASC subscales and EDI scale revealing significant differences from the sober state (first
study aim; all 11D-ASC subscales and the EDI were statistically different from 0, i.e. the sober state) and the consciousness profile of
ceremonial San Pedro use (second study aim; see the main text for the statistical differences between subscales). Error bars indicate
the 95% confidence interval. Figure S1 in the online supplementary materials displays a radar chart of the same 11D-ASC subscales
without Ego-dissolution. Radar graphs have been used in other research on ASC and allow for quick visual comparison between
different substances.
Table 2. Descriptive information of the MEQ and the CEQ (N = 42).
Scale M SD skew.2se* Min-Max
Challenging Experience Questionnaire .20 .19 2.32 0-.90
Fear .15 .23 2.70 0-1
Grief .29 .26 1.42 0-1
Physical distress .28 .23 1.21 0-.92
Insanity .11 .18 3.25 0-.87
Isolation .16 .20 2.05 0-.087
Death .10 .24 3.51 0-1
Paranoia .08 .18 3.82 0-.8
Mystical Experience Questionnaire 3.15 1.14 −.87 .23-4.8
Mystical 3.29 1.25 −1.18 0-5
Positive mood 3.25 .126 −1.15 0-5
Transcendence of space and time 2.58 1.31 .066 0.5-5
Ineffability 3.37 1.29 −.917 0-5
* skew.2se values above 1 or below −1 signify abnormality of the distribution due to outliers
The table presents an overview of the descriptive information from the Challenging Experience Questionnaire and
Mystical Experience Questionnaire, including means (M), standard deviations (SD), skewness of distribution
(skew.2se), minimum and maximum obtained values (Min-Max).
THE INTERNATIONAL JOURNAL FOR THE PSYCHOLOGY OF RELIGION 317
CEQ
San Pedro evoked a relatively low overall rating of “challenging experience,” when taking the mean
score and the maximum scale scores in consideration. Furthermore, on a participant level, four
participants had scores that indicated a slight to moderately “challenging experience.” Moreover,
one participant had a moderate to strong challenging experience, and one participant was found to
have experienced a strong to extremely challenging experience (see Figure S3).
Constructing a consciousness prole of San Pedro induced ASC
Our second aim was to construct a consciousness profile of San Pedro-induced ASC, via within-
subjects ANOVA Bonferroni corrected pairwise comparisons of the scores on the 11D-ASC subscales.
11D-ASC and EDI
Within-subjects ANOVA (F(11, 31) = 10.156, p < .001, η
p2
= .783) indicated that there were significant
differences among the ASC subscales and the EDI. Subsequent pairwise comparisons are presented in
supplementary Table S3. Participants’ scores were highest for Spiritual experience (above 63), see
Figure 1. A group of subscales with medium scores (between 43 and 54) was found to include
Experience of unity, Blissful state, Insightfulness, Complex imagery, Elementary imagery, Changed
meaning of percepts and Ego-dissolution. Scores on these latter subscales were not statistically different
from each other. Scores on Spiritual experiences however differed from a selection of subscales in this
latter group, in particular Complex imagery and Changed meaning of percepts. A second group of
subscales with low scores (ranging between 10 and 23) was found including Disembodiment, Impaired
control and cognition and Anxiety. Scores on the subscales in this latter group were found to differ
statistically from all subscales in the previously described group with medium scores. Within the group
with low scores, Anxiety was scored significantly lower than Impaired control and cognition. Finally,
scores on the Audio-visual Synesthesia subscale (37) were found to be somewhere in between the two
groups. Audio-visual synesthesia scores were significantly higher than all subscales in the group with
low scores, but significantly lower than a selection of subscales in the group with medium scores, in
particular Experience of Unity and Insightfulness.
MEQ
Repeated-measures ANOVA (F (3, 39) = 7.786, p < .001, η
p2
= .375) indicated that there were signifi-
cant differences between the four MEQ subscales. Pairwise comparisons are presented in supplemen-
tary Table S3. Transcendence in time and space was found to be significantly different from all other
scales, but no further differences between pairs of scales were found to be significant.
