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ORIGINAL INVESTIGATION
Psilocybin can occasion mystical-type experiences
having substantial and sustained personal
meaning and spiritual significance
R. R. Griffiths &W. A. Richards &U. McCann &R. Jesse
Received: 20 January 2006 /Accepted: 27 May 2006
#Springer-Verlag 2006
Abstract
Rationale Although psilocybin has been used for centuries
for religious purposes, little is known scientifically about its
acute and persisting effects.
Objectives This double-blind study evaluated the acute and
longer-term psychological effects of a high dose of psilocy-
bin relative to a comparison compound administered under
comfortable, supportive conditions.
Materials and methods The participants were hallucinogen-
naïve adults reporting regular participation in religious or
spiritual activities. Two or three sessions were conducted at
2-month intervals. Thirty volunteers received orally admin-
istered psilocybin (30 mg/70 kg) and methylphenidate
hydrochloride (40 mg/70 kg) in counterbalanced order. To
obscure the study design, six additional volunteers received
methylphenidate in the first two sessions and unblinded
psilocybin in a third session. The 8-h sessions were con-
ducted individually. Volunteers were encouraged to close
their eyes and direct their attention inward. Study monitors
rated volunteers’behavior during sessions. Volunteers
completed questionnaires assessing drug effects and mys-
tical experience immediately after and 2 months after
sessions. Community observers rated changes in the
volunteer’s attitudes and behavior.
Results Psilocybin produced a range of acute perceptual
changes, subjective experiences, and labile moods including
anxiety. Psilocybin also increased measures of mystical
experience. At 2 months, the volunteers rated the psilocybin
experience as having substantial personal meaning and
spiritual significance and attributed to the experience sus-
tained positive changes in attitudes and behavior consistent
with changes rated by community observers.
Conclusions When administered under supportive condi-
tions, psilocybin occasioned experiences similar to sponta-
neously occurring mystical experiences. The ability to
occasion such experiences prospectively will allow rigorous
scientific investigations of their causes and consequences.
Keywords Anxiety .Psilocybin .Methylphenidate .
Hallucinogen .Entheogen .Mystical experience .Spiritual .
Religion .Humans
Introduction
Psilocybin, a naturally occurring tryptamine alkaloid with
actions mediated primarily at serotonin 5-HT
2A/C
receptor
sites, is the principal psychoactive component of a genus of
Psychopharmacology
DOI 10.1007/s00213-006-0457-5
Electronic Supplementary Material Supplementary material is
available for this article at http://dx.doi.org/10.1007/s00213-
006-0457-5 and is accessible for authorized users.
R. R. Griffiths (*):U. McCann
Department of Psychiatry and Behavioral Sciences,
Johns Hopkins University School of Medicine,
5510 Nathan Shock Drive,
Baltimore, MD 21224-6823, USA
e-mail: rgriff@jhmi.edu
R. R. Griffiths
Department of Neuroscience,
Johns Hopkins University School of Medicine,
5510 Nathan Shock Drive,
Baltimore, MD 21224-6823, USA
W. A. Richards
Johns Hopkins Bayview Medical Center,
2516 Talbot Road,
Baltimore, MD 21216-2032, USA
W. A. Richards :R. Jesse
Council on Spiritual Practices,
Box 460220, San Francisco, CA 94146-0220, USA
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mushrooms (Psilocybe) (Presti and Nichols 2004). Psilocy-
bin, in the form of these mushrooms, has been used for
centuries, possibly millennia, within some cultures in
structured manners for divinatory or religious purposes
(Wasson 1980; Stamets 1996; Metzner 2004). The psycho-
logical effects of psilocybin, which are similar to other
classical serotonergically mediated hallucinogens [lysergic
acid diethylamide (LSD), mescaline, and N,N-dimethyl-
tryptamine (DMT)], include significant alterations in
perceptual, cognitive, affective, volitional, and somates-
thetic functions, including visual and auditory sensory
changes, difficulty in thinking, mood fluctuations, and
dissociative phenomena (Isbell 1959; Wolbach et al. 1962;
Rosenberg et al. 1964).
Early clinical research with psilocybin in the 1950s and
early 1960s attempted to study the effects of psilocybin
without recognition of the powerful influences of set and
setting (e.g., Isbell 1959;Hollister1961;Malitzetal.1960;
Rinkel et al. 1960). Subsequent research, which included
more preparation and interpersonal support during the period
of drug action, found fewer adverse psychological effects,
such as panic reactions and paranoid episodes, and increased
reports of positively valued experiences (Leary et al. 1963;
Metzner et al. 1965;Pahnke1969). In response to the
epidemic of hallucinogen abuse that occurred in the 1960s,
clinical research with psilocybin and other hallucinogens
largely ceased and has resumed only recently. Notably,
Vollenweider and colleagues from Switzerland and Gouzoulis-
Mayfrank from Germany have reported a series of studies
that have characterized the acute subjective, physiological,
and perceptual effects of psilocybin (e.g., Vollenweider et al.
1998; Gouzoulis-Mayfrank et al. 1999; Hasler et al. 2004;
Carter et al. 2005).
In the present study, we sought to use rigorous double-
blind clinical pharmacology methods to evaluate both the
acute (7 h) and longer-term (2 months) mood-altering and
psychological effects of psilocybin (30 mg/70 kg) relative to
an active comparison compound (40 mg/70 kg methylphe-
nidate). The study was conducted with 36 well-educated,
hallucinogen-naïve volunteers.
Materials and methods
Participants
The participants were recruited from the local community
through flyers announcing a “study of states of conscious-
ness brought about by a naturally occurring psychoactive
substance used sacramentally in some cultures.”There were
135 individuals screened over the telephone and 54 were
further screened in person. The 36 study participants (14
males) were medically and psychiatrically healthy, without
histories of hallucinogen use, and without family histories of
schizophrenia or other psychotic disorders or bipolar I or II
disorder. The participants had an average age of 46 years
(range 24 to 64) and were well educated; 97% (35 volun-
teers) were college graduates and 56% (20 volunteers) had
post-graduate degrees. Eighty-three percent (30 volunteers)
were employed full time, with the remainder employed part
time. Fifty-three percent (19 volunteers) indicated affiliation
with a religious or spiritual community, such as a church,
synagogue, or meditation group. All 36 volunteers indicated
at least intermittent participation in religious or spiritual
activities such as religious services, prayer, meditation,
church choir, or educational or discussion groups, with
56% (20 volunteers) reporting daily activities and an
additional 39% (14 volunteers) reporting at least monthly
activities. The volunteers did not receive monetary compen-
sation for participation. Although most volunteers had very
busy personal and professional schedules, they were inter-
ested in the study and made participation a priority. Based on
interviews, their motivation for participation was curiosity
about the effects of psilocybin and the opportunity for
extensive self-reflection in the context of both the day-long
drug sessions and the meetings with the monitors that
occurred between sessions. The Institutional Review Board
of the Johns Hopkins University School of Medicine
approved the study, and all volunteers gave their informed
consent before participation.
Study design
The study compared psilocybin (30 mg/70 kg) and
methylphenidate hydrochloride (40 mg/70 kg) using a
double-blind between-group, crossover design that in-
volved two or three 8-h drug sessions conducted at 2-
month intervals. Thirty-six volunteers were randomly
assigned to receive either two sessions (N=30) or three
sessions (N=6). The group of 30 volunteers were then
randomly assigned to receive psilocybin or methylpheni-
date on the first session (15 per group), with the alternative
drug administered on the second session. The other six
volunteers received methylphenidate on the first two
sessions and unblinded psilocybin on the third session.
The purpose of this condition was primarily to obscure
the study design to the participants and monitors (see
“Expectancy”section), and data from the six participants
were not used in the statistical analyses; however, those
data were generally consistent with the results described in
this report. Outcome measures obtained throughout the
drug sessions included blood pressure and monitor ratings
of participant mood and behavior. At about 7 h after drug
ingestion (when the primary drug effects had subsided),
the participants completed several questionnaires designed
to assess various aspects of hallucinogen experience
Psychopharmacology
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(described below). The longitudinal measures assessed
before and 2 months after each drug session included
measures of psychiatric symptoms, personality measures,
quality of life, and lifetime mystical experiences. A 1-year
follow-up assessment is still underway.
