The Challenging Experience Questionnaire: Characterization of challenging experiences with psilocybin mushrooms

This online survey study (n=1767) validated a questionnaire that can assess challenging experiences occasioned by psilocybin and other hallucinogens. The authors characterize the phenomenological profile of challenging experiences as consisting of grief, fear, death, insanity, isolation, physical distress, and paranoia and describe the relationship of these factors to meaningfulness, spiritual significance, and change in well-being. This questionnaire presents a useful tool for investigating how acute adverse reactions to psilocybin affect long-term outcomes, such as well-being.


“Acute adverse psychological reactions to classic hallucinogens (“bad trips” or “challenging experiences”), while usually benign with proper screening, preparation, and support in controlled settings, remain a safety concern in uncontrolled settings (such as illicit use contexts). Anecdotal and case reports suggest potential adverse acute symptoms including affective (panic, depressed mood), cognitive (confusion, feelings of losing sanity), and somatic (nausea, heart palpitation) symptoms. Responses to items from several hallucinogen-sensitive questionnaires (Hallucinogen Rating Scale, the States of Consciousness Questionnaire, and the Five-Dimensional Altered States of Consciousness questionnaire) in an Internet survey of challenging experiences with the classic hallucinogen psilocybin were used to construct and validate a Challenging Experience Questionnaire. The stand-alone Challenging Experience Questionnaire was then validated in a separate sample. Seven Challenging Experience Questionnaire factors (grief, fear, death, insanity, isolation, physical distress, and paranoia) provide a phenomenological profile of challenging aspects of experiences with psilocybin. Factor scores were associated with difficulty, meaningfulness, spiritual significance, and change in well-being attributed to the challenging experiences. The factor structure did not differ based on gender or prior struggle with anxiety or depression. The Challenging Experience Questionnaire provides a basis for future investigation of predictors and outcomes of challenging experiences with classic hallucinogens.”

Authors: Frederick S. Barrett, Matthew P. Bradstreet, Jeannie-Marie S. Leoutsakos, Matthew W. Johnson & Roland R. Griffiths



Classic psychedelic hallucinogens such as psilocybin, LSD, mescaline, and DMT share a primary pharmacological site of action at the serotonin 2a (5HT2a) receptor and display striking similarities in their subjective effects.

Recent studies have examined the positive mental health outcomes, positive self-referential processing, altered social processing, visual imagery, personality change, and enduring positive changes in attitudes, mood and behavior occasioned by psychedelics. However, challenging psychological experiences during the acute effects of psychedelics are not uncommon.

Phenomenology of challenging psychedelic experiences

Researchers have conducted therapeutic research with LSD and mescaline, and have noted instances of fear, delusions, dissociation, depersonalization, and sympathetic nervous system responses. However, reports of psychosis lasting more than 48 h are exceedingly rare.

Acute adverse psychological reactions to classic hallucinogens (bad trips) are usually benign with proper screening, preparation, and support in controlled settings, but remain a safety concern in uncontrolled settings. A Challenging Experience Questionnaire was constructed and validated to assess challenging aspects of experiences with psilocybin.

A review of clinical literature and research literature on acute adverse effects of classic hallucinogens found that patients typically experienced frightening illusions and hallucinations, overwhelming anxiety or panic, confusion, aggression and possible violence, depression with suicidal ideation, gestures, or attempts, and fear.

Approximately 30% of participants in three highly controlled experimental studies experienced marked periods of anxiety or fear, while between 17 – 39% experienced paranoia. Only three out of 42 participants receiving up to a moderate dose reported prolonged symptoms.

Clinical and experimental literature on psychedelics suggests that challenging experiences may include fear, panic, paranoia, sadness or depressed mood, anger, cognitive effects, perceptual effects, and physiological symptoms.

Current assessments of challenging experiences

There are several questionnaires that assess the subjective effects of classic hallucinogens, but no comprehensive list of clearly defined sub-scales that separately measure the categories of challenging experience that are suggested by previous literature.