CEQ
Repeated-measures ANOVA (F (6, 36) = 11.603, p < .001, η
p2
= .659) indicated significant differences
between the 7 subscales of the CEQ. Pairwise comparisons between CEQ subscales are presented in
supplementary Table S4. Grief and Physical distress were most pronounced and significantly different
from the rest, but not from each other. Fear, Insanity, Isolation, Death and Paranoia were not
significantly different from each other.
Co-occurrence of ASC during San Pedro-induced psychedelic experiences
Our third aim was to determine which ASC are co-occurring during San Pedro-induced psychedelic
experiences. To this end we constructed a correlation matrix including all correlations between
subscales and conducted a Network Analysis. In both analyses we identified two clearly separate
clusters in the San Pedro Experience (see Figures 2 and S3). The first cluster consisted of the four
subscales of the Mystical Experience Questionnaire (Mysticality; Positive mood; Transcendence of time
and space; Ineability), the EDI, and several ASC subscales (Experience of unity, Spirituality,
318 A. BOHN ET AL.
Blissfulness, Insightfulness, Disembodiment, Elementary imagery, Audio-visual synesthesia, Complex
imagery and Changed meaning of percepts). The other cluster consisted of all CEQ subscales and
a selection of ASC subscales (Anxiety, Impaired control and cognition). There were no significant
correlations between nodes in the separate clusters following correction for multiple comparisons.
Discussion
The current study investigated the effects of ceremonial San Pedro use on participants’ self-reported
states of consciousness as reflected in 11 dimensions of ASC, ego-dissolution, mystical experiences,
and challenging experiences. In the consecutive discussion, we will first discuss the results of the
analyses for each of the three successive aims. Subsequently, we will discuss the potential influence of
the ceremonial setting, and limitations and directions for future research, before reaching
a conclusion.
The eect of San Pedro on human consciousness
The first aim of this study was to investigate whether consumption of San Pedro induces any changes
in consciousness beyond normal waking consciousness as measured with the four instruments, 11D-
ASC, EDI, MEQ and CEQ.
11D-ASC
Results showed that all 11D-ASC subscales differed from zero, indicating that participants’ self-
reported state of consciousness was significantly altered following ceremonial San Pedro use
and clearly distinct from the sober state. This finding suggests that ceremonial San Pedro use
Figure 2. Network analysis graph. The graphical result of the network analysis. Each node represents either a subscale or total score
of our measurements (Red = 11D-ASC, yellow = EDI, green = MEQ, blue = CEQ). Lines represent significant correlations corrected for
multiple comparisons. No information can be deduced from distance and angle between two nodes. For further explanation see
method and result section. Some variables were abbreviated among the 11D-ASC (Unity = Feelings of Unity; Spiritual = Spiritual
Experience; Blissful = Blissful state; Insight. = Insightfulness; Disembod. = Disembodiment; Impair. = Impaired control and cognition;
Elementary = Elementary Imagery; Complex = Complex Imagery; Synesthesia = Audio-visual synesthesia; Change = Changed
meaning of percepts) and the MEQ (Positive = Positive Mood; Transcendence = Transcendence in time and space) and the CEQ
(Distress = Physical distress).
THE INTERNATIONAL JOURNAL FOR THE PSYCHOLOGY OF RELIGION 319
tends to affect users’ consciousness in a broad manner, by impacting multiple phenomenolo-
gical aspects of consciousness. This property is shared by many psychedelics (Carhart-Harris
et al., 2016; Holze et al., 2021, 2022; Liechti et al., 2017; Studerus et al., 2010) and supports the
classification of San Pedro as a psychedelic plant. It should be noted, however, that the current
observational study design does not allow us to separate the influence of the ceremony from
the consciousness altering effects (see The potential inuence of the ceremonial setting for
a more extensive discussion).