Drug conditions
Psilocybin and methylphenidate were administered in iden-
tically appearing opaque, size 0 gelatin capsules with
approximately 180 ml water. The dose of psilocybin
(30 mg/70 kg) was selected as a high safe dose based on
non-blind (Malitz et al. 1960; Metzner et al. 1965; Leuner
1981) and blind (Pahnke 1963,1969) studies conducted with
hallucinogen-naïve individuals in the 1950s–1960s. The
methylphenidate dose (40 mg/70 kg) was selected for the
comparison condition because it is a high, discriminable but
safe dose, it has an onset and duration of subjective effects
similar to psilocybin, and it produces some subjective effects
(e.g., excitability, nervousness, and/or increased positive
mood) overlapping with those of psilocybin (Chait 1994;
Rush et al. 1998; Kollins et al. 1998).
Meetings with monitor before and after sessions
The primary monitor met with each participant on four
occasions before his or her first session (for 8 h total) and on
four occasions (for 4 h total) after each session. A major
purpose of the participant-monitor meetings was to develop
and maintain rapport and trust, which is believed to
minimize the risk of adverse reactions to psilocybin
(Metzner et al. 1965). During these meetings, the partici-
pant’s life history and current life circumstances were
reviewed. The preparation of participants by the monitors
explicitly included the monitor’s expectation that the drug
session experiences could increase personal awareness and
insight, however, avoided even mention of the criteria used
to assess mystical experiences. A male clinical psychologist
(W.R.) with extensive prior experience monitoring halluci-
nogen sessions and a female clinically trained social worker
(M.C.) served as primary and assistant monitors, respectively,
for all study participants.
Drug sessions
The participants were instructed to consume a low-fat
breakfast before reporting to the research unit at 0800 hours,
about 1 h before drug administration. A urine sample was
taken to verify drug-free status, and the participants were
encouraged to relax and reflect before drug administration.
The 8-h drug sessions were conducted in an aesthetic living-
room-like environment designed specifically for the study.
Two monitors were present with a single participant through-
out the session. For most of the time during the session, the
participant was encouraged to lie down on the couch, use an
eye mask to block external visual distraction, and use
headphones through which a classical music program was
played. The same music program was played for all
participants in all sessions. The participants were encouraged
to focus their attention on their inner experiences throughout
the session. If a participant reported significant fear or
anxiety, the monitors provided reassurance verbally or phys-
ically (e.g., with a supportive touch to the hand or shoulder).
The sessions were videotaped and about 25% were reviewed
by the first author to verify session procedures.
Expectancy
It is widely believed that expectancy plays a large role in
the qualitative effects of hallucinogens (Metzner et al.
1965). Some expectancy effects are unavoidable because it
would be unethical not to inform both the participants and
the session monitors about the range of possible effects
with hallucinogens. In addition, it is believed by many that
ethical hallucinogen administration requires that sessions be
monitored by individuals who are familiar with such altered
states of consciousness (Masters and Houston 1966;
Roberts 2001; Stolaroff 2001). Thus, the beliefs of the
session monitors introduce another source of expectancy.
While it was not possible to completely eliminate such
expectancy effects, it was possible to significantly reduce
such effects by studying participants without personal
histories of hallucinogen use, by studying only a single
participant at a time, and by using an experimental design
and instructional sets that provided the expectation that
sessions could involve not only the administration of a wide
range of psilocybin doses but also a range of novel drugs,
some of which could produce effects that overlap with
those produced by psilocybin. Expectancy effects were also
reduced because the experimental design was further
obscured from both participants and monitors, who were
not aware of which or how many participants would have a
final unblinded psilocybin session (see “Instructions to
participants and monitors”).
Instructions to participants and monitors
The participants and monitors were informed that the
participants would have either two or three sessions and
that, in at least one session, they would receive a moderate
or high dose of psilocybin. They were informed that an
inactive placebo, a low dose of psilocybin or various doses
of 11 other drugs that could produce various effects
(dextromethorphan, nicotine, diphenhydramine, caffeine,
methylphenidate, amphetamine, codeine, alprazolam, diaz-
epam, triazolam, or secobarbital), could be administered in
Psychopharmacology
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sessions in which a moderate or high dose of psilocybin
was not administered. After data collection 2 months after
the second session, the six participants who received
methylphenidate on the first and second session were
informed that they would have a third session that would
involve administration of a moderate or high dose of
psilocybin. These six sessions were the only unblinded
sessions. To help focus the participants on their experiences
during the sessions, they were not asked to guess whether
or not they received psilocybin. However, the monitors
completed a rating form which recorded their guesses about
the contents of capsules approximately 7 h after capsule
administration but before the participant completed detailed
questionnaires describing his or her experiences. The
participants were given no information about these or any
other monitor ratings.
Measures assessed throughout the session
Ten minutes before and 30, 60, 90, 120, 180, 240, 300, and
360 min after capsule administration, monitor ratings, blood
pressure, and heart rate were obtained.
Blood pressure and heart rate Blood pressure (systolic,
diastolic, and mean arterial pressure using oscillometric method
with the blood pressure cuff placed on the arm) and heart rate
were monitored using a Non-Invasive Patient Monitor Model
507E (Criticare Systems, Waukesha, WI, USA).
Monitor rating questionnaire At the same time-points at
which the physiological measures were taken, the two
session monitors completed the Monitor Rating Question-
naire, which involved rating or scoring 20 dimensions of
the participant’s behavior or mood (Table 1). The dimen-
sions expressed as peak scores in Table 1were rated on
a five-point scale from 0 to 4. The dimensions expressed
as total duration in Table 1were rated as the estimated
number of minutes since the last rating. The data were
the mean of the two monitor ratings at each time-point.
Measures assessed 7 h after drug administration
At about 7 h after capsule administration, when the major
drug effects had subsided, the participants completed three
empirically derived (i.e., via factor analysis) questionnaires
assessing subjective drug effects and two questionnaires
assessing mystical experience, as described below. The
participants typically completed these questionnaires in
about 40 min.
Hallucinogen rating scale This 99-item questionnaire,
which was designed to show sensitivity to the hallucino-
gen N,N-dimethyltryptamine (Strassman et al. 1994; Riba
et al. 2001), consists of six subscales assessing various
aspects of hallucinogen effects (intensity, somaesthesia,
affect, perception, cognition, and volition).
APZ The APZ is a 72-item yes/no questionnaire designed
to assess altered states of consciousness induced by drug
(e.g., DMT or psilocybin) or non-drug (e.g., perceptual
deprivation, hypnosis, and sensory overload) manipulations
(Dittrich 1998). The three major scales on the APZ are the
OSE (oceanic boundlessness, a state common to classic
mystical experiences including feelings of unity and tran-
scendence of time and space), the AIA (dread of ego dis-
solution, dysphoric feelings similar to those of some “bad
trip”described by hallucinogen users), and the VUS
(visionary restructuralization, which includes items on
visual pseudo-hallucinations, illusions, and synesthesias).
The data on each scale were expressed as a proportion of
the maximum possible score.
Addiction research center inventory (ARCI) The ARCI was
developed to differentiate subjective effects among several
classes of psychoactive drugs including hallucinogens
(Haertzen 1966). The short form of the ARCI consists of
49 true/false questions and contains five major scales:
lysergic acid diethylamide (LSD, a hallucinogen-sensitive
scale that is often interpreted as providing a measure of
dysphoric changes); pentobarbital, chlorpromazine, and
alcohol group (PCAG, a sedative sensitive scale); benzedrine
group (BG); amphetamine (A) scales (amphetamine-
sensitive scales); and morphine-benzedrine group (MBG,
often interpreted as a measure of euphoria) (Martin et al.
1971;Jasinski1977). The participants were instructed to
answer the questions on the ARCI with reference to the
effects they experienced after they received the capsules that
morning.
