Content uploaded by Leor Roseman
Author content
All content in this area was uploaded by Leor Roseman on Jul 11, 2019
Content may be subject to copyright.
https://doi.org/10.1177/0269881119855974
Journal of Psychopharmacology
1 –12
© The Author(s) 2019
Article reuse guidelines:
sagepub.com/journals-permissions
DOI: 10.1177/0269881119855974
journals.sagepub.com/home/jop
Introduction
Psychedelic therapy is a re-emerging paradigm within mental
health research (Schenberg, 2018). It is hypothesised that both
biological and psychological processes play a role in this treat-
ment, potentially working synergistically to determine therapeu-
tic outcomes (Carhart-Harris, 2018; Carhart-Harris et al., 2017b).
From a purely psychological perspective, most studies to-date
have focused on the involvement of the mystical-type experience
in determining long-term responses to psychedelics (Bogenschutz
et al., 2015; Dakwar et al., 2014; Erritzoe et al., 2018; Garcia-
Romeu et al., 2014; Griffiths et al., 2016; Johnson et al., 2016;
Klavetter and Mogar, 1967; Kurland et al., 1972; MacLean et al.,
2011; O’Reilly and Funk, 1964; Pahnke et al., 1970; Richards
et al., 1977; Roseman et al., 2017; Ross et al., 2016) and see
Stace (1960) for some classical texts relevant to the mystical
experience. Influential measures used to operationally define the
mystical experience include factors within the altered states of
consciousness questionnaire (Dittrich, 1998; Studerus et al.,
2010) and the more recently validated Mystical Experience
Questionnaire (MEQ) (MacLean et al., 2012; Pahnke and
Richards, 1966). It is now a well-replicated finding that the qual-
ity of the acute psychedelic experience is a key determinant of
longer-term responses to psychedelics – and the mystical type
experience seems to be relevant and important in this regard.
However, this does not imply that the construct is well-defined,
or that it is the sole, or indeed, primary determinant of long-term
psychological outcomes.
Another key component of the acute psychedelic experience
that has been found to be influential in determining long-term
responses is the challenging experience (CE) (Barrett et al., 2016).
Perhaps the best available tool for measuring CEs is the recently
validated Challenging Experience Questionnaire (CEQ). This
scale was developed with the intention of quantifying challenging
emotions such as grief, fear, paranoia, etc. (Barrett et al., 2016).
Recent studies have suggested that higher scores of the CEQ and
other measures of CE can predict worse longer-term mental health
Emotional breakthrough and psychedelics:
Validation of the Emotional Breakthrough
Inventory
Leor Roseman1, Eline Haijen1, Kelvin Idialu-Ikato1,
Mendel Kaelen1,2, Rosalind Watts1 and Robin Carhart-Harris1
Abstract
Background: Psychedelic therapy is gaining recognition and the nature of the psychedelic experience itself has been found to mediate subsequent
long-term psychological changes. Much emphasis has been placed on the occurrence of mystical-type experiences in determining long-term responses
to psychedelics yet here we demonstrate the importance of another component, namely: emotional breakthrough.
Methods: Three hundred and seventy-nine participants completed online surveys before and after a planned psychedelic experience. Items pertaining
to emotional breakthrough were completed one day after the psychedelic experience, as were items comprising the already validated Mystical
Experience Questionnaire and the Challenging Experience Questionnaire. Emotional breakthrough, Mystical Experience Questionnaire and Challenging
Experience Questionnaire scores were used to predict changes in well-being (Warwick-Edinburgh Mental Wellbeing Scale) in a subsample of 75
participants with low well-being baseline scores (⩽45).
Results: Factor analyses revealed six emotional breakthrough items with high internal consistency (Cronbach’s alpha=0.932) and supported our
prior hypothesis that emotional breakthrough is a distinct component of the psychedelic experience. Emotional breakthrough scores behaved dose-
dependently, and were higher if the psychedelic was taken with therapeutic planning and intent. Emotional breakthrough, Mystical Experience
Questionnaire and Challenging Experience Questionnaire scores combined, significantly predicted subsequent changes in well-being (r=0.45, p=0.0005,
n=75), with each scale contributing significant predictive value. Emotional breakthrough and Mystical Experience Questionnaire scores predicted
increases in well-being and Challenging Experience Questionnaire scores predicted less increases.
Conclusions: Here we validate a six-item ‘Emotional Breakthrough Inventory’. Emotional breakthrough is an important and distinct component of the
acute psychedelic experience that appears to be a key mediator of subsequent longer-term psychological changes. Implications for psychedelic therapy
are discussed.
Keywords
Psychedelics, catharsis, emotion, therapy
1Department of Medicine, Imperial College London, London, UK
2Wavepaths Ltd, London, UK
Corresponding author:
Leor Roseman, Department of Medicine, Imperial College London,
Hammersmith Campus, Du Cane Road, London, W2 5PB, UK.
Email: leor.roseman13@imperial.ac.uk
855974JOP0010.1177/0269881119855974Journal of PsychopharmacologyRoseman et al.
research-article2019
Original Article
2 Journal of Psychopharmacology 00(0)
outcomes, thus suggesting that CE might be counter-therapeutic
and perhaps even iatrogenic (Barrett et al., 2016; Carbonaro et al.,
2016; Haijen et al., 2018; Roseman et al., 2017), although there
are some contradictory findings in this regard, suggesting a more
complex relationship (Barrett et al., 2016; Carbonaro et al., 2016).
A major limitation of the CEQ however, is that it measures differ-
ent challenging emotions and/or memories without addressing
their potential resolution, and consequently is not able to quantify
the potential clinical value of accepting and/or overcoming the
relevant challenges (Watts et al., 2017).
Here, we endeavoured to examine a third potential mediator
of longer-term responses to psychedelics, based on the assump-
tion that the MEQ and CEQ do not fully or clearly capture the
phenomenon of overcoming challenging emotions/memories and
thereby experiencing emotional release or breakthrough. The
phenomenon of emotional breakthrough (EB) overlaps to some
extent with the psychoanalytic notion of catharsis (Breuer and
Freud, 1895; Jackson, 1994). We call the questionnaire we have
constructed and validated here, the Emotional Breakthrough
Inventory (EBI). Unlike the CEQ, which appears to be a ‘nega-
tive’ predictor of clinical outcomes (i.e. higher CEQ scores pre-
dict worse mental health outcomes), we theorised that EBI would
serve as a positive predictor of mental health, i.e. higher scores
would predict better mental health outcomes such as increases in
well-being. The development and use of the EBI in intended to
supplement the use of the CEQ and MEQ and motivate further
critique of all of three measures and the real-world phenomena
they are intended to capture.
The most often-used approach in modern psychedelic therapy
trials has its basis in work advanced by the collaboratory effort of
Al Hubbard, Humphry Osmond and Abram Hoffer in the 1950s
(Dyck, 2006; MacLean et al., 1961; Osmond, 1957). The focus of
the so-called ‘psychedelic’ model is to use relatively high doses
of a given psychedelic to promote the attainment of a powerful
self-transcendent state that may be positively transformative in
effect. The other major alternative therapeutic model, is the so-
called ‘psycholytic’ (mind-loosening) model. This approach used
lower doses of a psychedelic in concert with psychoanalytically
oriented psychotherapy. Despite differences, mainly related to
dose and number of sessions (i.e. higher doses but fewer sessions
in psychedelic therapy), both of the psychedelic and psycholytic
models emphasised the importance of emotional release.