EDI
Ego-dissolution was significantly different from zero in a one sample t-test, indicating that the
ceremonial San Pedro experience was characterized by a state of ego-dissolution that differs from
the normal, sober state of mind in most participants. Comparable findings were reported by Uthaug,
Davis et al. (2021; M = 48; SD = 26)
1
in a large-scale retrospective survey study (N = 452) investigating
naturalistic use of mescaline, including (but not limited to), ceremonial San Pedro consumption. The
findings on the EDI further corroborate the classification of San Pedro as a psychedelic substance and
suggest that San Pedro presents no exception to the close relationship that has been noted between the
consumption of psychedelics and the state of ego-dissolution (Barrett & Griffiths, 2017; Letheby &
Gerrans, 2017; Nour et al., 2016). Again, it should be noted that these conclusions require further
confirmation by experimental studies that control for the possible influence of the ceremonial setting.
MEQ
Analysis of the MEQ indicated that roughly two out of three participants (62%) satisfied the criteria for
a complete mystical experience (60% of the total score), demonstrating the mystical character of a San
Pedro experience in a ceremonial setting. Of interest to note, although bound to the same limitations
as mentioned in the previous two paragraphs, Uthaug, Davis et al. (2021) also reported near similar
results for mescaline and San Pedro (M = 3.2 SD = 1.1), corroborating the potency of (ceremonial) San
Pedro use to induce a complete mystical experience.
CEQ
We also investigated to what degree the ceremonial consumption of San Pedro evokes challenging
experiences. Our findings suggested relatively low levels of challenging experiences for the average
participant in the current study, as the mean value of .20 (SD = .19) represents an average response of
“so slight I cannot decide” across all items included in the CEQ questionnaire. At the level of
individual participants, we found that two out of 42 participants felt more than moderately challenged
during the San Pedro ceremony, with one participant scoring between “moderate” and “strong” on the
CEQ, and another participant scoring between “strong” and “extreme (more than ever before in my
life)”. These findings suggest that for most participants (95%) in the current sample the San Pedro
experience was not particularly challenging, but that a small percentage of participants experienced
moderate to extreme negative effects. Uthaug, Davis et al. (2021) also included measures of challenging
experiences for mescaline in general (M = 0.12; SD = 0.12) and for San Pedro specifically (M = 0.14;
SD = 0.14).
2
The current results further add to the evidence that mescaline consumption (here in the
form of San Pedro, in the context of a ceremony) entails a low prevalence of challenging experiences.
Although the current observational findings are subject to various limitations, the results discussed
above provide first tentative evidence that San Pedro used in the context of a ceremony induces
widespread altered states of consciousness, ego-dissolution, and mystical states, at levels comparable
with other mescaline containing psychedelics (e.g. Uthaug, Davis et al., 2021). Furthermore, like other
psychedelics (Carbonaro et al., 2016; Schlag et al., 2022), a small proportion of participants report
negative emotional experiences to be part of San Pedro’s consciousness altering effect.
1
Adjusted for scale differences.
2
Adjusted for scale differences.
320 A. BOHN ET AL.
A consciousness prole of the San Pedro experience
The second aim of this study was to construct a consciousness profile of the San Pedro experience by
quantifying and comparing the average scores across subscales of the 11D-ASC and EDI, as well as the
MEQ and CEQ.
11D-ASC and EDI
The dimension of the 11D-ASC that was most strongly altered was Spiritual experience. In agreement
with this finding, archeological records from the Andes region (Carod-Artal & Vazquez-Cabrera,
2006; Samorini, 2019; Torres, 1995), suggest that San Pedro may have functioned as a historical
catalyst among the native inhabitants of Peru, effectuating the start of institutionalized religious
worship of deities (De Rios, 1977; Glass-Coffin, 2010; Millière et al., 2018). Today’s users of psyche-
delics also seem more likely to develop spiritual interests following mystical experiences induced by
psychedelics (Aday et al., 2020; Móró et al., 2011). However, it should be considered that the current
findings were obtained in the context of a ceremonial setting, which included various spiritual
elements (See Ceremonial context under Methods) that may have contributed to the relatively high
scores on the spirituality dimension of the 11D-ASC. In accordance with this view, research has found
that contextual factors such as set and setting, including individual expectations, intentions, and
preparations prior to psychedelic consumption, as well as the physical, social, and cultural setting in
which the consumption takes place, may exert strong influences on individual experiences accom-
panying drug consumption (Hartogsohn, 2016). This is supported by findings of Uthaug, Mason et al.