States of consciousness questionnaire This 100-item ques-
tionnaire is rated on a six-point scale [0=none, not at all;
1=so slight, cannot decide; 2=slight; 3=moderate; 4=strong
(equivalent in degree to any previous strong experience or
expectation of this description); and 5=extreme (more than
ever before in my life and stronger than 4)]. Forty-three
items on this questionnaire comprised the current version of
the Pahnke–Richards Mystical Experience Questionnaire
(Pahnke 1969;Richards1975), which was designed to
assess mystical experiences, used as a primary outcome
measure in the Good Friday Experiment (Pahnke 1963;
Doblin 1991), and has been shown to be sensitive to other
hallucinogens (Turek et al. 1974;Richardsetal.1977). This
questionnaire is based on the classic descriptive work on
mystical experiences and the psychology of religion by Stace
(1960), and it provides scale scores for each of seven
Psychopharmacology
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domains of mystical experiences: internal unity (pure
awareness; a merging with ultimate reality); external unity
(unity of all things; all things are alive; all is one); tran-
scendence of time and space; ineffability and paradoxicality
(claim of difficulty in describing the experience in words);
sense of sacredness (awe); noetic quality (claim of intuitive
knowledge of ultimate reality); and deeply felt positive mood
(joy, peace, and love). The specific items in each of the
scales of the Pahnke–Richards Mystical Experience Ques-
tionnaire are available online as Electronic Supplementary
Material, Table 1. The data on each scale were expressed as
a proportion of the maximum possible score. Based on prior
research (Pahnke 1969), the criteria for designating a
volunteer as having had a “complete”mystical experience
were that the scores on each of the following scales had to be
at least 0.6: unity (either internal or external, whichever was
greater), transcendence of time and space, ineffability, sense
of sacredness, noetic quality, and positive mood. The
remaining 57 items in the questionnaire served as distracter
items.
Mysticism scale This 32-item questionnaire was developed
to assess primary mystical experiences (Hood et al. 2001;
Spilka et al. 2005). The Mysticism Scale has been exten-
sively studied, demonstrates cross-cultural generalizability,
and is well regarded in the field of the psychology of
religion (Hood et al. 2001; Spilka et al. 2005) but has not
previously been used to assess changes after a drug experi-
ence. A total score and three empirically derived factors are
measured: interpretation (corresponding to three mystical
dimensions described by Stace (1960): noetic quality,
deeply felt positive mood, and sacredness); introvertive
mysticism (corresponding to the Stace dimensions of
internal unity, transcendence of time and space, and
ineffability); and extrovertive mysticism (corresponding to
the dimension of the unity of all things/all things are alive).
The items were rated on a nine-point scale (−4=this
description is extremely not true of my own experience or
experiences; 0=I cannot decide; and +4=this description is
extremely true of my own experience or experiences). For
the version of the questionnaire used 7 h after drug
administration, the participants were instructed to complete
the questionnaire with reference to their experiences after
they received the capsules that morning.
Measures assessed 2 months post-session
At 7 to 8 weeks after each session and before any additional
session, the participants returned to the research facility and
completed a series of questionnaires to assess possible
persisting changes in attitudes, mood, or behavior as well as
possible changes in standardized measures of personality,
mood, and spirituality. The participants typically completed
these questionnaires in about 75 min.
At about this same time, community observer ratings of
participants’attitudes and behavior were obtained by
telephone. The outcome measures at this time-point are
described below.
Persisting Effects Questionnaire This 89-item question-
naire sought information about changes in attitudes, moods,
behavior, and spiritual experience that, on the basis of prior
research (Pahnke 1963,1969; Doblin 1991; Richards et al.
1977), would possibly be sensitive to the effects of
psilocybin 2 months after the session. Eighty-six of the
items were rated on a six-point scale (0=none, not at all;
1=so slight, cannot decide; 2=slight; 3=moderate; 4=strong;
and 5=extreme, more than ever before in your life and
stronger than 4). Sixty-six of the items were from Pahnke
(1963,1969) and 20 items were new. For purposes of
summarizing the results before data analysis, 61 of the 86
items were judged as likely to be unambiguously divided
into six categories: positive attitudes about life and/or self,
negative attitudes about life and/or self, positive mood
changes, negative mood changes, altruistic/positive social
effects, and antisocial/negative social effects. Six raters
independently sorted the 61 items into the six categories.
Three items were excluded because fewer than five of the
six raters agreed on the categories. For the remaining 58
items, at least five of the six raters agreed with the
assignment of each item to each category, suggesting the
appropriateness of the category descriptors. The category
descriptors and the number of items associated with each
category were: positive attitudes about life and/or self (17
items), negative attitudes about life and/or self (17 items),
positive mood changes (four items), negative mood changes
(four items), altruistic/positive social effects (eight items),
and antisocial/negative social effects (eight items). Two
additional categories were comprised of one item each:
positive behavior change and negative behavior change.
For scoring purposes, the eight category scores based on
a total of 60 items were expressed as the percentage of
the maximum possible score. The items in each of the
categories of the Persisting Effects Questionnaire are
available online as electronic supplementary material,
Table 2. The remaining 23 items in the questionnaire
that did not readily fit into the categories predominately
reflected aspects of spirituality and mystical experience;
these domains were characterized by other outcome
measures.
The questionnaire also included these three questions:
(1) How personally meaningful was the experience (rated
1= no more than routine, everyday experiences; 2= similar
to meaningful experiences that occur on average once or
more a week; 3=similar to meaningful experiences that
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occur on average once a month; 4=similar to meaningful
experiences that occur on average once a year; 5=similar
to meaningful experiences that occur on average once
every 5 years; 6=among the 10 most meaningful experi-
ences of my life; 7=among the 5 most meaningful
experiences of my life; and 8=the single most meaningful
experience of my life)? (2) Indicate the degree to which
the experience was spiritually significant to you (rated
1=not at all, 2=slightly, 3=moderately, 4=very much,
5=among the 5 most spiritually significant experiences
of my life, and 6=the single most spiritually significant
experience of my life). (3) Do you believe that the
experience and your contemplation of that experience
have led to change in your current sense of personal well-
being or life satisfaction (rated +3=increased very much,
+2=increased moderately, +1=increased slightly, 0=no
change, −1=decreased slightly, −2=decreased moderately,
and −3=decreased very much)?
This questionnaire was developed after the initiation of
the study and was completed by all 24 of the 30 participants
who thereafter received psilocybin and methylphenidate in
counterbalanced order in the first two sessions (12 partici-
pants in each of the two drug orders).
Mysticism Scale-Lifetime The Lifetime version of this
previously described questionnaire instructed the partici-
pants to answer questions with reference to their total life
experiences. This questionnaire was completed at screening
and at 2 months after each session.
Spiritual Transcendence Scale This 24-item questionnaire
assesses a construct that reflects an individual’s effort to
create a broad sense of personal meaning in his or her life
and has been shown to demonstrate cross-cultural general-
ity (Piedmont 1999,2005,2006; Piedmont and Leach
2002). A total score and three empirically derived factors
are scored: prayer fulfillment, universality, and connected-
ness. This questionnaire was completed at screening and at
2 months after each session.
NEO Personality Inventory (NEO PI-R) This 241-item
questionnaire, which was completed on a computer, per-
mits the assessment of five major personality factors:
neuroticism, extraversion, openness, agreeableness, and
conscientiousness (Costa and McCrae 1992). This ques-
tionnaire was completed at screening and at 2 months after
each session.
PANAS-X (Positive and Negative Affect Schedule Expanded
Form) This 60-item questionnaire permits the assessment
of two broad general factors (positive affect and negative
affect) accounting for most of the variance in self-rated
affect (Watson and Clark 1994,1997). The version of
the questionnaire used instructed the participants to
answer questions based on how they feel on the
average. This questionnaire was completed at screening
and at 2 months after each session.
Community observer ratings of changes in participants’
behavior and attitudes After acceptance into the study,
each participant designated three adults who were
expected to have continuing contact with the participant
(e.g., family members, friends, or coworkers/colleagues at
work) such that they would be likely to observe changes
in the participants’behavior and attitudes that might occur
during the study. Ratings by the designated individuals
were conducted via a structured telephone interview
approximately 1 week after the participant had been ac-
cepted into the study and 7 to 8 weeks after each of the
drug sessions. The interviewer provided no information
to the community volunteer about the participant. Fur-
thermore, most of the interviews (60%) were conducted
by a research assistant who had never met the participant
and had no knowledge about the participant’s experiences
during drug sessions. The structured interview consisted
of asking the rater to rate the volunteer’s behavior and
attitudes using a ten-point scale (from 1=not at all to
10=extremely) on 11 dimensions that were identified from
prior research (Pahnke 1963; Richards et al. 1977; Doblin
1991) as possibly sensitive to the effects of psilocybin.
