Pahnke’s ‘Good Friday Experiment’: a long-term follow-up and methodological critique

This methodological critique and long-term, between-subjects, follow-up study (n=16) challenges how the mystical experiences occasioned by psilocybin (30mg) were measured during Walter Pahnke’s infamous ‘Good Friday experiment’ (1963) on the basis of its imprecise questionnaire assessment and unsuccessful placebo blinding. However, all psilocybin subjects participating in the long-term follow-up, but none of the controls, still considered their original experience to have had genuinely mystical elements and to have made a uniquely valuable contribution to their spiritual lives even 27 years after.


Introduction: To investigate the potential of psychedelic drugs to facilitate mystical experience, W. Pahnke (1963) administered psilocybin or placebo to 20 White male Protestant divinity students before Good Friday services. The present study critiques the preparation phase of the experiment, Pahnke’s questionnaire for measuring mystical experience, and completeness of his reporting.

Methods: Between 1986 and 1989, the present author recorded personal interviews with 16 of the original Ss. All 16 were re-administered the 100-item questionnaire used for 6-mo follow-up in the original experiment. The original experiment found that psilocybin Ss who experienced a mystical experience would, after 6 mo, report a substantial amount of positive, and virtually no negative, persisting changes in attitude and behavior.

Results: The present study further supports these findings.”

Author: Rick Doblin


Cambridge, Massachusetts

Walter Pahnke administered small capsules to twenty Protestant divinity students on Good Friday, 1962, and determined that the persons who received psilocybin experienced the phenomena described by his typology of mysticism.

This paper is a methodological critique and long-term follow-up study of the “Good Friday Experiment”, which was conducted by Pahnke in 1962 for his Ph.D. in Religion and Society at Harvard University.

A follow-up study of the original experiment is of fundamental importance in evaluating the original experiment. It has been over 25 years since it has been legally possible to replicate or revise this experiment.

Nineteen out of the original twenty subjects were identified and located, and sixteen were interviewed. The six-month 100-item follow-up questionnaire was re-administered to all sixteen subjects.

One subject is deceased, one is unknown, one declined to participate citing concerns about privacy, and one interpreted Pahnke’s pledge of confidentiality to mean that the subjects should not talk about the experiment to anyone.

Seven out of ten of Pahnke’s original research assistants were interviewed for background information about the experiment.


Pahnke conducted extensive research over a period of four years to determine the most conducive environment for his experiment: a group of Christian divinity students in church during a Good Friday service.

Twenty white male Protestant volunteers were given a series of psychological and physical tests, and were matched with one another in a randomized controlled, matched group, double-blind experiment using an active placebo.

Three different methods were used to quantify the experiences of the subjects after Good Friday, including written descriptions, interviews and questionnaires. The results were compared to each other.

Pahnke secured permission to use Marsh Chapel from Rev. Howard Thurman, Boston University’s dynamic black chaplain, and set up a self-contained basement chapel.

Pahnke gave nicotinic acid to the controls who were expecting to receive psilocybin. This was done to potentiate suggestion.

Ten research assistants worked with five groups of four subjects to provide emotional support prior to and during the service.

As a precaution against bias, group leaders were told not to discuss specific aspects of the psychedelic or mystical experience. This was confirmed by all subjects in their long-term follow-up interviews.

The group leaders were given a pill prior to the service, but were not tape recorded or asked to fill out questionnaires. Pahnke himself refrained from having any personal experiences with any psychedelic drugs until after the experiment and follow-up had been completed.

Difficulties with the Double-Blind

The double-blind was successfully sustained through all phases of the experiment, including ingestion of the capsule. The group leaders were initially unable to distinguish whether subjects had received the psilocybin or the placebo.

All subjects who received psilocybin experienced powerful subjective effects, and were able to correctly determine whether they had received psilocybin or the placebo, even though they were never told which group they were in.

After about a half hour, I got this burning sensation, and I kept asking T.B. and Y.M. if they felt anything. They didn’t, so I kept concentrating on charting my course, but all I got was more indigestion and uncomfortable.

Nothing much more happened, and after 40 minutes or 45 minutes, T.B. said to me, “Those lights are unbelievable”. I looked at the candles and couldn’t see anything strange, but Y.M. said, “Yeah.”