(2021) who did not find differences between their placebo and ayahuasca group in their reports of
Spiritual Experience, suggesting that the ceremonial setting induced part of the ASC.
Further, ceremonial San Pedro use appears to induce relatively little Anxiety, Disembodiment and
Impaired control and cognition. While low anxiety mirrors the low incidence of challenging experi-
ence, reports of low disembodiment and impaired control and cognition could reflect the sympatho-
mimetic effects that are characteristic of phenethylamines (Cassels & Sáez-Briones, 2018; Zamberlan
et al., 2018) and San Pedro’s adrenergic (Hapke & Strathmann, 1995) and entactogenic alkaloids
(Bruhn et al., 2008) that stimulate arousal and bodily activation. This hypothesis fits with the
observations that ceremony facilitators and attendees describe the San Pedro experience on multiple
occasions as a gentle, physically grounding and a down-to-earth experience. Dinis-Oliveira et al.
(2019, p. 190) report a comparable experience in a user who found him/herself “weighted down by
some strange gravitational force”. These observations are furthermore matched by websites that collect
and summarize user reports of various psychedelics (Microdosinginstitute, n.d.; PsychonautWiki, n.
d.) where the use of mescaline is associated with (a greater) emphasis on bodily and tactile sensations
and sense of control.
Finally, San Pedro users rated ego-dissolution at medium levels of intensity. It is worth noting that
ego-dissolution as a construct has been suggested to be broader than a simple unidimensional concept,
as the loss of self-awareness can occur at multiple levels such as narrative self-loss, loss of body
ownership, loss of bodily awareness and loss of self-location (Barrett & Griffiths, 2017; Letheby &
Gerrans, 2017; Millière et al., 2018). Sympathetic nerve stimulation may therefore also constrain the
loss of bodily self-representations, which is interesting considering that other phenethylamines such as
MDMA and d-amphetamine have produced similar levels of ego-dissolution and disembodiment as
San Pedro (Holze et al., 2020). However, it must be noted that the reported values of ego-dissolution
following psychedelic consumption vary considerably between studies (Holze et al., 2020; Uthaug
et al., 2018; Van Oorsouw et al., 2021), and were found not to differ from a placebo in one study
(Uthaug, Mason et al., 2021). Thus, any comparison of ego-dissolution between substances should be
considered preliminary before investigated in future research by appropriate designs, including direct
comparisons among multiple substances, doses, and settings, to disentangle how sympathomimetic
effects may influence psychedelic-induced ego-dissolution.
THE INTERNATIONAL JOURNAL FOR THE PSYCHOLOGY OF RELIGION 321
MEQ
Among the factors of a Mystical Experience, Transcendence in time and space was scored significantly
lower than the factors Mystical, Positive mood and Ineability. On closer scrutiny, we separated the
items of the MEQ inquiring about time versus those inquiring about space. We found that in
particular Transcendence of space was scored significantly lower than the other factors included in
the MEQ. Considering that our experience of space depends on sensorimotor structures that are
involved in the construction of body awareness (Millière et al., 2018), lower scores on Transcendence of
space items may also be explained by the hypothesized sympathomimetic effects of San Pedro. More
specifically, heightened physical awareness associated with San Pedro may root one’s sense of presence
in the current physical environment, preventing spatial self-transcendence.
CEQ
The pairwise comparisons between the different challenging experiences suggested that for those partici-
pants who encountered a challenging experience following San Pedro consumption, Grief and Physical
distress were most prominent while Fear, Insanity, Isolation, Death, and Paranoia were less often reported.