One early account of Lysergic Acid Diethylamide’s (LSD)
therapeutic action stated that drug works to break emotional or
memory blocks and ‘in almost every case… terminates in psy-
cho-catharsis, [causing] the patient to experience an exhilarating
feeling of liberation’ (Frederking, 1955: 263). Other psychedelic
therapists, with allegiances to varying psychoanalytic schools,
shared this appreciation of the importance of EB (Bonny and
Pahnke, 1972; Cohen, 1959; Crocket et al., 1963; Eisner and
Cohen, 1958; Fisher, 2015; Grof et al., 1980; Jensen, 1963;
Katzenelbogen and Fang, 1953; Leuner, 1961; Martin, 1957;
Richards, 2015; Sandison, 1955), and patients often make special
reference to it in post-treatment reports (Belser et al., 2017;
Gasser et al., 2014; Watts et al., 2017). EBs are often accompa-
nied by and related to personal and interpersonal insights, and are
therefore not necessarily transpersonal in the same way – or to
the same extent – that mystical-type or peak experiences appear
to be (Belser et al., 2017; Gasser et al., 2014; Grof, 1975;
Loizaga-Velder, 2013; Richards, 2015; Watts et al., 2017).
The present study sought to develop and validate a brief
EBI that is focused and concise in nature. Specifically, we
assessed its internal, convergent, divergent and predictive
validity. This was done using an online prospective survey in
which participants answered questionnaires before and after
drug intake in their own environment rather than e.g. in a labo-
ratory. The sample was self-selecting and comprised mostly of
healthy individuals, thus, to combat the issue of floor effects, a
well-validated measure of psychological well-being was used
as the primary dependent variable and index of post-psyche-
delic change in psychological/emotional health. We hypothe-
sised that:
○H1: Scores on the EBI will increase in a dose-dependent
manner.
○H2: A therapeutic context (therapeutic intention before
drug intake and a therapeutic setting) will be associated
with higher EBI scores.
○H3: EBI scores will significantly discriminate from MEQ
and CEQ scores.
○H4: EBI will predict changes in well-being.
○H5: A model incorporating EBI, MEQ and CEQ will pre-
dict changes in well-being, with EBI performing at least
as well as the MEQ and CEQ.
Method
The study was approved by Imperial College Research Ethics
Committee and the Joint Research Compliance Office at Imperial
College London and carried out in accordance with principles of
good clinical practice. Written informed consent was obtained
from all subjects. The original survey has now closed but revised
and still active versions of related surveys can be found here at
www.psychedelicsurvey.com.
Software
Statistical analyses were conducted on SPSS 25 and Matlab
2017.
Design
The data presented in this article was collected as part of a larger
prospective study (Haijen et al., 2018). Only elements of the
design and data that are relevant to this article are presented
here. Data was collected from psychedelic ‘users’ in a non-con-
trolled, naturalistic and observational manner. Data was col-
lected on-line, through the website and software platform
psychedelicsurvey.com. The study was advertised via social
media platforms. The baseline time-point was one week before a
planned psychedelic experience and the key end-point was two
weeks post the relevant experience. The following data were
collected at baseline: demographics, intentions for the experi-
ence (see below), and the Warwick-Edinburgh Mental Wellbeing
Scale (WEMWBS) which served as the primary and sole
dependent variable. Retrospective reports of the acute experi-
ence were answered one day after the relevant psychedelic expe-
rience. These included: EBI, MEQ, CEQ, dose and whether the
Roseman et al. 3
experience took place in a therapeutic setting (see below). Long-
term outcomes were collected two weeks after the experience.
The WEMWBS serving as the sole dependent variable for the
present analysis. Data of 379 participants have been used for
most of the analysis in this article, however, a subset of 75 par-
ticipants with low well-being baseline scores (WEMWBS⩽45)
have been used for prediction of changes in well-being (more
information below).
Item selection and face validity
The items of EBI were devised based on interview content from
our previous psilocybin for treatment-resistant depression trial
(Watts et al., 2017) and knowledge of the extensive literature and
personal observations on the phenomenology of the psychedelic
experience and its therapeutic application (Belser et al., 2017;
Bonny and Pahnke, 1972; Cohen, 1959; Crocket et al., 1963;
Eisner and Cohen, 1958; Fisher, 2015; Frederking, 1955; Gasser
et al., 2014; Grof et al., 1980; Jensen, 1963; Katzenelbogen and
Fang, 1953; Leuner, 1961; Martin, 1957; Richards, 2015;
Sandison, 1955). Eight initial items were devised (Table 1), out
of which two were ‘negative’ items that required reverse scoring.
Items were rated using a visual analogue scale (VAS) (0–100,
with incremental units of one) with zero defined as ‘No, not more
than usually’, and 100 defined as ‘Yes, entirely or completely’.
Five experts (W Richards, R Watts, R Carhart-Harris, J Rucker
and L Roseman) assessed the items and revised them if needed.
Below are selected quotes that helped inform the construction of
EBI items. These derive from interviews with patients (Watts
et al., 2017) in our recent psilocybin for treatment-resistant
depression trial (Carhart-Harris et al., 2017a). The quotes are
from the qualitative analysis of Watts et al. (2017), although most
were not included in that study.
‘It felt like a relief, I was getting so emotional, I could feel it
all coming out’
‘One emotional song, and I lost control, the song was so sad I
started crying uncontrollable, and was terrified by the depth
of emotions’
‘It was an emotional purging. The weight and anxiety and
overwhelming depression have been lifted’
‘It was an uncomfortable experience and it got to the point
where I got really really angry with it, like something snapped
inside my head, and rather than be afraid of it I challenged it
and at that point it kind of vanished, it went away’
‘I was weeping, tears were flowing out of me. It wasn’t a
painful crying, it was like turning on the taps, like a washing,
a washing out.’
‘There was a lot of sadness, really really deep sadness: the loss
the grief, it was love and sadness together, and letting go, I could
feel the grief and then let it go because holding onto it was
hurting me, holding me back. It was a process of unblocking’
‘Excursions into grief, loneliness and rage, abandonment.
Once I went into the anger it went ‘pouf’ and evaporated. I got
the lesson that you need to go into the scary basement, once
you get into it, there is no scary basement to go into [anymore]’
‘I had lost my ability to grieve and cry. [During the dosing
session] I cried and that was a cathartic experience for me, a
very welcoming sweet experience’.
Other measures
MEQ (Pahnke etal., 1970; Pahnke and Richards, 1966). The
MEQ was originally developed by Walter Pahnke and Bill Rich-
ards based on the anthropological research and theoretical writ-
ings of philosopher Walter Stace (1960). Stace studied reports of
mystical-type experiences occurring in a variety of religions and
identified common experiential components which he argued are
universal, i.e. culturally independent and unspecific to any par-
ticular religion or philosophical framework (as in Maslow’s peak
experience (Maslow, 1959; Maslow, 1964), and Huxley’s Peren-
nial Philosophy (Huxley, 1945)). The MEQ has been revised
since its original conception and now includes 30 questions
(MacLean et al., 2012) rated according to a five-point Likert
scale. It is divided into four subscales: (a) Mystical - which
includes arguably the core features of mystical-type experience:
named ‘unity’, ‘noetic’ and ‘sacredness’; (b) Positive-mood; (c)
Transcendence of time and space; and (d) Ineffability. The total
MEQ score is calculated as the average of all 30 items and then
multiplied by 20 to provide a 0–100 value.
CEQ. The CEQ was recently developed to measure the challeng-
ing experience (Barrett et al., 2016). The CEQ is derived from
‘challenging’ items from other psychedelic questionnaires: Hallu-
cinogen Rating Scale (HRS) (Strassman et al., 1994), Altered State
Table 1. Factor loadings from factor analysis of eight Emotional Breakthrough Inventory (EBI) items.
Item Factor 1 Factor 2
I faced emotionally difficult feelings that I usually push aside. 0.788 0.192
I experienced a resolution of a personal conflict/trauma. 0.896 −0.044
I felt able to explore challenging emotions and memories. 0.866 −0.076
I was resisting and avoiding challenging feelings throughout, without breakthrough. 0.260 0.786
I had an emotional breakthrough. 0.872 −0.151
I was able to get a sense of closure on an emotional problem. 0.889 −0.185
I felt emotionally stuck throughout, without breakthrough. 0.249 0.845
I achieved an emotional release followed by a sense of relief. 0.848 −0.194
The extraction method was principal component analysis (PCA). The six bold Items in Factor 1 reflect the final version of the EBI. The remaining bold items in Factor 2
where not used in the final version of EBI. Factor loadings >0.5 are in bold (n=379).