The follow-up interviews showed that the experimental team did not deliberately use their knowledge of which pill the subjects had received to bias the results.

Many in positions of authority believe that randomized, double-blind, controlled clinical trials are the only basis for registering a drug, but this viewpoint is untenable, needlessly rigid, unrealistic, and at times unethical.

In certain participant-observer situations, the purpose might be to influence the system under investigation as much as possible, while still accounting for the variance within the system attributable to the several significant and relevant aspects of the investigator’s participant observation.

The loss of the double-blind made it impossible to determine the relative contributions of psilocybin and suggestion in producing the subjects’ reported experiences. The experiment was explicitly designed to maximize the combined effect of psilocybin and suggestion.

Critique of the Questionnaire

Pahnke designed a questionnaire to measure mystical experiences specifically for the experiment. The questionnaire includes eight categories, including sense of unity, transcendence of time and space, sense of sacredness, sense of objective reality, deeply felt positive mood, ineffability, paradoxicality and transiency.

Zaehner’s critique of Pahnke’s questionnaire was that it did not contain a category for experiences which are specifically Christian. Pahnke asserted that he was simply investigating mystical experiences, regardless of whether or not they were considered religious.

The questionnaire used in the Good Friday experiment has been modified and expanded over the years by Pahnke, William Richards, Stanislav Grof, Franco Di Leo, and Richard Yensen for use in subsequent psychedelic research. The basic items relating to the mystical experience have remained essentially unchanged.

Pahnke’s subjects rated each category on a scale from zero to four, with four indicating that they experienced the category as strong as ever before.

The questions themselves are of two types. The predominant type asks the subject about experiences of a new perspective, and the specific questions determine the completeness with which each subject experienced each category.

The second type of question asks about the loss of a normal state, such as the sense of self. This type of question is a minor weak point of the questionnaire because it can be rated highly without having anything to do with mystical experiences.

The follow-up questionnaire sought to assess the effects of the experience on the subjects’ attitudes and behaviors, including changes in their relationships with others, quiet meditation or devotional life, and their perception of their behavior.

Pahnke’s questionnaire gathered information from the subjects’ self-reports, but did not include information about the internal psychodynamic mechanisms at work within each subject.

In contemporary psychotherapy research, more sophisticated methods than Pahnke’s are used to assess personality change. The results of the follow-up questionnaires are valuable as far as they go, but the long-term follow-up interviews yield more detailed information about the experiences and the persisting effects.


Pahnke determined that a mystical experience must be at least 60 to 70 percent complete for it to be considered complete. Eight out of ten psilocybin subjects experienced at least seven out of nine categories, whereas none of the control subjects had a score higher than this.

When asked at a conference if any of the controls had a mystical experience, Pahnke replied,

One control subject scored high on sacredness and sense of peace, but said his past experiences were much more meaningful.

Pahnke’s six-month follow-up data and the author’s long-term follow-up questionnaire data are displayed in Table 1. The average scores for the control group are overstated somewhat because three out of ten original psilocybin subjects did not complete the long-term follow-up.

The average scores for the eight categories of the mystical experience have changed little over time, and the experimental group has higher scores in every category than the control group.

The experimental group scored higher than the control group in all mystical categories at both the six-month and long-term follow-ups.

The control group scored the highest in sacredness, deeply felt positive mood and sense of objectivity and reality at the six-month follow-up, while all other categories remained virtually the same.

The experimental group reported high levels of persisting positive changes, while the control group reported virtually no persisting positive changes. There was a very low incidence of persisting negative changes in attitudes or behavior in either group.

Psilocybin, when taken by people who are religiously inclined, can facilitate experiences of varying degrees of depth that are identical with or indistinguishable from those reported in the cross-cultural mystical literature.


All subjects contacted a quarter century after the original experiment are currently working and self-supporting. Five out of eight psilocybin subjects and five out of ten placebo subjects are currently working as ministers.

The experimental psilocybin subjects described their Good Friday experience as having had elements of a genuinely mystical nature, while the control subjects could barely remember even a few details of the service.

Most of the psilocybin subjects had subsequent experiences of a mystical nature with which they were able to compare and contrast their psilocybin experience. The drug experiences were reportedly more intense and composed of a wider emotional range than the non-drug experiences.