The reason why grief may be relatively pronounced in our sample may have to do with the therapeutic
nature of the ceremonies and the way the ceremonial guides invite people to explore autobiographical
experiences involving loss and emotional pain to find relief and spiritual healing (Gorman et al., 2021;
Healy, 2021; Wolff, 2020). Although the other categories could similarly be featured in a therapeutic
process, the items that make up Grief comprise a larger range of potentially distressing experiences (i.e.,
sadness, grief, despair, crying and emotional suffering). The Grief measurement as such seems to cover
a greater portion of the negative human experience. The finding of relatively high Physical distress is
interesting in the light of relatively low disembodiment, as both might be related to the sympathomimetic
effects of some of San Pedro’s alkaloids. Hordenine, for instance, may increase heart rate and respiration
frequency (Dinis-Oliveira et al., 2019) and mescaline, as a phenylethylamine, is known for activating the
sympathetic nervous system through adrenergic and dopaminergic pathways (Kovacic & Somanathan,
2009). Activation of the sympathetic nervous system heightens bodily awareness and could thereby
enhance appraisal of physical reactions (Barile, 2019; Hoehn-Saric & McLeod, 1988; Schulz & Vögele,
2015).
Taken together, the consciousness profile of ceremonial San Pedro use seems to be character-
ized by relatively strong spiritual experiences, and low incidence of challenging experiences.
Furthermore, we hypothesize that our results of relatively low disembodiment, low transcen-
dence of space, medium ego-dissolution, a high retainment of control and cognition, and high
physical distress in case of (incidental) challenging experiences, may reflect activation of the
sympathetic nervous system that is known to accompany some of San Pedro’s alkaloids.
Co-occurrence of ASC during San Pedro-induced psychedelic experiences.
The third aim of this study was to investigate to what extent induced ASC were co-occurring during
the San Pedro ceremony. The resulting correlation matrix and network analysis revealed two clusters
of altered states:
The first cluster, graphically centered around ego-dissolution (see Figure 2), was interpreted to
represent desirable states that are often anticipated with the consumption of psychedelics (Olson et al.,
2020). The centering of the cluster around ego-dissolution suggests that ego-dissolution was strongly
associated with mystical experiences and desired altered states of consciousness during the ceremonial
use of San Pedro. The finding that ego-dissolution seems to play a central role in the San-Pedro
experience corroborates previous suggestions that ego-dissolution may be central to any psychedelic
or mystical experience (Barrett & Griffiths, 2017; Letheby & Gerrans, 2017; Nour et al., 2016).
Next to the positively valenced cluster, a second cluster was found, which appears to reflect
undesirable or unpleasant states evoked by ceremonial San Pedro use. Interestingly, the correlations
in this network seem to suggest that the experience of a negatively valenced state increases the
likelihood of experiencing more negative states. One possible way to look at this finding is that
322 A. BOHN ET AL.
individual differences in mood or affective valence during the ceremony may influence the type of
experiences that individuals encounter and report (Russell, 2003). Negative mood may profoundly
bias one’s attention, perception, autobiographical memory and processing of social stimuli (Phelps,
2006), and influence one’s judgment, reasoning, and decision making (Blanchette & Richards, 2010) in
a negative direction. In other words, individuals who are in a negative mood may interpret various
experiences during a ceremony more negatively. This may result in a downward spiral of negative
thoughts and feelings.
Interestingly, there was no significant negative correlation between any of the positive and negative
subscales across both clusters of the network analysis. It could have been the case, for instance, that the
more anxiety-inducing an experience was, the less blissful it would have been perceived. However, this
was not the case in our data. The separation between the two clusters (Figure 2) and a follow-up
analysis to map the relationship between the occurrence of mystical (MEQ) and challenging (CEQ)
experiences (see supplementary Figure S3) suggests that the two sides of the San Pedro experience, i.e.,
positively, and negatively valenced experiences, are not mutually exclusive in this sample. Future
research may investigate how positive and negative experiences are expressed over time, considering
that many psychedelic trips span over several hours.
The potential inuence of the ceremonial setting on the reported eects
Beyond the mentioned potential influences of the ceremonial setting on our results, there are several
additional factors that are worth considering. Especially the influence of the facilitator’s practicing
style and the structural properties of the ceremony, such as group size, interactions between partici-
pants and the preparatory and integrative activities surrounding the ceremony, deserve further
elaboration (Carhart-Harris et al., 2018; Hartogsohn, 2017; Winkelman, 2007).