The HRS was developed explicitly as a means to quantify the subjective effects of classic hallucinogens. However, the affect, cognition, intensity, perception, somaesthesia, and volition sub-scales do not distinguish between very strong challenging experiences and very strong non-challenging experiences.

The OAV and 5DASC have been widely used in behavioral and neuroimaging research of pharmacologically and non-pharmacologically induced altered states of consciousness. The OAV sub-scale “dread of ego dissolution” (DED) covers a wide range of negative experiences, but does not address all possible dimensions of challenging experience.

Many instruments were used to assess subjective experience of hallucinogens, but all suffered from at least one of the shortcomings of the 5DASC and HRS, namely, lack of specificity, lack of content coverage, or lack of sensitivity to challenging experiences.

Why an assessment of dimensions of challenging experience is needed

In research contexts, acute adverse effects of psychedelics may be minimized and successfully managed with set (participant psychological state) and setting (interpersonal and physical environment). However, challenging experiences can still occur in the presence of substantially controlled and supportive conditions.

Little is known regarding the interdependence, causes, and consequences of the different categories of challenging experience. It would be useful to know whether there are reliable indicators that could be used to predict which category an individual will experience.

Psychedelics offer a tool for studying the biological basis of emotional experiences using modern neuroscientific tools such as brain imaging. However, a measurement instrument is lacking that can assess individual differences in challenging experiences during acute effects of psychedelics.

Aim of the current studies

In the following two studies, a Challenging Experience Questionnaire (CEQ) was constructed, and the factor structure and factor scores of the CEQ were established, replicated, and validated in stratified sub-samples.

Study 1

This study is a secondary analysis of data from an online survey of challenging experiences with psilocybin. The survey sample was stratified into two demographically matched groups, and a CEQ was developed using items from the HRS, 5DASC, and SOCQ.

A survey was administered to a sample of adults who had experienced a psilocybin-related challenging experience. Factorial invariance of the instrument was assessed across levels of gender and struggle with a psychiatric disorder that preceded the reported challenging experience.


The Bad Trip Survey was completed by 2085 participants. They were recruited via Internet advertisements, email invitation, and word of mouth, and were aged 18 – 70 years old at the time of the reported challenging experience. Participants who did not meet inclusion criteria were directed to an abbreviated version of the survey, and their data were not included in the analysis. Participants were also asked to refrain from completing the survey more than once.


Participants completed an online survey that included the HRS, 5-DASC, and SOCQ, among other questions. The CEQ was constructed from 64 items from the HRS, 5-DASC, and SOCQ, and demographic variables were assessed and used to generate two demographically matched strata.

The HRS is a 99-item instrument that assesses six general dimensions of subjective experience during an experience with a specified drug. Twenty-seven items were retained for the initial item pool for the CEQ.

The 5DASC is the latest version of the Altered States of Consciousness (APZ) questionnaire, which consists of 94 items. It was used to develop the CEQ, which consists of 13 items that assess impaired cognition and control and anxiety.

The SOCQ is a 100-item questionnaire that contains 43 items from the Mystical Experiences Questionnaire (MEQ43) and 57 items that were suggested by a sample of clinicians. The CEQ contains 24 distractor items that assess potentially challenging aspects of experiences with classic hallucinogens.

The overall impact of the challenging experience was assessed using a set of items that have been administered in laboratory studies of the acute and persisting effects of psilocybin.

Participants reported that their psilocybin session was similar to difficult or challenging experiences that occur on average once every 5 years, among the top 10 most difficult or challenging/meaningful experiences of their life, among the top five most difficult or challenging/meaningful experiences of their life, and the single most difficult/meaningful experience of their life.

Previous struggle with a psychiatric disorder was indicated by indicating whether or not you had struggled with anxiety, depression, substance use disorder, or “other psychiatric disorder”.