The rated dimensions were: inner peace, patience, good-
natured humor/playfulness, mental flexibility, optimism,
anxiety, interpersonal perceptiveness and caring, negative
expression of anger, compassion/social concern, expression
of positive emotions (e.g., joy, love, appreciation), and
self-confidence. On the first rating occasion, which
occurred soon after acceptance into the study, the raters
were instructed to base their ratings on observations of and
conversations with the participant over the past 3 months.
On subsequent ratings, which occurred 7 to 8 weeks after
each session, the raters were told their previous ratings and
were instructed to rate the participant based on interactions
over the last several weeks. The data from each interview
with each rater were calculated as a total score, with
anxiety and anger scored negatively. The changes in
participants’behavior and attitudes after drug sessions
were expressed as a mean change score from the preceding
rating across the raters.
A failure to interview all three of the raters after one of
the drug sessions resulted in elimination of 4 of the 30
participants who received psilocybin and methylphenidate
in counterbalanced order on the first two sessions. Of the
52 rating occasions in the 26 participants, the majority
(83%) involved interviews with all three raters on each
rating occasion, with all of the remaining interviews con-
ducted with two raters.
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Data analyses
The data were statistically analyzed for the 30 participants
who received psilocybin and methylphenidate in counter-
balanced order on the first two sessions.
Physiological and monitor rating questionnaire assessed
throughout the session Two sets of analyses were con-
ducted. For the first, a two-factor analysis of variance was
used with drug (psilocybin and methylphenidate) and time
(10 min before and 0.5, 1, 1.5, 2, 3, 4, 5, and 6 h after
capsule administration) as within-subject factors. The mean
square error term for the drug × time interaction was then
used to conduct Tukey’s honestly significant differences
(HSD) post hoc tests comparing psilocybin and methylphe-
nidate at each post-drug-administration time point. For the
second set of analyses, the peak scores during the time-
course were defined as the maximum value from 0.5 to 6 h
after capsule administration, and temporally based mea-
sures (i.e., minutes sleeping and minutes speaking) were
summed across the eight post-capsule time-points. Paired t
tests were used to compare psilocybin and methylphenidate
conditions.
Measures assessed 7 h after drug administration Paired t
tests were used to compare psilocybin and methylphenidate
conditions on the three measures of subjective drug effect
(Hallucinogen Rating Scale, APZ, and Addiction Research
Center Inventory) and the two questionnaires assessing
mystical experience (States of Consciousness Questionnaire
and Mysticism Scale).
Measures assessed 2 months post-session Paired ttests
were used to compare psilocybin and methylphenidate con-
ditions for the 24 participants who completed the Persisting
Effects Questionnaire and the 26 participants for whom
complete data were obtained for the community observer
ratings of changes in participants’attitudes and behavior.
The remaining four questionnaires completed 2 months
post-session (NEO, PANAS-X, Mysticism Scale-Lifetime,
and Spiritual Transcendence Scale) provide general mea-
sures of personality, affect, and spirituality that could result
in carry-over effects from post-session 1 to post-session 2.
Accordingly, these data were analyzed using the following
planned comparisons: (1) comparison (ttest)ofdata
obtained at screening for the group of participants that
received psilocybin in session 1 (N=15) with that for the
group that received methylphenidate in session 1 (N=15),
(2) comparison (ttest) of post-session 1 data for the group
of participants that received psilocybin in session 1 (N=15)
with the group that received methylphenidate in session 1
(N=15), and (3) comparison (paired ttest) of data post-
session 1 with data post-session 2 for the group of
participants that received methylphenidate on session 1
and psilocybin on session 2 (N=15).
Results
Integrity of blinding procedures
The integrity of the blinding procedures was assessed by
having the monitors complete a questionnaire after each
session on which they guessed the capsule content and a
questionnaire at the end of the study on which they
provided their guesses about the study design. Overall,
23% of sessions were misclassified (methylphenidate
identified as psilocybin or psilocybin identified as some-
thing other than psilocybin) by one or both of the monitors.
The primary and most experienced monitor had an overall
misclassification rate of 17%. Most misclassification errors
involved rating a methylphenidate session as psilocybin. It
is interesting to note that even the primary monitor,
however, sometimes rated the psilocybin condition, which
was a high dose, as being something other than psilocybin.
On two of the three occasions on which this occurred, the
participants subsequently rated their experiences as among
the five most meaningful and spiritually significant expe-
riences of their lives. These observations suggest that the
experiences reported during psilocybin sessions were not
merely artifacts of monitor expectation or suggestion.
At the conclusion of the study, the primary monitor and
the assistant monitor completed a debriefing question-
naire in which they provided their guesses about the study
design. Both monitors believed that a range of psilocybin
doses had been administered as well as other active drugs
and placebo. Caffeine, dextromethorphan, and diphenhy-
dramine were thought likely to be the other drugs ad-
ministered, and the primary monitor specifically guessed,
based on his previous clinical experience, that methylphe-
nidate had not been administered. Thus, we conclude that
the blinding procedures overall were adequately maintained
despite the differences in the pharmacological profiles of
psilocybin and methylphenidate.
Blood pressure, heart rate, and monitor ratings throughout
the session
Both psilocybin and methylphenidate produced significant
and orderly time-related effects. For both drugs, the onset
of significant blood pressure and monitor-rated effects
occurred either at the 30- or 60-min assessment, with the
effects generally peaking from 90 to 180 min and
decreasing toward pre-drug-administration levels over the
remainder of the session (Fig. 1). Heart rate increased by
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about 10 bpm for both drugs and remained significantly
elevated over the pre-drug value throughout the session.
The volunteers were rated as showing very low sleepiness/
sedation and restlessness during sessions, with no differ-
ences between the psilocybin and methylphenidate con-
ditions (Table 1). The volunteers had a significantly greater
number of minutes talking with the monitors after methyl-
phenidate than psilocybin (72 vs 51 min, during the 6 h
after capsule ingestion), although after psilocybin they had
more physical contact (e.g., handholding) with the monitor
(24 vs 58 min) and higher peak ratings of stimulation/
arousal and spontaneous motor activity (Fig. 2; Table 1). It
is noteworthy that, during psilocybin sessions, the partic-
ipants were rated as being less responsive to questions,
further from ordinary reality, and showing greater emotion-
ality as reflected in peak ratings of tearing/crying, anxiety/
fearfulness, joy/intense happiness, and peace/harmony
(Fig. 2; Table 1).
Drug effect and mysticism measures assessed 7 h after drug
administration
Hallucinogen-sensitive questionnaires The three question-
naires developed for sensitivity to hallucinogenic drugs
showed differences between psilocybin and methylpheni-
date (Table 2). All six scales of the Hallucinogen Rating
Scale, all three scales on the APZ Questionnaire, and the
LSD scale of the ARCI were significantly higher after
psilocybin than after methylphenidate. These differences
reflect the fact that, after psilocybin, the participants
experienced alterations in mood, affect, and cognition
typical of hallucinogenic drugs. These included perceptual
changes (e.g., visual pseudo-hallucinations, illusions, and
synesthesias), labile moods (e.g., feelings of transcendence,
grief, joy, and/or anxiety), and cognitive changes (e.g.,
sense of meaning and/or ideas of reference).
A mixed pattern of results occurred on the other scales of
the ARCI. The PCAG subscale, which is sensitive to
sedative drugs, was higher after psilocybin. It is interesting
to note that the two stimulant scales showed opposite
effects. The amphetamine scale (A), which was designed to
show dose-related sensitivity to amphetamine, was signif-
icantly higher after psilocybin than after methylphenidate.