4 Journal of Psychopharmacology 00(0)
of Consciousness questionnaire (ASC) (Dittrich, 1975, 1998), and
States of Consciousness Questionnaire (SOCQ) (Griffiths et al.,
2006; Pahnke et al., 1969). The CEQ has 26 questions, five-point
Likert scale, and is divided into seven dimensions: (a) Isolation, (b)
Grief, (c) Physical distress, (d) Fear, (e) Insanity, (f) Paranoia, and
(g) Death. Total CEQ score was calculated as the average of all
items and then multiplied by 20 to provide a 0–100 value.
WEMWBS. The WEMWBS (Tennant et al., 2007) was designed to
measure the psychological well-being of a population. WEMWBS
has 14 questions scored using a five-point Likert scale. Scores
reflect feelings and thoughts in the two weeks prior to answering
the questionnaire. In the present study, the WEMWBS was used to
observe potential changes in well-being two weeks after drug intake
compared to baseline. Many of the participants had high baseline
WEMWBS scores – which created a potential ceiling effect limit-
ing scope for the predicted increases in well-being. We therefore
restricted the present analysis to just those subjects who had rela-
tively low baseline well-being scores (⩽45, n=75) (Taggart et al.,
2015) and therefore greater potential for change (normative data
based on the general population in England and Scotland showed a
mean WEMWBS score of 50.7 (95% confidence interval (CI):
50.3–51.1)).
Drug type. Participants were asked what specific psychedelic
they took. Options included: (a) psilocybin/magic mushrooms/
truffles, (b) LSD/1P-LSD, (c) ayahuasca, (d) DMT/5-5-MeO-
DMT, (e) Salvia divinorum, (f) mescaline, (g) iboga/ibogaine or
(h) the option to give a free answer.
Drug dose. Drug dose was assessed using a previously imple-
mented approach of estimating dosage in relation to LSD equiva-
lents. The rationale for this is to provide a reference-standard dose
that can be compared across different psychedelics (Nour et al.,
2016). Options were: a low dose (equivalent to no more than 50
μg of LSD), a moderate dose (equivalent to no more than 100 μg
of LSD), a high dose (equivalent to no more than 200 μg of LSD),
a very high dose (equivalent to no more than 300 μg of LSD), or
an extremely high dose (equivalent to more than 300 μg of LSD).
Therapeutic intention. At pre-drug baseline, participants
answered the question ‘Can you indicate what your motives are
to undergo a psychedelic session/ceremony/experience?’ A num-
ber of intentions were presented, and participants scored each of
them on a four-point Likert scale with the options: ‘not at all,’
‘somewhat,’ ‘moderately,’ or ‘very much.’ For this analysis we
chose two intentions of interest as potential predictors of EBI
scores: the intention to have the experience for (a) ‘Therapeutic/
personal growth’, and (b) ‘To confront difficult emotions’.
Therapeutic setting. Participants answered ‘yes’ or ‘no’ to the
question ‘Was the setting designed and/or prepared with a thera-
peutic objective in mind?’ We hypothesised that those who
answered ‘yes’ here would have higher EBI scores.
Factor analysis and definition of EBI
Scores for the original eight EBI items were subjected to an
exploratory factor analysis using principal component analysis
(PCA). The appropriate number of factors to be extracted was
determined by the scree plot criterion (Cattell, 1966). The PCA
yielded two factors (Table 1), out of which only factor 1 with six
items was used in further analysis. The internal consistency of
the six items was assessed with Cronbach’s alpha (Cronbach,
1951).
Discriminant validity
In order to test whether the EBI, and the construct it is intended
to sample, is significantly different from the constructs indexed
by the MEQ and CEQ, the items of all of the questionnaires were
entered into one factor analysis (PCA, 62 items). If EB, and the
EBI that samples EB, is insufficiently different from the other
questionnaires and the constructs they sample, then the PCA
would have been expected to yield just two factors – one contain-
ing items of the MEQ and the other containing items from the
CEQ, with EBI items loading onto one or both of these two fac-
tors. If, however, as predicted, the EBI can be discriminated from
the MEQ and CEQ, then the PCA would be expected to discover
three independent factors, one of which would contain items of
the EBI. A correlation matrix including the EBI and subdimen-
sions of MEQ and CEQ was also calculated to further explore
similarities and differences between the three questionnaires and
their components.
Predictive validity – changes in well-being
Pearson correlation of the EBI versus ΔWEMWBS was calcu-
lated to test whether the EBI could serve as a predictor of
clinical changes (n=75). Furthermore, a multiple regression
was calculated with ΔWEMWBS as the dependent variable
and the EBI, MEQ and CEQ as independent variables (n=75).
Beta coefficients were calculated for each of the question-
naires to assess the contribution of each of the questionnaires
to explaining changes in the dependent variable (ΔWEMWBS).
If significant beta coefficients were found for scores on all of
the questionnaires, this would demonstrate the significant
added value of each of the three questionnaires and the vari-
ance they can explain when combined. We hypothesised that
the beta coefficients of EBI and MEQ would be positive pre-
dictors of changes (increases) in WEMWBS scores whereas
CEQ scores would be negative predictors of changes in
well-being.
Results
Demographics
See Table 2 for the demographics of 379 participants who com-
pleted EBI and of a subsample of 75 participants with
WEMWBSbaseline⩽45.
Factor structure
The eight original EBI items were entered into a PCA. The
Kaiser-Meyer-Olkin (KMO) measure of sampling adequacy
was found to be 0.877, and Bartlett’s test of sphericity was sig-
nificant (χ2(28) =2005.9, p<0.0001) confirming that the data
was suitable for factor analysis (Budaev, 2010). Inspection of
the scree plot using Cattell’s criterion (Cattell, 1966) supported
Roseman et al. 5
a two-factor model (Table 1). The first component explained
57.1% of the variance and the second explained 18.3%. Other
components explained <8% of the variance. Commonality val-
ues (the variance of a variable which is explained by the fac-
tors) ranged from 65.7–82.5%. Factor 1 comprised of six items,
and factor 2 comprised of the two negative, reverse scored
items. Originally, we theorised that all items would load into
one single factor with the negative items negatively loading on
to this. Results revealed that this is not the case, however, and
instead the two negative items load onto a sufficiently distinct
factor. We therefore decided not to use these two negative items
in the final version of EBI.
Internal consistency
After discarding the two negative items, the resulting six-item EBI
displayed a very high internal consistency (Cronbach’s
alpha=0.932) (Cronbach, 1951). The average of the six items
showed a high correlation with factor 1 score (r=0.996, p<0.0001)
and therefore the average of the six items was used as the total EBI
score in further analysis. The mean of EBI scores was significantly
higher than 0 (EBI=43±31.5, skewness=0.165, kurtosis=−1.3,
p<0.0001, one sample t-test, n=379). The mean MEQ score was
57±22.63. The mean CEQ score was 19.7±16.4. See violin plots
(Hintze and Nelson, 1998) of EBI, MEQ and CEQ in Figure 1.
Table 2. Demographics.