As this study measured the ASC during naturalistic ceremonial San Pedro consumption, ASC
cannot solely be attributed to San Pedro but may additionally reflect influences of the ceremony on the
mind-set of the participant. Hartogsohn (2016) suggests that the set & setting may induce placebo ASC
and influence the psychedelic trip. Along the same lines, Olson et al. (2020) found that a small
percentage of participants reported profound ASC following consumption of a placebo psychedelic.
Furthermore, participants can experience ASC in religious, shamanic, or cultural ceremonies that do
not involve psychedelics, through purposefully participating in chanting, dancing or drumming (Jilek,
1982; Polito et al., 2010; Thomason, 2010). Additionally, fewer mystical experiences were found in
some controlled studies using an academic laboratory setting instead (Holze et al., 2022; Liechti et al.,
2017). Consequently, it is hard to distinguish the drug effects from the contextual effects in the
measurements of ASC as obtained by this study.
Likewise, previous research has found that ceremonial settings may have an influence on perceived
challenges, as administering psychedelics in a structured, supportive and safe setting induced higher
mystical experiences while generating lesser challenging experiences (Sepeda et al., 2020). Traditionally-
led ceremonies conducted within indigenous societies may build upon preserved old cultural knowledge to
reduce the risks and challenges associated with consumption of plant medicines (Fotiou, 2020). Such
properties include preparation and integration strategies (Dorsen et al., 2019), social belongingness in
group settings (Carhart-Harris et al., 2018; Kettner et al., 2021), and choice of music (Strickland et al., 2020).
Similarly, ceremonies in the current study were led by experienced facilitators who helped participants to
prepare their body and mind for the ceremony days in advance and supported participants in various ways
(e.g. guidance, rituals, music, atmosphere, safety) throughout the ceremony, which may have helped
participants to navigate through challenging phases and reach insights (e.g. Winkelman, 2007). More
recent qualitative work among ayahuasca ceremony attendants has also shown the importance of setting
elements, such as feeling comfortable in the group, leadership, and physical comfort, in helping to reduce
challenging experiences and increasing mystical experiences (Pontual et al., 2022). Future research should
further disentangle how the various elements of guided settings surrounding San Pedro use affect challen-
ging and mystical experiences.
THE INTERNATIONAL JOURNAL FOR THE PSYCHOLOGY OF RELIGION 323
Further, San Pedro ceremonies in this study consisted of varying group sizes and often multiple
guides. The effect of group size on the psychedelic ceremony plays partly into the experience of
communitas, which is defined as a sense of intense togetherness and shared humanity (Haidt et al.,
2008). Communitas has been shown to correlate with social connectedness and wellbeing after
psychedelic experiences (Kettner et al., 2021). Hence, considering the social nature of ritual ceremo-
nies (Watson-Jones & Legare, 2016), the social aspect of any ceremony and its effect on the subjective
experience of participants, must not be underestimated.
Further limitations & future directions
Beyond the limitations mentioned earlier, several additional limitations can be pointed out that are
concerned with the current observational study design. One limitation of the current study is that it did
not include a placebo control condition with which to compare the ASC that accompany ceremonial
San Pedro use. It should be noted though that the current study design asked participants to rate their
mental state during the San Pedro ceremony relative to their normal (i.e. sober) waking consciousness.
Other limitations of this study concern the sample size and the number of organizations included.