However, the benzedrine group scale (BG), which measures
amphetamine-induced increases in self-control, efficiency,
and concentration, was significantly higher after methyl-
phenidate than after psilocybin. Finally, the morphine-
benzedrine group (MBG) scale, which is considered a
Table 1 Monitor ratings of volunteer behavior and mood throughout the session
Rated description Methylphenidate Psilocybin Pvalue
Peak effects (maximum score=4)
Overall drug effect 1.10 (0.15) 3.13 (0.16) <0.001
Sleepiness/sedation 0.17 (0.07) 0.10 (0.05) N.S.
Unresponsive to questions 0.07 (0.05) 0.58 (0.20) <0.05
Anxiety or fearfulness 0.42 (0.09) 1.05 (0.17) <0.01
Stimulation/arousal 0.68 (0.12) 1.42 (0.26) <0.001
Distance from ordinary reality 1.12 (0.16) 3.12 (0.14) <0.001
Ideas of reference/paranoid thinking 0 (0) 0.17 (0.09) N.S.
Yawning 0.05 (0.03) 1.18 (0.23) <0.001
Tearing/crying 0.77 (0.13) 1.38 (0.21) <0.001
Nausea 0.12 (0.06) 0.42 (0.11) <0.01
Spontaneous motor activity 0.53 (0.17) 1.02 (0.23) <0.05
Restless/fidgety 0.18 (0.07) 0.27 (0.08) N.S.
Joy/intense happiness 0.63 (0.15) 2.03 (0.22) <0.001
Peace/harmony 0.92 (0.15) 1.90 (0.20) <0.001
Total duration in minutes (maximum score=360)
Talking with monitor 72.0 (4.8) 50.9 (2.2) <0.001
Total speech 122.2 (10.7) 106.0 (10.7) N.S.
Non-speech vocalization
a
2.2 (1.3) 16.1 (4.5) <0.01
Physical contact with monitor
b
23.7 (4.7) 57.6 (8.0) <0.001
Sleep 0.5 (0.3) 0.2 (0.2) N.S.
Strong anxiety 0.7 (0.3) 5.6 (2.7) N.S.
Data are mean scores with one SEM shown in parentheses (N=30)
N.S. not significant
a
For example, humming, sighs, laughter
b
For example, reassuring touch
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measure of drug-induced euphoria, did not differ signifi-
cantly between the drug conditions.
Measures of mystical experience At 7 h after capsule
administration, the volunteers also completed two ques-
tionnaires designed to assess primary mystical experiences
based on classic phenomenological descriptions from the
psychology of religion (Table 3). The total score and all
three empirically derived factors of the Mysticism Scale
and all seven scales on States of Consciousness Question-
naire were significantly higher after psilocybin than after
methylphenidate. Based on a priori criteria, 22 of the total
group of 36 volunteers had a “complete”mystical experi-
ence after psilocybin (ten, nine, and three participants in the
first, second, and third session, respectively) while only 4
of 36 did so after methylphenidate (two participants each in
the first and second sessions).
Measures assessed 2 months post-sessions
Persisting Effects Questionnaire As shown in Table 4,
compared to methylphenidate, psilocybin produced signif-
icantly greater elevations in ratings of positive attitudes,
mood, social effects, and behavior; the negative ratings of
these same dimensions were very low and did not differ
across the drug conditions. This questionnaire also included
ratings of the personal meaningfulness and spiritual
significance of the experience and whether the experience
changed their sense of well being or life satisfaction.
Table 4shows that these ratings were significantly higher
after psilocybin than after methylphenidate. It is remarkable
that 67% of the volunteers rated the experience with
psilocybin to be either the single most meaningful
experience of his or her life or among the top five most
meaningful experiences of his or her life (Fig. 3). In written
Table 2 Volunteer ratings on three drug-sensitive questionnaires completed 7 h after drug administration
Questionnaire Subscale description Methylphenidate Psilocybin Pvalue
Hallucinogen Rating Scale (4=maximum) Intensity 1.38 (0.14) 2.79 (0.12) <0.001
Somaesthesia 0.91 (0.10) 1.92 (0.11) <0.001
Affect 1.16 (0.10) 2.16 (0.10) <0.001
Perception 0.54 (0.11) 2.07 (0.14) <0.001
Cognition 1.03 (0.14) 2.54 (0.15) <0.001
Volition 1.39 (0.06) 1.77 (0.07) <0.001
APZ Questionnaire OSE (oceanic boundlessness) 3.30 (0.50) 8.00 (0.45) <0.001
AIA (dread of ego dissolution) 1.03 (0.21) 5.03 (0.74) <0.001
VUS (visionary restructuralization) 3.70 (0.59) 8.87 (0.47) <0.001
Addiction Research Center Inventory (ARCI) PCAG (sedative) 4.83 (0.41) 7.27 (0.58) <0.001
BG (amphetamine/self-control) 5.83 (0.38) 4.57 (0.32) <0.05
A (amphetamine) 3.80 (0.44) 5.13 (0.41) <0.05
MBG (euphoria) 6.77 (0.73) 8.60 (0.67) N.S.
LSD (hallucinogen/dysphoria) 4.33 (0.37) 7.33 (0.40) <0.001
Data are mean ratings with one SEM shown in parentheses (N=30)
N.S. not significant
0
1
2
3
0 60 120 180 240 300 36
0
Methylphenidate
Psilocybin
30 90
115
120
125
130
135
140
145
0 60 120 180 240 300 360
30 90
60
65
70
75
80
85
90
0 60 120 180 240 300 360
30 90
Minutes
Methylphenidate
Psilocybin
Methylphenidate
Psilocybin
Minutes
Minutes
Fig. 1 Within-session time-course of psilocybin and methylphenidate
effects. Blood pressure (systolic and diastolic) and monitor ratings
(mean of overall drug effect) as a function of time since capsule
ingestion (time 0=before drug administration). Data points are means
with brackets showing ±1 SEM (N=30) Filled data points indicate a
significant difference (Tukey HSD) from pre-administration of the
drug (time 0). The figure shows that, compared to methylphenidate,
psilocybin produced modestly higher elevations in blood pressure but
substantially higher monitor rating of overall drug effect
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comments, the volunteers judged the meaningfulness of the
experience to be similar, for example, to the birth of a first
child or death of a parent. Thirty-three percent of the
volunteers rated the psilocybin experience as being the
single most spiritually significant experience of his or her
life, with an additional 38% rating it to be among the top
five most spiritually significant experiences. In written com-
ments about their answers, the volunteers often described
aspects of the experience related to a sense of unity without
content (pure consciousness) and/or unity of all things.
After methylphenidate, in contrast, 8% of volunteers rated
the experience to be among the top five (but not the
single most) spiritually significant experiences. Seventy-
nine percent of the volunteers rated that the psilocybin
experience increased their current sense of personal well
being or life satisfaction “moderately”(50%) or “very
much”(29%), in contrast to 17 and 4%, respectively,
after methylphenidate. No volunteer rated either the
psilocybin or methylphenidate experience as having
decreased their sense of well being or life satisfaction.
Table 3 Volunteer ratings on two mystical experience questionnaires completed 7 h after drug administration
Questionnaire Subscale description Methylphenidate Psilocybin Pvalue
Mysticism Scale Interpretation 70.6 (4.5) 96.1 (3.3) <0.001
Introvertive 66.9 (4.4) 96.3 (2.8) <0.001
Extrovertive 37.2 (3.2) 59.7 (2.9) <0.001
Total 174.7 (11.3) 252.1 (8.5) <0.001
States of Consciousness Questionnaire
a
Internal unity 0.25 (0.05) 0.73 (0.05) <0.001
External unity 0.21 (0.05) 0.66 (0.06) <0.001
Sacredness 0.36 (0.05) 0.80 (0.04) <0.001
Intuitive knowledge 0.30 (0.05) 0.72 (0.05) <0.001
Transcendence of time and space 0.27 (0.05) 0.76 (0.04) <0.001
Deeply felt positive mood 0.38 (0.04) 0.77 (0.05) <0.001
Ineffability 0.29 (0.05) 0.81 (0.05) <0.001
Data are mean scores with one SEM shown in parentheses (N=30)
N.S. not significant
a
For States of Consciousness Questionnaire, data are expressed as a proportion of the maximum possible score
*
Talking with Monitor
MINUTES (TOTAL)
Methp Psilocybin
0
1
2
3
*
Stimulation/Arousal
PEAK SCORE
40
50
60
70
80
Methp Psilocybin
PEAK SCORE
*
Anxiety/Fearfulness
0
1
2
3
*
Joy/Intense Happiness
0
1
2
3
*
Peace/Harmony
0
1
2
3
PEAK SCORE
PEAK SCORE
Tearing/Crying
*
Methp Psilocybin
PEAK SCORE
0
1
2
3
Fig. 2 Monitor ratings during sessions. Bars are mean ratings with 1 SEM shown in brackets (N=30). Asterisks indicate a significant difference
between the methylphenidate (Methp) and psilocybin conditions. Maximum possible rating=4
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Personality and affect None of the factors on the two
widely used questionnaires assessing five factors of
personality (NEO and PI-R) and measures of general
positive and negative affect (PANAS-X) was differentially
affected by psilocybin. At screening and at 2 months after
session 1, there were no significant differences between the
group that received psilocybin on the first session (N=15)
and the group that received methylphenidate on the first
session (N=15). Furthermore, within the latter group, there
were no significant changes from post-session 1 to post-
session 2.