Total n=379 n=75
Gender Male 252 (66.5%) 57 (76%)
Female 97 (25.6%) 18 (24%)
Other 2 (0.5%) 0
Blank 28 (7.4%) 0
Age 30.6±11.0 29±9.4
Educational level Left school before age 16 years without qualifications 7 (1.8%) 3 (4%)
Some high school/GCSE level (in UK) 23 (6.1%) 4 (5.3%)
High school diploma/A-level education (in UK) 47 (12.4%) 10 (13.3%)
University (or equivalent) 74 (19.5%) 18 (24%)
Bachelor’s degree (or equivalent) 121 (31.2%) 29 (38.7%)
Post-graduate degree (e.g. masters or doctorate) 79 (20.1%) 11 (14.7%)
Blank 28 (7.4%) 0
Employment status Student 124 (32.7%) 17 (22.7%)
Unemployed 33 (8.7%) 14 (18.7%)
Part-time job 55 (14.5%) 16 (21.3%)
Full-time job 133 (35.1%) 27 (36%)
Retired 6 (1.5%) 1 (1.3%)
Blank 28 (7.4%) 0
Nationality United Kingdom 74 (19.5%) 19 (25.3%)
United States of America 97 (25.6%) 21 (28%)
Denmark 42 (11.1%) 4 (5.3%)
Germany 21 (5.5%) 0
Canada 13 (3.4%) 5 (6.6%)
Other (38 other nationalities) 104 (27.4%) 26 (34.8%)
Blank 28 (7.4%)
Psychiatric history Has been diagnosed with at least one psychiatric
illness in the pasta
116 (30.6%) 38 (50.7%)
Never been diagnosed with a psychiatric illness 235 (62%) 37 (49.3%)
Previous psychedelic drug use Never (psychedelic naïve) 42 (11.1%) 11 (14.6%)
Once 20 (5.3%) 7 (9.3%)
2–5 times 71 (18.7%) 22 (29.3%)
6–10 times 54 (14.2%) 15 (20%)
11–20 times 57 (15%) 7 (9.3%)
21–50 times 63 (16.6%) 8 (10.6%)
51–100 times 19 (5%) 4 (5.3%)
More than 100 times 25 (7%) 1 (1.3%)
Blank 28 (7.4%)
Absolute frequencies and means±standard deviations are presented in the table. Numbers in the brackets show the percentages of the absolute frequencies. The column
with n=379 is the whole population in this paper, while the column with n=75 is of the subpopulation with Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS)⩽45.a
Psychiatric illnesses include major depressive disorder, bipolar disorder, schizophrenia, anxiety disorder, substance abuse disorder, alcohol dependence, hallucinogen
persisting perception disorder, psychotic disorder, personality disorder, attention deficit hyperactivity disorder, obsessive compulsive disorder and eating disorder.
6 Journal of Psychopharmacology 00(0)
Predictive validity – dose, therapeutic
intention and setting
As predicted, EBI scores significantly (positively) correlated
with (estimated) drug dose (rs=0.192, p=0.0001, one-tail, n=379).
Baseline ratings of therapeutic intention and ratings of willing-
ness to confront difficult emotions significantly correlated (posi-
tively) with EBI scores (rs=0.256 and rs=0.279, respectively,
p<0.0001, one-tail, n=351). Participants who endorsed the view
that the setting for their experience was designed with a therapeu-
tic objective in-mind had higher EBI scores (EBI=47.9±30.1,
n=144) than those who felt the setting for their experience was
not therapeutic in nature or design (EBI=31.6±29.1, n=168)
(p<0.0001, Cohen’s d=0.55, independent samples t-test,
one-tail).
Discriminant validity
To demonstrate that the EBI is a novel measure that can be dis-
criminated from the MEQ and CEQ, all of the 62 items from
MEQ, CEQ and EBI were entered into a single factor analysis
(PCA) (Table 3). The KMO measure of sampling adequacy was
0.941, and Bartlett’s test of Sphericity was significant
(χ2(1891)=19829, p<0.0001) confirming that the data was suitable
for factor analysis (Budaev, 2010). Inspection of the scree plot
using Cattell’s criterion (Cattell, 1966) supported a model of
three factors. The first component explained 31.3% of the vari-
ance, the second explained 15.4% of the variance, and the third
explained 6.1% of the variance. Other components explained
<4% of the variance in the sample. Commonality values ranged
from 43.7–81.5%. The first factor contained high loadings from
MEQ items, and relatively high loading from EBI items as well.
The second factor contained high loadings from CEQ items
alone, and the third factor contained high loading from EBI items
alone (without any MEQ or CEQ items). These results suggest
that for some subjects, EB was accompanied by mystical-type
phenomena (and vice versa), whilst for others, EB was distinct
from either classical challenging and/or mystical-type phenom-
ena. Note that the relatively low percentage of variance explained
by component 3 is probably due to the relatively few EBI items
when compared with the MEQ and CEQ (i.e. six in the EBI ver-
sus 26 and 30 the CEQ and MEQ, respectively).
A correlation matrix containing all of the EBI items plus sub-
scales of the MEQ and CEQ is presented in Figure 2. It is appar-
ent that the EBI correlates strongly with all MEQ dimensions and
also with the grief dimension of CEQ (a relationship between
EBI and grief is also suggested in the factor analysis (Table 3)).
Correlations between a given subscale of the MEQ and its other
subscales are higher than those with the EBI, suggesting that
despite some commonalities, the EBI and MEQ are still measur-
ing sufficiently distinct phenomena.
Predictive validity – changes in well-being
The difference in WEMWBS from baseline (38.8±5.3) to two
weeks after the experience (47.9±7.2) was significant (Cohen’s
d=1.44, p<0.0001, n=75, paired sample t-test). Emotional break-
through scores significantly correlated with changes in well-
being (ΔWEMWBS) two weeks after the psychedelic experience
(compared with well-being scores at baseline), r=0.294, p=0.005,
one-tail, n=75. A multiple regression analysis with ΔWEMWBS
as dependent variable and EBI, MEQ and CEQ values as inde-
pendent variables yielded a strong predictive model (r=0.45,
p=0.0005, one-tail, n=75). The standardised beta coefficients for
the EBI, MEQ and CEQ were all significant, with the EBI per-
forming as well as the other measures (βEBI=0.29, p=0.017;
βMEQ=0.24, p=0.038; βCEQ=−0.35, p=0.002; one-tail).
Independent Pearson’s correlations between the MEQ and CEQ
and ΔWEMWBS were r=0.274, and r=−0.147, respectively. The
tolerance measures (collinearity) of EBI, MEQ and CEQ were
0.631, 0.634, 0.814, respectively (tolerance >0.2 means that the
independent variables are relatively independent from each
other). As a further exploratory analysis, the same regression
model was applied to the wider sample regardless of WEMWBS
baseline scores. Out of the total sample, 253 participants had
completed the WEMWBS at two weeks after the experience. The
difference in WEMWBS from baseline (49.5±8.6) to two weeks
after the experience (52.7±7.3) for this population was signifi-
cant as well though with smaller effect size (Cohen’s d=0.4,
p<0.0001, n=253, paired sample t-test). A multiple regression
analysis with ΔWEMWBS as dependent variable and EBI, MEQ
and CEQ values as independent variables for these 253 partici-
pants yielded a marginally significant result in the same direction
as the smaller subsample (r=0.153, p=0.059, one-tail, n=253).
The standardised beta coefficients for the EBI, MEQ and CEQ
were all marginally significant (βEBI=0.115, p=0.063;
βMEQ=0.075, p=0.15; βCEQ=−0.086, p=0.01; one-tail).
Independent Pearson’s correlations between the EBI, MEQ and
CEQ and ΔWEMWBS were r=0.119, r=0.106 and r=−0.019,
respectively. Overall, the results of the larger subsample of 253
participants were in a similar direction yet less significant com-
pared to the subsample of 75 participants, and this is probably
Figure 1. Violin plots of Emotional Breakthrough Inventory (EBI),
Mystical Experience Questionnaire (MEQ) and Challenging Experience
Questionnaire (CEQ). Total scores of each questionnaire are spread
along the y axis. Violin plots are similar to box plots but show also
probability density in different values (the width of the plot). The
white circle and the thick line are a boxplot in which the white circle is
the median and the thick line is the interquartile range (n=379).
Roseman et al. 7
Table 3. Factor analysis of Emotional Breakthrough Inventory (EBI), Mystical Experience Questionnaire (MEQ) and Challenging Experience
Questionnaire (CEQ). All of the 62 items of the EBI, MEQ and CEQ have been included in a principal component analysis (PCA) which resulted in
three factors. The first factor has high loadings of items from MEQ and EBI. The second factor has high loadings of items from CEQ. The third factor
has high loading of items from EBI. This analysis, together with the correlation matrix in Figure 2, reveals that EBI is discriminate from MEQ and
CEQ. Factor loadings >0.5 are in bold (n=379).