Demographic questions were asked, including age, gender, education, race, and total incidence of past hallucinogen use. Participants were also asked to rate the number of times they had used hallucinogens.


A total of 1767 participants were used for the analysis. They were matched on age, sex, education, race, and total incidence of past hallucinogen use, and demographic data were compared between strata using a two-sample t-test.

The latent structure of the items of the CEQ was identified using item analysis and exploratory factor analysis. A mixed correlation matrix was generated and a maximum likelihood factor extraction and oblimin rotation were conducted using the fa function in the psych toolbox in R.

An exploratory factor analysis was fit to the data to identify common factors. Iterative scale analyses were conducted on the remaining items to assess dimensionality and reliability of the scales, and an initial model for the CEQ was determined.

The resulting exploratory factor model was replicated using confirmatory factor analysis in a second stratum. A combination of fit indices was used to assess model fit, with “good fit” values of SRMR0.09, and CFI >0.90 indicating acceptable model fit.

Factorial invariance analysis is a test of whether a set of variables has a similar factor structure in different groups. It is conducted by performing a series of multiple-group confirmatory factor analyses, adding more constraints in each sequential model for parameters to be equal across groups.

Strong or strict factorial invariance provides evidence that the CEQ measures constructs in a similar fashion in each group being compared. This allows direct comparison of latent variable means between groups.

Factorial invariance was assessed using multiple-group confirmatory factor models with maximum likelihood estimation. A decrease in CFI, increase in SRMR, and increase in RMSEA between levels of factorial invariance indicates noninvariance.

A structural regression model was conducted to test the relationship between the CEQ and the overall impact of a challenging experience. The results provide evidence for the convergent validity of the CEQ.

Initial scale construction

Nine items were removed from the exploratory stratum because they were skew or kurtosis greater than 1.5. The remaining items were visually inspected to verify that the full range of responses had been utilized in each item.

An initial factor model was estimated, and a six-factor solution was found that had a cohesive qualitative interpretation. Items with no loading above 0.4 on any factor were discarded, and 12 additional items were removed, yielding a final set of 24 items.

A factor analysis was conducted on the 24 remaining items, and a factor structure was determined that explained 67% of the variance in the observed data.

In order to assess paranoia in challenging experiences with classic hallucinogens, a seventh factor was added to the CEQ, which consists of two items: feeling that people were plotting against you and experiencing antagonism toward people around you.

Model replication

A confirmatory factor model was fit to the mixed correlation matrix, with positive loadings of each item onto its intended factor, and all other item loadings equal to zero.

A 26-item, seven-factor confirmatory model was fit using the 24-item six-factor structure identified in exploratory analyses of the first stratum. Fit indices indicated acceptable model fit for both the initial 24-item six-factor structure of the CEQ and the additional two items for paranoia.

Factorial invariance of the CEQ

Factorial invariance was tested separately for two levels of sex and two levels of previous struggle with a psychiatric disorder. Fit indices indicated negligible change between all levels of factorial invariance.

Overall impact of the challenging experiences

The CEQ death factor was associated with a decrease in wellbeing attributed to the experience, and was positively associated with all other ratings of overall impact. The CEQ fear factor was negatively associated with ratings of spiritual significance and meaningfulness of the experience.

Study 2

In Study 1, the items comprising the CEQ were taken from three separate and extensive instruments. In Study 2, the 26-item CEQ was validated as a stand-alone instrument and used the same factor structure and regression results as in Study 1.


A total of 1052 participants were recruited through word of mouth and online advertisement, and completed an online survey exploring challenging experiences with psilocybin. Seventy-one participants were excluded based on the criteria specified in Study 1.


Demographics for participants in Study 1 are presented in Table 1, and chi-squared independence tests are used for all other demographic variables.

Twenty-six items were presented in fixed pseudorandom order in the CEQ, with the same response format for each item. The 5-DASC and HRS items were altered to better match the prose of the stand-alone CEQ.