Lifetime assessment of mystical experience and spirituali-
ty Two additional questionnaires completed 2 months after
each session provided lifetime measures of mystical
experiences (Mysticism Scale) and spirituality (Spiritual
Transcendence Scale). As with the measures of personality
and affect, there were no significant differences at screening
between the group that received psilocybin on the first
session (N=15) and the group that received methylpheni-
date on the first session (N=15). As shown in Fig. 4,at
2 months after the first session, lifetime mystical experience
and spiritual transcendence scores were significantly higher
in the group that received psilocybin on the first session
than the group that received methylphenidate on the first
session. At 2 months after the second session, the scores in
the group that received psilocybin on the second session
increased significantly on both measures. As expected,
because these scores reflect lifetime measures, these scores
did not decrease after the second session in the group that
received psilocybin on the first session.
Community observer ratings of changes in participants’
and behavior and attitudes Table 4shows that, compared
to methylphenidate, psilocybin sessions were associated
with small but significant positive changes in the par-
ticipants’behavior and attitudes.
Fear, anxiety/dysphoria, and ideas of reference/paranoia
According to monitor ratings, post-session ratings and
written comments by the monitors and the participants,
and post-session interviews with the participants, many
participants reported mild or moderate anticipatory anxiety
at the beginning of sessions. In post-session ratings, 11 of
the 36 total volunteers after psilocybin and none after
methylphenidate rated on the States of Consciousness
Questionnaire their “experience of fear”sometime during
the session to be “strong”or “extreme.”Four volunteers (all
of whom had high post-session fear ratings) reported that
their entire session was dominated by anxiety or unpleasant
psychological struggle (i.e., dysphoria). Four others (again,
all of whom had high post-session fear ratings) reported
that a significant portion of their session was characterized
by anxiety/dysphoria. Although the onset of episodes of
notable anxiety/dysphoria was most likely to occur shortly
after onset of drug effect, there were occasions on which
onset occurred later in the session when drug effects were
Table 4 Volunteer ratings and community observer ratings completed 2 months after sessions
Outcome measures Description Methylphenidate Psilocybin Pvalue
Persisting Effects Questionnaire
(volunteer ratings)
a
Positive attitudes about life and/or self and/or self 22.8 (4.5) 55.0 (5.0) <0.001
Negative attitudes about life and/or self 0.3 (0.1) 0.5 (0.3) N.S.
Positive mood changes 16.0 (3.5) 39.2 (5.3) <0.001
Negative mood changes 0.6 (0.5) 1.5 (0.7) N.S.
Altruistic/positive social effects 17.3 (4.4) 46.6 (5.5) <0.001
Antisocial/negative social effects 0.3 (0.2) 0.7 (0.5) N.S.
Positive behavior changes 29.2 (6.5) 60.0 (4.8) <0.001
Negative behavior changes 1.7 (1.2) 0 (0) N.S.
How personally meaningful was the experience? 3.42 (0.35) 6.54 (0.22) <0.001
How spiritually significant was the experience? 2.63 (0.22) 4.79 (0.26) <0.001
Did the experience change your sense of well
being or life satisfaction?
+0.79 (0.18) +2.04 (0.17) <0.001
Community observer ratings of changes in
participants’behavior and attitudes
b
Positive change score −0.03 (0.68) 2.42 (0.70) <0.01
Data are mean ratings with one SEM shown in parentheses
N.S. Not significant
a
For Persisting Effects Questionnaire, data on attitude, mood, social, and behavior changes are expressed as percentage of maximum possible
score, and data for the last three questions are raw scores; for volunteer ratings, N=24 (cf., “Materials and methods”)
b
For ratings by community observers, data are mean positive change scores; for observer ratings, N=26 (cf., “Materials and methods”)
Psychopharmacology
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subsiding. Anxiety/dysphoria occurred when psilocybin
was administered on the first (two participants), second
(four participants), and third (two participants) sessions,
suggesting that longer preparation time and being unblind-
ed to psilocybin administration were not protective. Six of
the eight volunteers with a notable anxiety/dysphoria
response had mild, transient ideas of reference/paranoid
thinking sometime during the 6 h after psilocybin admin-
istration. These effects were readily managed with reassur-
ance and did not persist beyond the session. Two of the
eight volunteers compared the experience to being in a war
and three indicated that they would never wish to repeat an
experience like that again. Despite these psychological
struggles, most of these participants rated the overall
experience as having personal meaning and spiritual
significance and no volunteer rated the experience as
having decreased their sense of well being or life
satisfaction.
Discussion
The present double-blind study shows that psilocybin,
when administered under comfortable, structured, interper-
sonally supported conditions to volunteers who reported
regular participation in religious or spiritual activities,
occasioned experiences which had marked similarities to
classic mystical experiences and which were rated by
volunteers as having substantial personal meaning and
spiritual significance. Furthermore, the volunteers attributed
to the experience sustained positive changes in attitudes and
behavior that were consistent with changes rated by friends
and family.
The present study advances the empirical analysis of
mystical experience. From a scientific perspective, most of
what is known about mystical or religious experience is
based on descriptive characterization of spontaneously
occurring experience (Stace 1960; Spilka et al. 2005).
Psilocybin
Methylphenidate
How Personally Meaningful Was the Experience?
(Rated 2 months after session, N=24)
0 102030405060
Once a Week
Once a Month
Once a Year
Once Every 5 Years
Among Top Ten
Among Top Five
Single Most (Lifetime)
Percenta
g
e of Volunteers
Everyday Experience
Fig. 3 Percentage of volunteers
who endorsed each of eight
possible answers to the question
“how personally meaningful
was the experience?”on a
questionnaire completed
2 months after the session
(N=24)
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Rigorous attempts to prospectively experimentally manip-
ulate such experiences have generally been associated with
only modest effects (e.g., Hood et al. 1990; Spilka et al.