Questionnaire Subscale Question Factor 1 Factor 2 Factor 3
EBI I faced emotionally difficult feelings that I usually push aside. 0.524 0.306 0.528
I experienced a resolution of a personal conflict/trauma 0.543 0.036 0.656
I felt able to explore challenging emotions and memories. 0.552 −0.055 0.613
I had an emotional breakthrough. 0.585 0.041 0.631
I was able to get a sense of closure on an emotional problem. 0.515 −0.057 0.678
I achieved an emotional release followed by a sense of relief. 0.606 −0.104 0.576
MEQ Mystical 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.
0.755 −0.309 −0.009
Experience of pure being and pure awareness (beyond the world of sense
impressions).
0.776 −0.3 −0.057
Experience of oneness in relation to an ‘inner world’ within. 0.789 −0.257 −0.056
Experience of the fusion of your personal self into a larger whole. 0.778 −0.271 −0.055
Experience of unity with ultimate reality. 0.801 −0.284 −0.061
Feeling that you experienced eternity or infinity. 0.761 −0.191 −0.127
Experience of oneness or unity with objects and/or persons perceived in
your surroundings.
0.65 −0.3 −0.078
Experience of the insight that ‘all is one’. 0.756 −0.321 −0.084
Awareness of the life or living presence in all things. 0.681 −0.337 −0.082
Gain of insightful knowledge experienced at an intuitive level. 0.705 −0.28 0.216
Certainty of encounter with ultimately reality. 0.682 −0.283 −0.02
You are convinced now, as you look back on your experience, that in it you
encountered ultimate reality.
0.653 −0.294 0.07
Sense of being at a spiritual height. 0.715 −0.299 0.007
Sense of reverence. 0.624 −0.255 −0.015
Feeling that you experienced something profoundly sacred and holy. 0.65 −0.243 −0.008
Positive
mood
Experience of amazement. 0.675 −0.291 −0.203
Feelings of tenderness and gentleness. 0.596 −0.374 0.091
Feelings of peace and tranquillity. 0.554 −0.521 −0.004
Experience of ecstasy. 0.522 −0.396 −0.097
Sense of awe or awesomeness. 0.654 −0.344 −0.144
Feelings of joy. 0.522 −0.451 −0.098
Time and
space
Loss of your usual sense of time. 0.632 −0.059 −0.234
Loss of your usual sense of space. 0.648 −0.049 −0.288
Loss of usual awareness of where you were. 0.547 0.058 −0.319
Sense of being ‘outside of’ time, beyond past and future. 0.742 −0.05 −0.204
Being in a realm with no space boundaries. 0.711 −0.181 −0.14
Experience of timelessness. 0.736 −0.114 −0.239
Ineffabil-
ity
Sense that the experience cannot be described adequately in words. 0.71 −0.045 −0.123
Feeling that you could not do justice to your experience by describing it
in words.
0.711 −0.074 −0.086
Feeling that it would be difficult to communicate your own experience to
others who have not had similar experiences.
0.649 −0.031 −0.086
CEQ Isolation Isolation and loneliness. 0.298 0.647 −0.001
Feeling of isolation from people and things. 0.255 0.623 −0.025
I felt isolated from everything and everyone. 0.252 0.628 −0.002
Grief Sadness. 0.356 0.542 0.365
Feelings of grief. 0.416 0.502 0.378
I felt like crying. 0.423 0.339 0.388
Feelings of despair. 0.396 0.662 0.118
Despair. 0.366 0.691 0.09
Emotional and/or physical suffering. 0.362 0.652 0.241
(Continued)
8 Journal of Psychopharmacology 00(0)
Questionnaire Subscale Question Factor 1 Factor 2 Factor 3
Physical
distress
Feeling my heart beating. 0.379 0.22 −0.093
Feeling my body shake/tremble. 0.324 0.301 −0.14
I felt shaky inside. 0.374 0.425 −0.115
I felt my heart beating irregularly or skipping beats. 0.348 0.184 −0.073
Pressure or weight in my chest or abdomen. 0.255 0.283 −0.012
Fear I had the feeling something horrible would happen. 0.414 0.686 −0.155
Experience of fear. 0.419 0.684 −0.188
Anxiousness. 0.298 0.61 −0.136
Panic. 0.414 0.655 −0.201
I felt frightened. 0.429 0.702 −0.158
Insanity Fear that I might lose my mind or go insane. 0.407 0.61 −0.203
I was afraid that the state I was in would last forever. 0.419 0.54 −0.235
I experienced a decreased sense of sanity. 0.414 0.48 −0.206
Paranoia I had the feeling that people were plotting against me. 0.233 0.31 −0.204
Experience of antagonism toward people around me. 0.167 0.368 −0.069
Death I had the profound experience of my own death. 0.501 0.229 −0.126
I felt as if I was dead or dying. 0.463 0.408 −0.161
Table 3. (Continued)
Figure 2. Correlation matrix of Emotional Breakthrough Inventory
(EBI), Mystical Experience Questionnaire (MEQ) subscales and
Challenging Experience Questionnaire (CEQ) subscales, and CEQ
subscales. High Pearson’s correlations are observed for EBI with MEQ
subscales, and with CEQGrief. Yet, correlations between any given MEQ
subscale and the other MEQ subscales are higher than with the EBI.
This analysis, together with the factor analysis in Table 3, suggest that
EBI is distinct from MEQ and CEQ (n=379).
CEQ-D: Death; CEQ-F: Fear; CEQ-G: Grief; CEQ-In: Insanity; CEQ-Is: Isolation;
CEQ-P: Paranoia; CEQ-Ph: Physical distress; MEQ-I: Ineffability; MEQ-M: Mystical;
MEQ-P: Positive mood; MEQ-ST: Transcendence of space and time.
due to a ceiling effect at the baseline of WEMWBS in the larger
subsample. These results confirm that each of the questionnaires
contribute added value to the model, whilst being significantly
distinct from each other. A natural conclusion from this is that a
prediction model containing measures of all three constructs will
perform better than a model that neglects any one of them.
Discussion
Here we sought to devise and carry out validation work on a new
scale intended to describe an important and hitherto under-quan-
tified component of the psychedelic experience, the EB. We
anticipate that this scale will serve as a useful ‘state’ predictor of
the longer-term psychological outcomes after a psychedelic
experience – supplementing already existing state predictor
measures such as the MEQ and CEQ. We call this new scale the
‘EBI’. Results revealed that (as measured by the EBI) emotional
breakthrough is dose dependent and sufficiently different from
the mystical-type and challenging experience as indexed by the
MEQ and CEQ respectively. Consistent with a major prior
hypothesis, we found that (like the MEQ) the EBI significantly
predicts post-psychedelic changes in well-being (greater EB,
greater increases in well-being) and we also discovered that the
EBI does not render either the CEQ or MEQ redundant but rather
a multi-factorial predictor model that combines all three meas-
ures performs better than any alternative that neglects any one of
them. The combined EBI, MEQ and CEQ model is able to predict
close to 20% of the variance in well-being changes after a psy-
chedelic experience, a not inconsiderable amount given the rela-
tively ‘well’ nature of this sample and uncontrolled study design.
We also found that both therapeutic intention and therapeutic set-
ting can predict the intensity of EB, suggesting that, as with other
components of the acute psychedelic experience, EB is highly
influenced by the context in which the psychedelic is taken
(Carhart-Harris et al., 2017b; Hartogsohn, 2016, 2017). Taken
together, these results support the addition of the EBI to the arse-
nal of tools used to quantitatively describe the psychedelic expe-
rience and predict its longer-term psychological effects.