Considering that our study is the first to systematically map the ASC that accompany ceremonial San
Pedro use, replication in a larger sample and with a larger set of organizations is needed to draw more
definite conclusions about the consciousness altering effects of ceremonial San Pedro use. Next, our
results are limited by the fact that the dose (by bodyweight) of San Pedro consumed is unknown. The
amount of mescaline and other alkaloids may vary between two cacti (Ogunbodede et al., 2010), and
thus also between the brews and powders that were consumed throughout the ceremonies provided by
the various organizations. Moreover, the amount of a specific brew or powder that was consumed may
have varied across participants, as this was under the control of the facilitators and sometimes up to the
preference of the individual participant. Hence, the question remains how changes in consciousness that
accompany San Pedro consumption manifest when doses of mescaline and alkaloids are parametrically
controlled. Finally, not all ceremonies were exclusive in terms of drugs that were consumed, signaling
a potential entourage eect — the synergistic effect of polysubstance use on human consciousness
(Ribeiro, 2018). One practitioner offered participants the opportunity to smoke mapacho, a nicotine-
containing leaf which is used by some Amazonian tribes as a plant medicine in ceremonial context
(Sharrock, 2018), while two organizations allowed for the ingestion of cannabis in addition to San Pedro
when participants were familiar with the effects and had regularly used cannabis before. As cannabis is
a substance which by itself is sometimes used for spiritual purposes and reaching peak-experiences
(Ferrara, 2021; Johnstad, 2020), but may also cause states of intense negative affect comparable to
a challenging experience (Cohen et al., 2019; Farmer et al., 2019), it complicates the degree to which the
reported experiences and their relative frequencies may be attributable to San Pedro (Kuc et al., 2022),
or to additional psychoactive substances consumed in the ceremony or their interaction.
Conclusion
The present study explored the effects of San Pedro consumption in a ceremonial setting on
human consciousness. The findings summarized in this study include the following. First,
although the observational design of the present study comes with several clear limitations,
our findings suggest that the ceremonial use of San Pedro is associated with a broad set of
prominent changes in consciousness which are akin to classical psychedelics. Second, our
findings suggest that ceremonial San Pedro use is characterized by relatively high levels of
spiritual experience, moderate levels of insightfulness, bliss, feelings of unity, ego-dissolution,
changed meaning of percepts, complex and elementary imagery, and audio-visual integration,
and relatively low levels of disembodiment, impaired control and cognition and anxiety, as
compared to normal waking consciousness. Third, results indicated that positively valenced
ASC tended to co-occur with other positively valenced ASC and that similar co-occurrence
324 A. BOHN ET AL.
occurred for negative ASC. We hope that these findings and the discussion of the hypothesized
mechanisms will provide a starting point for future research on the physiology and psychology
of San Pedro ASC and will contribute to the development of safe therapeutic applications of San
Pedro in both ceremonial and clinical settings.
Acknowledgements
We would like to thank all participants and ceremony organizations who contributed to the present research.
Author contributions
Arne Bohn: Conceptualization, Formal analysis, Software, Writing – Original Draft, Writing – Review & Editing,
Visualization. Michiel Kiggen: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data
Curation, Writing – Original Draft, Writing – Review & Editing, Visualization. Malin Uthaug: Conceptualization,
Methodology, Writing – Review & Editing. Kim van Oorsouw: Conceptualization, Methodology, Writing – Review &
Editing. Johannes Ramaekers: Conceptualization, Writing – Review & Editing. Hein van Schie: Conceptualization,
Methodology, Writing – Original Draft, Writing – Review & Editing, Supervision.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
The research reported in this project was funded by the Radboud University Behavioural Science Institute (AB, MK, and
HTvS) and Maastricht University (MU, KvO, JR).
Data availability statement
All data, stimuli and analysis scripts belonging to this research are available through the APA repository in the Open
Science Framework via the following link: https://doi.org/10.5281/zenodo.1212328.
Open Scholarship
This article has earned the Center for Open Science badges for Open Data, Open Materials and Preregistered. The data
and materials are openly accessible at https://doi.org/10.5281/zenodo.1212328.
Ethical approval
The study was approved by the standing Ethics Review Committee Psychology and Neuroscience at Maastricht
University.
Informed consent from participants
Participants were asked informed consent for anonymous collection, processing, and storage of the provided data.
ORCID
Arne Bohn http://orcid.org/0000-0002-2599-3489
Michiel H. H. Kiggen http://orcid.org/0000-0003-0900-0157
THE INTERNATIONAL JOURNAL FOR THE PSYCHOLOGY OF RELIGION 325
Malin V. Uthaug http://orcid.org/0000-0001-7903-1325
Kim I. M. van Oorsouw http://orcid.org/0000-0001-9148-5282
Johannes G. Ramaekers http://orcid.org/0000-0003-4553-376X
Hein T. van Schie http://orcid.org/0000-0002-1149-5198
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