2005). Although there are anecdotal reports from the
clinical research in the 1960s of hallucinogens occasioning
religious experiences, even when administered in a secular
setting (Smith 1964; Masters and Houston 1966; Dobkin de
Rios and Janiger 2003), a systematic study of such effects
has been almost nonexistent. The most relevant study was
one in which theological seminary students received either
30 mg psilocybin (ten participants) or 200 mg nicotinic acid
(ten participants) in a group setting during a religious
service (the Good Friday Experiment, Pahnke 1963;1967;
Doblin 1991). The participants who received psilocybin
showed significant elevations on the Pahnke Mystical
Experience Questionnaire and reported positive changes in
attitudes and behavior at 6 months and at 25-year follow-
up. Those results are consistent with the present study,
which also demonstrated sustained increases on two closely
related outcome measures (Pahnke–Richards Mystical
190
200
210
220
230
240
250
260
270
MYSTICISM SCALE
*
*
2 Months after 1st Session 2 Months after 2nd Session
Methp 1st
Psil 2nd
Psil 1st
Methp 2nd
90
95
100
105
110
2 Months after 1st Session
SPIRITUAL TRANSCENDENCE SCALE
2 Months after 2nd Session
*
*
Methp 1st
Psil 2nd
Psil 1st
Methp 2nd
Methp 1st
Psil 2nd
Psil 1st
Methp 2nd
Methp 1st
Psil 2nd
Psil 1st
Methp 2nd
Fig. 4 Lifetime mystical expe-
rience (Mysticism Scale) and
spirituality (Spiritual Transcen-
dence Scale) scores 2 months
after the first session (left two
columns) and 2 months after the
second session (right two col-
umns) in two groups of partic-
ipants. One group (N=15)
received methylphenidate on the
first session and psilocybin on
the second session (Methp 1st,
Psil 2nd) and the other group
(N=15) received the reverse or-
der (Psil 1st,Methp 2nd). Bars
are means with brackets show-
ing one SEM. Asterisks indicate
a significant difference
between the conditions
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Experience Questionnaire and Persisting Effects Question-
naire). Significant limitations of the Pahnke study were that
the participants were explicitly told that some would
receive psilocybin and some would be controls, and that it
was conducted in a group setting. These features resulted in
the double-blind being quickly broken during the session,
which presumably contributed to the assessed differences
between the groups (Doblin 1991; Wulff 1991; Smith
2000). The present study represents an important extension of
the Pahnke study using better blinding and comparison
control procedures, assessment of effects in individual
participants unconfounded by group interactions, empirically
validated measures of mystical experience (the Mysticism
Scale and the Spiritual Transcendence Scale), and assessment
of effects by community observers. The credibility of the
blinding procedure is reflected in the facts that the debriefing
interviews with the monitors at the end of the study indicated
that they remained unaware of the study design and that some
volunteers rated their experience during the methylphenidate
session as being among the most personally meaningful
experiences of their lives (Fig. 3).
The proportion of volunteers who fulfilled Pahnke’s criteria
for having a “complete”mystical experience (61%, 22 of 36)
is somewhat higher than the 30–40% reported by Pahnke in
the Good Friday Experiment (cf. Pahnke 1967, p 67). It seems
likely that the greater preparation time (at least 8 versus 3 h in
the Pahnke study) and the differences in context (individual
sessions with an eye mask and music in an aesthetic room
verses the Pahnke study conducted in a group setting with 30
individuals, some of whom were acting bizarrely) likely
contributed to this difference. The present study provides no
evidence that preparation beyond that given before the first
session produced an increase in the incidence of a mystical
experience (i.e., on the first, second, and third session,
respectively, 67, 60, and 50% of participants who received
psilocybin met the criteria for a complete mystical experi-
ence) or a decrease in the incidence of anxiety/dysphoria.
The extent to which the study population limits the
generalizability of the results is unknown. The participants in
this study were hallucinogen-naïve, well educated, psycho-
logically stable, and middle-aged adults, who reported
regular participation in religious or spiritual activities. In
particular, it seems plausible that the religious or spiritual
interest of the participants may have increased the likelihood
that the psilocybin experience would be interpreted as
having substantial spiritual significance and personal mean-
ing. It is also unknown how the hallucinogen-naïve status of
the participants affected either the intensity or qualitative
interpretation of the experience. Recruiting volunteers
without histories of use avoided the problem of participant
selection bias in which individuals who had previously had
positive experiences with hallucinogens would have been
most likely to participate. However, it is also possible that
the novelty of the experience in hallucinogen-naïve individ-
uals enhanced both the intensity and the personal and
spiritual significance of the experience.
An important finding of the present study is that, with
careful volunteer screening and preparation and when
sessions are conducted in a comfortable, well-supervised
setting, a high dose of 30 mg/70 kg psilocybin can be
administered safely. It is also noteworthy that, despite
meetings and prior sessions with monitors ranging from
8 h (when psilocybin was administered on the first session)
up to 24 h (when psilocybin was administered on the third
session) of contact time, 22% (8 of 36) of the volunteers
experienced a period of notable anxiety/dysphoria during the
session, sometimes including transient ideas of reference/
paranoia. No volunteer required pharmacological interven-
tion and the psychological effects were readily managed with
reassurance. The primary monitor remained accessible via
beeper/phone to each volunteer for 24 h after each session,
but no volunteer called before the scheduled follow-up
meeting on the next day. The 1-year follow-up is ongoing
but has been completed by most volunteers (30 of 36). In
that follow-up, an open-ended clinical interview reflecting
on the study experiences and current life situation provides a
clinical context conducive to the spontaneous reporting of
study-associated adverse events. To date, there have been no
reports of persisting perceptional phenomena sometimes
attributed to hallucinogen use or of recreational abuse of
hallucinogens, and all participants appear to continue to be
high-functioning, productive members of society.
The results of the present study have implications for
understanding the abuse of hallucinogens. Although psilo-
cybin is regulated by the federal government under the
most restrictive category (Schedule I) of the Controlled
Substances Act, the National Institute on Drug Abuse
(2001,2005) does not consider psilocybin and the other
classical hallucinogens to be drugs of “addiction”because
they do not produce compulsive drug-seeking behavior as
do classic addicting drugs such as cocaine, amphetamine,
heroin, and alcohol. This conclusion is consistent with
observations that psilocybin and other classic hallucinogens
do not maintain reliable drug self-administration in animal
laboratory models of drug abuse (Griffiths et al. 1980;
Fantegrossi et al. 2004) and that most recreational users of
classical hallucinogens decrease or stop their use over time
(National Institute on Drug Abuse 2001). In the present
study, psilocybin did not produce a classic euphorigenic
profile of effects: measures of anxiety and dysphoria
(monitor ratings of anxiety: AIA scale on the APZ
Questionnaire, LSD scale on the ARCI) were significantly
greater after psilocybin than after methylphenidate. How-
ever, the present study also shows that, in some people
under some conditions, psilocybin can occasion experien-
ces that are rated as highly valued. This seems a likely
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mechanism underlying the long-term historical use of
psilocybin and other hallucinogens such as DMT within
some cultures for divinatory or religious purposes.
While there is no indication that carefully monitored
clinical exposure of psilocybin to hallucinogen-naïve
volunteers results in subsequent abuse (present study;
Gouzoulis-Mayfrank, personal communication; Yensen
and Dryer, (1992)
1
;Leuner1981), the epidemic of
hallucinogen abuse in the 1960s raises an important
cautionary note. Abuse of hallucinogens can be exacerbated
under conditions in which hallucinogens are readily
available illicitly and the potential harms to both the
individual and society are misrepresented or understated.
It is important that the risks of hallucinogen use not be
underestimated. Even in the present study in which the
conditions of volunteer preparation and psilocybin admin-
istration were carefully designed to minimize adverse
effects, with a high dose of psilocybin 31% of the group
of carefully screened volunteers experienced significant
fear and 17% had transient ideas of reference/paranoia.
Under unmonitored conditions, it is not difficult to imagine
such effects escalating to panic and dangerous behavior.
Also, the role of hallucinogens in precipitating or exacer-
bating enduring psychiatric conditions and long-lasting
visual perceptual disturbances should remain a topic of
research (Abraham et al. 1996; Halpern and Pope 1999).
In conclusion, the present study showed that, when
administered to volunteers under supportive conditions,
psilocybin occasioned experiences similar to spontaneous-
ly occurring mystical experiences and which were
evaluated by volunteers as having substantial and sus-
tained personal meaning and spiritual significance. The
ability to prospectively occasion mystical experiences
should permit rigorous scientific investigations about their
causes and consequences, providing insights into under-
lying pharmacological and brain mechanisms, nonmedical
use and abuse of psilocybin and similar compounds, as
well as the short-term and persisting effects of such
experiences.
Acknowledgements This research was supported by NIDA grant
R01 DA03889 and a grant from the Council on Spiritual Practices.
We thank Dave Nichols, Ph.D., for synthesizing the psilocybin, Mary
Cosimano, M.A., for her role as assistant monitor, Brian Richards,
Psy.D. and Kori Kindbom, M.A., for psychiatric screening, Heather
Cronin for data management, Paul Nuzzo, M.A., for statistical
analysis, Matthew W. Johnson, Ph.D., for discussions about the data,
and Dr. George Bigelow, Dr. Eric Strain, Dr. Maxine Stitizer, and Dr.