Modern phenomenological analyses (Belser et al., 2017;
Gasser et al., 2014; Watts et al., 2017) and therapists’ accounts
(Bonny and Pahnke, 1972; Cohen, 1959; Crocket et al., 1963;
Eisner and Cohen, 1958; Fisher, 2015; Grof et al., 1980; Jensen,
1963; Katzenelbogen and Fang, 1953; Leuner, 1961; Martin,
Roseman et al. 9
1957; Richards, 2015; Sandison, 1955) have tended to recognise
the importance of EB within the context of psychedelic experi-
ences and psychedelic therapy; however, a validated quantitative
measure of this phenomenon is arguably overdue and there is a
significant contemporary need for it. Perhaps due to the relative
dearth of psychedelic research since the 1960s and a particular
bias common among those few research teams working within
the current resurgent era, contemporary researchers have tended
to place significant emphasis on the mystical-type experience, in
part due to well-replicated findings that its occurrence is predic-
tive of relevant psychological outcomes, such as improvements
in well-being (Haijen et al., 2018) changes in personality
(MacLean et al., 2011), and improvements in clinical outcomes
in patient populations (Roseman et al., 2017).
The present work has demonstrated the added value of meas-
uring EB for predicting subsequent psychological outcomes after
a psychedelic experience. However, are there other ‘state’ and
perhaps ‘contextual’ factors that are also important determinants
of longer-term responses to psychedelics – and might there be
alternative dependent variables that are differentially influenced
by state and contextual predictors? Indeed, these variables may
also interact in non-linear ways. We have previously emphasised
(Carhart-Harris et al., 2017b), and sought to measure and demon-
strate, the influence of contextual factors such as the presence of
others, associated therapeutic alliance, a therapeutic intention
and setting and a willingness to surrender or ‘let-go’ to the psy-
chedelic experience on longer-term psychological outcomes, and
found them to be important (Haijen et al., 2018). Like ‘state’ pre-
dictors of long-term responses, it is logical to see these factors as
mediators of the relevant changes, as they are temporal anteced-
ents of them. Other factors we predict may be important for influ-
encing long-term changes include psychological insight and
psychological integration. Insight is a phenomenon that may
occur acutely in a state-like fashion (like EB) but could only be
more protracted, crystallising in the days to weeks following a
psychedelic experience. Integration is another protracted phe-
nomenon that may have no clear end-point as such.
Much more work is needed to understand the neurobiology of
the entire psychedelic psychotherapy process and this will natu-
rally require brain imaging at various time points: before, during
and after a specific psychedelic experience. Further discussion of
this topic is beyond the remit of the present article, only to say
that there is some evidence that the magnitude of increased brain
entropy, a known biomarker of the psychedelic state, has been
found to be predictive of subsequent psychological changes
(increased trait ‘openness’) over a consistent time-scale as was
measured here in relation to well-being (Lebedev et al., 2016).
Finally, we advocate looking at other dependent variables
than just well-being. Well-being is a useful index of mental health
in general populations (Tennant et al., 2007) but it may be that
certain psychiatric disorders and/or symptom clusters behave dif-
ferently in their relation to predictor variables. This is something
we intend to investigate more fully in future analyses plus new
and on-going studies.
Our novel analysis is part of an effort to elucidate the impor-
tance of the psychological mechanism of psychedelics alongside
their pharmacological uses, and by doing so to emphasise the
importance of the context in which these drugs are taken. That is
to say that affirming that the experience mediates the clinical
outcomes, means that the regular clinical context will have to be
modified to accommodate psychedelics as an effective psychop-
harmacological intervention within psychiatry. On that note, there
is a lesson from history we would like to bring to readers’ attention
before closing: psychedelic therapy was once a relatively widely
practised intervention in Western psychiatry before opinion shifted
against it (Baum, 2016; Grinspoon and Bakalar, 1979). As the
pharmacological revolution in psychiatry gathered momentum in
the 1960s and the thalidomide scandal occurred at a related time,
regulations on experimental medicines tightened, as did the meth-
ods for assessing their safety and efficacy (Oram, 2012). Within
this climate, some efforts were made to extricate the basic pharma-
cological action of LSD from the psychotherapeutic manner in
which it was typically administered, e.g. by giving the drug in a
psychologically ‘sterile’ environment (Ludwig, 1985). In at least
one published study, patients treated with LSD were placed in a
belt that restrained them to their bed (Johnson et al. 1969).
Unsurprisingly, such efforts to ‘neutralise’ context (which is, of
course, a misnomer) tended to reveal that LSD without contextual
support does not nearly have the same therapeutic value and safety
profile as LSD given with therapeutic support (Oram, 2012, 2014).
These results, combined with the spread of unfounded but none-
theless affecting misinformation about LSD (Dishotsky et al.,
1971) plus a tightening of legislation on drugs of potential misuse,
best exemplified by the 1970 Controlled Substances Act (1970),
signalled the demise of psychedelic psychotherapy. The present
study’s analyses confirm the findings of other analyses (Dimascio
and Klerman, 1960; Haijen et al., 2018; Hyde, 1960; Lasagna,
1963; Leary et al., 1963; Studerus et al., 2012) that context is an
essential component of the psychedelic model (Carhart-Harris
et al., 2017b; Hartogsohn, 2017; Leary et al., 1963) and that if one
wishes to promote a positive therapeutic response to a psychedelic,
then heeding and optimising the role of certain contextual compo-
nents is entirely necessary, whereas neglecting them is bad practice
if not unethical. Our hope is that psychedelic therapy of the future
can be done in a way and a context that encourages and allows the
free release of emotion, e.g. using tools such as music (Barrett
et al., 2018; Bonny and Pahnke, 1972; Kaelen et al., 2017),
empathic listening and purposefully designed supportive environ-
ments, even if this presents a significant challenge to the conven-
tions of mainstream medicine:
[Practicing psychedelic therapy here] has transformed the
entire hospital, because the whole atmosphere engendered by
LSD has spread throughout the hospital and, in fact, forms an
essential part of the hospital culture. If LSD is given in a large
institutional setting, treatment will be ineffective unless this
transformation has occurred.
British psychiatrist Ronald Sandinson (1916–2010) cited in
Abramson (1960: 15)
Three limitations of the present study should be noted. First, the
present study’s population contained mostly healthy experienced
psychedelic users, and therefore the results do not necessarily
apply to clinical population (Haijen et al., 2018). In these users
the outcomes in well-being might be related to the expectation
build around psychedelic use in the psychedelic culture and lit-
erature. Furthermore the pharmacological mechanism of psych-
edelics might be different in these users due to greater exposure
to this class of drugs. To improve translational relevance, future
10 Journal of Psychopharmacology 00(0)
studies should use the EBI in clinical populations to assess its
ability to predict changes in clinically recognised phenomena,
such as depressive symptoms and anxiety. The prediction model
of changes in well-being predicted only 20% of the variance.
However, we do expect this model to perform better in a clinical
trial and in a controlled environment. Second, the study has relied
on self-reports of drugs, doses and timing, which are not as accu-
rate as in laboratory studies. Psychedelics that are sold in the
market are unreliable in many cases and one cannot be sure
which drug and what dose was used. Third, there was limited
analysis of convergent validity. Although there is clearly some
overlap with the MEQ, we are not aware of any other question-
naires that measure a construct closely related to EBI. One way
to address this in the future might be to compare EBI scores with
quantitative outcomes from qualitative interviews, to assess
whether there is some correspondence. A better demonstration of
the convergent validity of the EBI will serve to further strengthen
its construct validity (Campbell and Fiske, 1959).
In conclusion, EB is an essential component of psychedelic-
assisted therapy, and therefore should be measured in future
experimental medicine studies and clinical trials with psyche-
delics, alongside measures of peak and challenging experiences.
Quantifying the psychological mechanism of psychedelic-
assisted therapy is essential as psychedelic-assisted therapy is
rightly both a pharmacological and psychological intervention.