Multiple-group confirmatory factor analyses were used to test for factorial invariance of the CEQ between Study 1 and Study 2. A structural equation model was fit to the Study 2 sample.


Study 2 differed from Study 1 on all demographic variables, including age, education, race, and ethnicity. Participants in Study 2 reported more experiences with classic hallucinogens, including psilocybin mushrooms.

Factor analysis indicated that the 26-item CEQ was invariant between Studies 1 and 2, with higher scores on fear and physical distress factors and lower scores on insanity and paranoia factors in Study 2.

The structural equation model indicated that factor scores on the CEQ were positively associated with ratings of change in wellbeing attributed to the experience, and negatively associated with ratings of spiritual significance of the experience.

General discussion

The CEQ was developed from responses to an Internet survey of challenging experiences, and the stand-alone CEQ was validated in responses to a separate Internet survey of challenging experiences.

Internal and external validity of the CEQ

The factor structure of the CEQ was identified in Study 1 and validated in Study 2. It was found to be invariant across gender and psychiatric illness.

Participants’ ratings of the degree of difficulty of the challenging experience were consistently positively associated with scores on the fear, grief, insanity, and death factors of the CEQ. Differences in factor scores between samples were observed in four scales.

A clinical definition of paranoia is “unfounded fears that others intend harm to the individual”. The CEQ paranoia scale contains one item that is consistent with this definition.

Challenging experiences and the overall impact of experiences with psilocybin

Previous studies have shown that moderate to high doses of psilocybin occasion experiences that are frequently rated in the top five most meaningful and spiritually significant experiences of a participant’s life. This study investigated the association between CEQ factor scores and the overall impact ratings of meaningfulness, spiritual significance, and change in well-being.

Scores on the fear factor were negatively associated with spiritual significance in both studies, while scores on the insanity factor were positively associated. A loss of self-referential processing during mystical experiences may be expected to correlate with both the meaningfulness and spiritual significance of an experience. However, scores on the death factor of the CEQ were negatively associated with change in well-being. While the experience of ego dissolution and mystical experience are positively associated with well-being, the ‘death’ factor of the CEQ is negatively associated with well-being. This may have implications for the therapeutic efficacy of psychedelics in clinical trials. Scores on the fear factor of the CEQ were associated with increased well-being attributed to challenging experiences.

Some discrepancies exist between Study 1 and Study 2 regarding the significant predictors of meaningfulness, spiritual significance, and change in well-being attributed to experiences. Paranoia was negatively associated with the rated difficulty of the experience in Study 1 but not Study 2, and physical distress was positively associated with change in well-being in Study 2.

The relationships between CEQ factor scores and ratings of the overall impact of challenging psychedelic experiences may be different for individuals with a different regard towards psychedelics, but consistencies were found between studies (e.g. the relationship between fear, grief, insanity, and death factor scores and rated difficulty of the experience).

Potential risk factors for challenging experiences

In Study 1, individuals who had previously struggled with a psychiatric disorder had significantly greater factor scores than those who had not, for all factors except for paranoia. However, it is not clear that such a generalization is warranted, as the current survey does not inform or address the frequency or likelihood of a challenging experience.

Psilocybin may be useful as a treatment for depression and anxiety secondary to a life-threatening cancer diagnosis, and there is a lower risk for psychological distress and suicidality in those who have endorsed having consumed a classic hallucinogen in the past.

Towards a model of challenging experiences

The CEQ provides a structure to consider the acute effects of challenging experiences, and may be used in prospective studies. Additional categories of challenging experiences have been suggested in the literature, such as the experience of kundalini energy or the experience of age regression.

The current findings deal primarily with challenging aspects of experiences with psilocybin, and the future studies may benefit from this understanding.


The CEQ may serve as a valuable tool for characterizing psychologically difficult aspects of experiences occasioned by psilocybin and, very likely, by other classic hallucinogens. It may also facilitate the optimization of therapeutic application of drugs within this class.

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