Larry Carter for comments on the manuscript. The study was
conducted in compliance with US laws.
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Electronic Supplementary Material (ESM) – two items for inclusion with the online version
ESM Table 1. States of Consciousness Questionnaire and Pahnke-Richards Mystical Experience
Questionnaire
ESM Table 2. Items in the Persisting Effects Questionnaire used to assess eight categories of possible
change in attitudes, mood, social effects, and behavior.
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Electronic Supplementary Material
EMS Table 1. States of Consciousness Questionnaire and Pahnke-Richards Mystical Experience Questionnaire
Instructions:
Looking back on the extended session you have just experienced, please rate the degree to which at any time during that
session, you experienced the following phenomena. In making each of your ratings, use the following scale:
0 – none; not at all.
1 – so slight cannot decide
2 – slight
3 – moderate
4 - strong (equivalent in degree to any previous strong experience or expectation of this description)
5 – extreme (more than ever before in my life and stronger than 4)
Items and Scoring: There are 100 items in the States of Consciousness Questionnaire. Forty-three items on this
questionnaire comprise the Pahnke-Richards Mystical Experience Questionnaire which provides scale scores for each of
seven domains of mystical experiences: Internal Unity (6 items); External Unity (6 items); Transcendence of Time and Space
(8 items); Ineffability and Paradoxicality (5 items); Sense of Sacredness (7 items); Noetic Quality (4 items); and Deeply-Felt
Positive Mood (7 items). Data on each scale are expressed as a proportion of the maximum possible score. The remaining
57 items in the questionnaire served as distracter items and were not scored. Numerals associated with each item indicate
the numerical sequence of the items.
I. Internal Unity
26. Loss of your usual identity.
35. Freedom from the limitations of your personal self and feeling a unity or bond with what was felt to be greater than
your personal self.
41. Experience of pure Being and pure awareness (beyond the world of sense impressions).
54. Experience of oneness in relation to an “inner world” within.
77. Experience of the fusion of your personal self into a larger whole.
83. Experience of unity with ultimate reality.
II. External Unity
14. Experience of oneness or unity with objects and/or persons perceived in your surroundings
27. With eyes open, seeing something in your surroundings more and more intensely and then feeling as though you
and it become one.
47. Experience of the insight that “all is One”.
51. Loss of feelings of difference between yourself and objects or persons in your surroundings.
62. Intuitive insight into the inner nature of objects and/or persons in your surroundings.
74. Awareness of the life or living presence in all things.
III. Transcendence of Time and Space
2. Loss of your usual sense of time.
12. Feeling that you experienced eternity or infinity.
15. Loss of your usual sense of space.
29. Loss of usual awareness of where you were.
34. Sense of being “outside of” time, beyond past and future.
42. Feeling that you have been “outside of” history in a realm where time does not exist.
48. Being in a realm with no space boundaries.
65. Experience of timelessness.
IV. Ineffability and Paradoxicality
6. Sense that the experience cannot be described adequately in words.
19. Experience of a paradoxical awareness that two apparently opposite principles or situations are both true.
23. Feeling that you could not do justice to your experience by describing it in words.
59. Sense that in order to describe parts of your experience you would have to use statements that appear to be
illogical, involving contradictions and paradoxes.
86. Feeling that it would be difficult to communicate your own experience to others who have not had similar
experiences.
V. Sense of Sacredness
5. Experience of amazement.
8. Sense of the limitations and smallness of your everyday personality in contrast to the Infinite.
31. Sense of profound humility before the majesty of what was felt to be sacred or holy.
36. Sense of being at a spiritual height.
55. Sense of reverence.
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73. Feeling that you experienced something profoundly sacred and holy.
80. Sense of awe or awesomeness.
VI. Noetic Quality
3. Feeling that the consciousness experienced during part of the session was more real than your normal awareness
of everyday reality.
9. Gain of insightful knowledge experienced at an intuitive level.
22. Certainty of encounter with ultimate reality (in the sense of being able to “know” and “see” what is really real ) at
some time during your session.
69. You are convinced now, as you look back on your experience, that in it you encountered ultimate reality (i.e. that
you “knew” and “saw” what was really real).
VII. Deeply-Felt Positive Mood
10. Experience of overflowing energy.
18. Feelings of tenderness and gentleness.
30. Feelings of peace and tranquillity.
43. Experience of ecstasy.
50. Feelings of exaltation.
60. Feelings of universal or infinite love.
87. Feelings of joy.
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Electronic Supplementary Material
ESM Table 2. Items in the Persisting Effects Questionnaire used to assess eight categories of possible change in attitudes,
mood, social effects, and behavior: I. positive attitudes about life and/or self (17 items); II. negative attitudes about life and/or
self (17 items); III. positive mood changes (4 items); IV. negative mood changes (4 items); V. altruistic/positive social effects (8
items); VI. antisocial/negative social effects (8 items); VII. positive behavior changes (1 item); and VIII. negative behavior
changes (1 item). Numerals associated with each item indicate the numerical sequence of the items.
I. Positive Attitudes about Life or Self
1. The experience has changed your philosophy of life positively.
6. You have more personal integration.
16. Your appreciation for life has increased.
18. You have a greater sense of inner authority in your life.
21. Your life has a heightened dynamic quality.
22. Your life has more meaning.
36. You are a more creative person.
37. You have more enthusiasm for life in general.
39. Your sense of values (i.e., what is important to you in life) has changed positively.
44. Your life has more richness.
59. You are a more authentic person.
64. Your experience has been valuable for your life.
68. You have more good-natured humor/playfulness/lightness of being.
72. You have more patience/ability to tolerate frustration.
73. You have more mental flexibility/open-mindedness.
75. You have more optimism.
85. Your self-confidence/self-assurance has increased.
II. Negative Attitudes about Life or Self
2. The experience has changed your philosophy of life negatively.
5. You have less personal integration.
17. Your appreciation for life has decreased.
19. You have a lesser sense of inner authority in your life.
20. Your life has a diminished dynamic quality.
23. Your life has less meaning.
35. You are a less creative person.
38. You have less enthusiasm for life in general.
40. Your sense of values (i.e., what is important to you in life) has changed negatively.
43. Your life has less richness.
60. You are a less authentic person.
65. Your experience has been a hindrance for your life.
67. You have less good-natured humor/playfulness/lightness of being.
71. You have less patience/ability to tolerate frustration.
74. You have less mental flexibility/open-mindedness.
76. You have less optimism.
86. Your self-confidence/self-assurance has decreased.
III. Positive Mood Changes
15. Feelings of depression have decreased.
30. Feelings of anxiety have decreased.
69. You have more inner peace (i.e. centeredness, serenity, calmness).
84. Your expression of positive emotions (e.g. love, joy, appreciation) has increased.
IV. Negative Mood Changes
14. Feelings of depression have increased.
29. Feelings of anxiety have increased.
70. You have less inner peace (i.e. centeredness, serenity, calmness).
83. Your expression of positive emotions (e.g. love, joy, appreciation) has decreased.
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EMS Table 1 (continued)
V. Altruistic/Positive Social Effects
3. You have become more sensitive to the needs of others.
10. You now feel a greater need for service for others.
24. You are more tolerant toward others.
33. You have a more positive relationship with others.
51. You now feel more love toward others.
78. You have greater interpersonal perceptiveness (i.e., sensitivity).
80. Your negative expression of anger (e.g. ridicule, outward expression of irritability
toward others) has decreased.
81. Your social concern/compassion has increased.
VI. Antisocial/Negative Social Effects
4. You have become less sensitive to the needs of others.
11. You now feel a lesser need for service for others.
25. You are less tolerant toward others.
34. You have a more negative relationship with others.
50. You now feel more hatred toward others.
77. You have reduced interpersonal perceptiveness (i.e. sensitivity).
79. Your negative expression of anger (e.g. ridicule, outward expression of irritability
toward others) has increased.
82. Your social concern/compassion has decreased.
VII. Positive Behavioral Changes
9. Your behavior has changed in ways you would consider positive since the experience.
VIII. Negative Behavioral Changes
8. Your behavior has changed in ways you would consider negative since the experience
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