The predictive value of peak experiences is well-established
within this context, and now the importance of EBs can be better
researched and potentially supported as well. Furthermore, based
on qualitative studies (Belser et al., 2017; Gasser et al., 2014;
Watts et al., 2017) and a broader awareness of the phenomenol-
ogy of the psychedelic experience, we believe there is scope for
additional quantitative measures (e.g. of psychological insight) to
be developed, so that a fuller understanding of the psychological
and neurobiological mechanism of psychedelic (mind-revealing)
therapy can be appreciated and utilised for positive ends.
Acknowledgements
The authors would like to acknowledge Alex Belser, his Interdisciplinary
Conference on Psychedelics Research (ICPR) talk in 2016 served as a
catalyst for the creation of EBI (Belser, 2016).
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to
the research, authorship, and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the
research, authorship and/or publication of this article: LR is funded by
Imperial College President’s Scholarship Scheme and by a donation from
Albert Hohohm. MK is funded by Wavepaths. RW is funded by the Alex
Mosley Charitable Trust, RCH is funded by the Alex Mosley Charitable
Trust and Ad Astra Chandaria Foundation.
ORCID iDs
Leor Roseman https://orcid.org/0000-0001-9990-6029
Robin Carhart-Harris https://orcid.org/0000-0002-6062-7150
References
Abramson HA (1960) The Use of LSD in Psychotherapy: Transactions.
New York: Josiah Macy, Jr. Foundation.
Barrett FS, Bradstreet MP, Leoutsakos J-MS, et al. (2016) The Chal-
lenging Experience Questionnaire: Characterization of challenging
experiences with psilocybin mushrooms. J Psychopharmacol 30:
1279–1295.
Barrett FS, Preller KH and Kaelen M (2018) Psychedelics and music:
Neuroscience and therapeutic implications. Int Rev Psychiatry 1–13.
Baum D (2016) Legalize It All: How to win the war on drugs. Harper’s
Magazine. Available at: https://harpers.org/archive/2016/04/legal-
ize-it-all/ (accessed 28 November 2018).
Belser A (2016) Real, Relational, and Embodied: The First Qualitative
Study of Patient Experiences of Psilocybin-Assisted Psychotherapy.
In: Interdisciplinary Conference on Psychedelics Research (ICPR),
6 June 2016. Amsterdam. Youtube–Available at: https://www.you-
tube.com/watch?v=DUYDjV8lQxo
Belser AB, Agin-Liebes G, Swift TC, et al. (2017) Patient experiences
of psilocybin-assisted psychotherapy: An interpretative phenomeno-
logical analysis. J Humanist Psychol 57: 354–388.
Bogenschutz MP, Forcehimes AA, Pommy JA, et al. (2015) Psilocybin-
assisted treatment for alcohol dependence: A proof-of-concept study.
J Psychopharmacol 29: 289–299.
Bonny HL and Pahnke WN (1972) The use of music in psychedelic
(LSD) psychotherapy. J Music Ther 9: 64–87.
Breuer J and Freud S (1895) Studies on Hysteria. London: Hachette UK.
Budaev SV (2010) Using principal components and factor analysis in
animal behaviour research: Caveats and guidelines. Ethology 116:
472–480.
Campbell DT and Fiske DW (1959) Convergent and discriminant valida-
tion by the multitrait-multimethod matrix. Psychol Bull 56: 81.
Carbonaro TM, Bradstreet MP, Barrett FS, et al. (2016) Survey study
of challenging experiences after ingesting psilocybin mushrooms:
Acute and enduring positive and negative consequences. J Psycho-
pharmacol 30: 1268–1278.
Carhart-Harris R, Bolstridge M, Day C, et al. (2017a) Psilocybin with
psychological support for treatment-resistant depression: Six-month
follow-up. Psychopharmacology 235(2): 399–408.
Carhart-Harris R, Roseman L, Haijen E, et al. (2017b) Psychedelics
and the essential importance of context. J Psychopharmacol 32(7):
725–731.
Carhart-Harris RL (2018) Serotonin, psychedelics and psychiatry. World
Psychiatry 17: 358–359.
Cattell RB (1966) The scree test for the number of factors. Multivariate
Behav Res 1: 245–276.
Cohen S (1959) The therapeutic potential of LSD-25. In: Featherstone
RM and Simon A (eds) A Pharmacologic Approach to the Study of
the Mind. Springfield, Ill.: Thomas, pp. 251–257.
Controlled Substances Act (1970) Pub. L. No. 91-513, 84 Stat. 1236
(codified as amended at 21 U.S.C. § 812 (2012). HeinOnline.
Crocket RW, Sandison RA and Walk A (1963) Hallucinogenic Drugs
and Their Psychotherapeutic Use. London: HK Lewis.
Cronbach LJ (1951) Coefficient alpha and the internal structure of tests.
Psychometrika 16: 297–334.
Dakwar E, Anerella C, Hart C, et al. (2014) Therapeutic infusions of
ketamine: Do the psychoactive effects matter? Drug Alcohol Depend
136: 153–157.
Dimascio A and Klerman GL (1960) Experimental human psycho-
pharmacology: The role of non-drug factors. In: Sarwer-Foner GJ
(ed.) The Dynamics of Psychiatric Drug Therapy. Springfield, Ill.:
Thomas, pp. 56–84.
Dishotsky NI, Loughman WD, Mogar RE, et al. (1971) LSD and genetic
damage. Science 172: 431–440.
Dittrich A (1975) Zusammenstellung eines Fragebogens (APZ) zur
Erfassung abnormer psychischer Zustände [Construction of a ques-
tionnaire (APZ) for assessing abnormal mental states]. Z Klin Psy-
chol Psychiatr Psychother 23: 12–20.
Dittrich A (1998) The standardized psychometric assessment of altered
states of consciousness (ASCs) in humans. Pharmacopsychiatry 31:
80–84.
Roseman et al. 11
Dyck E (2006) ‘Hitting highs at rock bottom’: LSD treatment for alcohol-
ism, 1950–1970. Soc Hist Med 19: 313–329.
Eisner BG and Cohen S (1958) Psychotherapy with lysergic acid diethyl-
amide. J Nerv Ment Dis 127: 528–539.
Erritzoe D, Roseman L, Nour M, et al. (2018) Effects of psilocybin
therapy on personality structure. Acta Psychiatr Scand 138: 368–
378.
Fisher FM (2015) Therapy with Substance: Psycholytic Psychotherapy in
the Twenty First Century. London: Muswell Hill Press.
Frederking W (1955) Intoxicant drugs (mescaline and lysergic acid dieth-
ylamide) in psychotherapy. J Nerv Ment Dis 121: 262–266.
Garcia-Romeu AP, Johnson MW and Griffiths RR (2014) Examining the
psychological mechanisms of psilocybin-assisted smoking cessation
treatment: A pilot study. Drug Alcohol Depend 140: e66.
Gasser P, Kirchner K and Passie T (2014) LSD-assisted psychotherapy
for anxiety associated with a life-threatening disease: A qualitative
study of acute and sustained subjective effects. J Psychopharmacol
29: 57–68.
Griffiths RR, Johnson MW, Carducci MA, et al. (2016) Psilocybin pro-
duces substantial and sustained decreases in depression and anxiety
in patients with life-threatening cancer: A randomized double-blind
trial. J Psychopharmacol 30: 1181–1197.
Griffiths RR, Richards WA, McCann U, et al. (2006) Psilocybin can
occasion mystical-type experiences having substantial and sustained
personal meaning and spiritual significance. Psychopharmacology
187: 268–283.
Grinspoon L and Bakalar JB (1979) Psychedelic Drugs Reconsidered.
New York: Basic Books.
Grof S (1975) Realms of the Human Unconscious: Observations from
LSD Research. London: Souvenir Press Ltd; 2016 Edition.
Grof S, Hofmann A and Weil A (1980) LSD Psychotherapy (The healing
potential of psychedelic medicine). Ben Lomond, CA: Multidisci-
plinary Association for Psychedelic Studies; 2008 Edition.
Haijen ECHM, Kaelen M, Roseman L, et al. (2018) Predicting responses
to psychedelics: A prospective study. Front Pharmacol 9: 897.
Hartogsohn I (2016) Set and setting, psychedelics and the placebo
response: An extra-pharmacological perspective on psychopharma-
cology. J Psychopharmacol 30: 1259–1267.
Hartogsohn I (2017) Constructing drug effects: A history of set and set-
ting. Drug Sci Policy Law 3: 2050324516683325.
Hintze JL and Nelson RD (1998) Violin plots: A box plot-density trace
synergism. Am Stat 52: 181–184.
Huxley A (1945) The Perennial Philosophy. Toronto: New Canadian
Library.
Hyde RW (1960) Psychological and social determinants of drug action.
In: GJ Sarwer-Foner (ed.) Dynamics of Psychiatric Drug Therapy.
Springfield: Thomas, pp. 297–315.
Jackson SW (1994) Catharsis and abreaction in the history of psychologi-
cal healing. Psychiatr Clin North Am 17: 471–491.
Jensen S (1963) Treatment of chronic alcoholism with lysergic acid
diethylamide. Can Psychiatr Assoc J 8: 182–188.
Johnson FG (1969) LSD in the treatment of alcoholism. American Jour-
nal of Psychiatry 126: 481–487.
Johnson MW, Garcia-Romeu A and Griffiths RR (2016) Long-term
follow-up of psilocybin-facilitated smoking cessation. Am J Drug
Alcohol Abuse 1–6.
Kaelen M, Giribaldi B, Raine J, et al. (2017) The hidden therapist: Evi-
dence for a central role of music in psychedelic therapy. Psychophar-
macology 235: 505–519.
Katzenelbogen S and Fang AD (1953) Narcosynthesis effects of sodium
amytal, methedrine and LSD-25. Dis Nerv Syst 14: 85–88.
Klavetter RE and Mogar RE (1967) Peak experiences: Investigation of
their relationship to psychedelic therapy and self-actualization. J
Humanist Psychol 7: 171–177.
Kurland AA, Grof S, Pahnke WN, et al. (1972) Psychedelic drug assisted
psychotherapy in patients with terminal cancer. J Thanatol 2(1–2):
644–691
Lasagna L (1963) The relation of drug induced changes to personality. In:
M. Rinkel (ed.) Specific and Non-specific Factors in Psychopharma-
cology. New York: Philosophical Library, pp. 114–129.
Leary T, Litwin GH and Metzner R (1963) Reactions to psilocybin
administered in a supportive environment. J Nerv Ment Dis 137:
561–573.
Lebedev AV, Kaelen M, Lovden M, et al. (2016) LSD-induced entropic
brain activity predicts subsequent personality change. Hum Brain
Mapp 37: 3203–3213.
Leuner H (1961) Psychotherapy with hallucinogens. Hallucinogenic
Drugs 67: 67–73.
Loizaga-Velder A (2013) A psychotherapeutic view on therapeutic
effects of ritual ayahuasca use in the treatment of addiction. MAPS
Bull 23: 36–40.
Ludwig AM (1985) Cognitive processes associated with ‘spontaneous’
recovery from alcoholism. J Stud Alcohol 46: 53–58.
MacLean JR, MacDonald DC, Byrne UP, et al. (1961) The use of LSD-25
in the treatment of alcoholism and other psychiatric problems. New
Haven: Laboratory of applied Biodynamics, Yale University.
MacLean KA, Johnson MW and Griffiths RR (2011) Mystical experi-
ences occasioned by the hallucinogen psilocybin lead to increases
in the personality domain of openness. J Psychopharmacol 25:
1453–1461.
MacLean KA, Leoutsakos JMS, Johnson MW, et al. (2012) Factor analy-
sis of the mystical experience questionnaire: A study of experiences
occasioned by the hallucinogen psilocybin. J Sci Study Relig 51:
721–737.
Martin AJ (1957) LSD (lysergic acid diethylamide) treatment of chronic
psychoneurotic patients under day-hospital conditions. Int J Soc Psy-
chiatry 3: 188–195.
Maslow AH (1959) Cognition of being in the peak experiences. J Genet
Psychol 94: 43–66.
Maslow AH (1964) Religions, Values, and Peak-Experiences. Colum-
bus: Ohio State University Press.
Nour MM, Evans L, Nutt D, et al. (2016) Ego-dissolution and psychedel-
ics: Validation of the ego-dissolution inventory (EDI). Front Hum
Neurosci 10: 269.
O’Reilly P and Funk A (1964) LSD in chronic alcoholism. Can Psychiatr
Assoc J 9: 258–261.
Oram M (2012) Efficacy and enlightenment: LSD psychotherapy and the
drug amendments of 1962. J Hist Med Allied Sci. Epub ahead of print
16 August 2012. DOI: 10.1093/jhmas/jrs050.
Oram M (2014) The trials of psychedelic medicine: LSD psychotherapy,
clinical science, and pharmaceutical regulation in the United States,
1949–1976. PhD Doctorate. University of Sydney, School of Philo-
sophical and Historical Inquiry, Department of History.
Osmond H (1957) A review of the clinical effects of psychotomimetic
agents. Ann N Y Acad Sci 66: 418–434.
Pahnke WN and Richards WA (1966) Implications of LSD and experi-
mental mysticism. J Religion Health 5: 175–208.
Pahnke WN, Kurland AA, Goodman LE, et al. (1969) LSD-assisted
psychotherapy with terminal cancer patients. Curr Psychiatr Ther
9: 144–152.
Pahnke WN, Kurland AA, Unger S, et al. (1970) The experimental use of
psychedelic (LSD) psychotherapy. JAMA 212: 1856–1863.
Richards WA (2015) Sacred Knowledge: Psychedelics and Religious
Experiences. New York: Columbia University Press.
Richards WA, Rhead JC, DiLeo FB, et al. (1977) The peak experience
variable in DPT-assisted psychotherapy with cancer patients. J Psy-
chedelic Drugs 9: 1–10.
Roseman L, Nutt DJ and Carhart-Harris RL (2017) Quality of acute psy-
chedelic experience predicts therapeutic efficacy of psilocybin for
treatment-resistant depression. Front Pharmacol 8: 974.
Ross S, Bossis A, Guss J, et al. (2016) Rapid and sustained symptom
reduction following psilocybin treatment for anxiety and depression
in patients with life-threatening cancer: A randomized controlled
trial. J Psychopharmacol 30: 1165–1180.
12 Journal of Psychopharmacology 00(0)
Sandison R (1955) LSD treatment for psychoneurosis: Lysergic acid
diethylamide for release of depression. Nurs Mirror 100: 1529–1530.
Schenberg EES (2018) Psychedelic-assisted psychotherapy: A paradigm
shift in psychiatric research and development. Front Pharmacol 9: 733.
Stace WT (1960) Mysticism and philosophy. London: Macmillan Pub-
lishers.
Strassman RJ, Qualls CR, Uhlenhuth EH, et al. (1994) Dose-response study
of N, N-dimethyltryptamine in humans: II. Subjective effects and pre-
liminary results of a new rating scale. Arch Gen Psychiatry 51: 98–108.
Studerus E, Gamma A and Vollenweider FX (2010) Psychometric evalu-
ation of the altered states of consciousness rating scale (OAV). PloS
One 5: e12412.
Studerus E, Gamma A, Kometer M, et al. (2012) Prediction of psilocybin
response in healthy volunteers. PloS One 7: e30800.
Taggart F, Stewart-Brown S and Parkinson J (2015) Warwick-Edinburgh
Mental Well-being Scale (WEMWBS) User Guide, Version 2. NHS
Health Scotland.
Tennant R, Hiller L, Fishwick R, et al. (2007) The Warwick-Edinburgh
mental well-being scale (WEMWBS): Development and UK valida-
tion. Health Qual Life Outcomes 5: 63.
Watts R, Day C, Krzanowski J, et al. (2017) Patients’ accounts
of increased ‘Connectedness’ and ‘Acceptance’ after psilocy-
bin for treatment-resistant depression. J Humanist Psychol 57:
520–564.