I can think of no experiences like the Good Friday experience, where I saw the face of Christ, and said, “Let me live and I’ll serve you,” and I’m alive and I’ve served. The prayer state in seventh grade was very similar, too.

Each subject felt that the experience had significantly affected his life in a positive way, and expressed appreciation for having participated in the experiment. The effects included enhanced appreciation of life and of nature, and greater solidarity with foreign peoples.

I participated in an experiment that left me with a completely unquestionable certainty that there is an environment bigger than the one I’m conscious of. I have gotten help with problems and at times I think direction and guidance in problem solving.

Several subjects reported similar effects to the self-reports, and the observations of fellow subjects confirmed the claims of beneficial effects.

Psilocybin subjects reported feeling compassion for minorities, women and the environment, and taking more risks as a result of their Good Friday experience.

When you get a clear vision of death and have experienced it, you don’t fear marching in the Civil Rights Movement or against the Vietnam War.

Subject S.J. found that his Good Friday experience of unity supported his efforts in the political field.

One control subject felt that his experience of the Good Friday service resulted in beneficial personal growth, while another placebo subject had a subsequent psychedelic experience.

Something extraordinary had taken place which had never taken place before. I felt drawn out into infinity, and I lost touch with my mind, and I got the impression that people would continue to live in heaven even after they died.

I was on the floor underneath the chapel pew and was hearing my uncle who had died saying, “I want you to die, I want you to die, I want you to die”. The more I died, the more I appropriated this sense of eternal life.

After receiving the capsule, I started to have a very strong paranoid experience. I got up and left the chapel, and when I went back, I felt like I was in prison because of the bars on the windows.

The inner awareness and feelings I had during the drug experience were similar to a classical mystical experience, and I wanted to get to the bottom of it.

I closed my eyes and the visuals were back, the color patterns were back, and I was in an ocean of bands, streams of color, streaming past me. I could swim down any one of those colors, but I couldn’t decide which one to go out on.

After the psilocybin experience, I never had to consciously make the choice as to what I was going to do career-wise. It was made and I did it afterwards.

Reverend K.B. describes his mystical experience in the following manner:

I closed my eyes and felt a sudden bolt of light, almost like a shock, and a tingling like taking hold of a wire or something. I haven’t found any words to describe it.

I closed my eyes and thought about the procession to the cross. I had an unusually vivid scene of the procession going by, and a sense of being an infant or being born, and a sense of death, too.

I really am glad I took the test, and glad that I was a subject. I don’t think it would be a particularly memorable experience if I had just listened to the service.

I was kneeling there praying and began to feel like I was experiencing the kind of prayer life that I experienced back when I was in the seventh grade, eleven or twelve years old. I discovered that you never quite get to the root of all being in either prayer, or the psilocybin experience.

I had a feeling of being lifted out of my present state, and I stopped worrying about time and all that kind of stuff. I didn’t think Christ or other religious images came into it, and I didn’t think it was a religious experience.

I laid on the front pew and watched myself become nothing and felt that this would never stop. It was one of the most beautiful experiences in my entire life.


The experience was rather removed from the religious context, and there was no talk about mysticism or religious symbols. The energy was almost a sexual thing, an intensity and a joy, and you didn’t sense a difference between the music and the physical objects.

I think that you can have a religious experience without religious symbols, but they can also be divisive.

Two control subjects wanted to have their own psychedelic experience, but several other control subjects decided they had no desire to try psychedelics. They were scared by the behavior of some of their fellow subjects who received psilocybin.

A Significant Omission

Seven psilocybin subjects were formally interviewed, and only two reported completely positive Good Friday experiences. The others all felt moments in which they feared they were either going crazy, dying, or were too weak for the ordeal.

I found unique that what I read was all on the positive up side. I had a down side, though, where I was really just guilty.

Pahnke does mention that two subjects had trouble readjusting to the “ordinary world” after receiving psilocybin, probably including L.R., who refused to participate in the follow-up study.

Pahnke did not report that one subject was given a shot of thorazine as a tranquilizer during the course of the experiment. Several of the subjects and group leaders remembered this incident and reported it in long-term follow-up interviews.

Pahnke probably did not report his use of the tranquilizer because he was afraid that negative aspects of the experiment would be taken out of context and exaggerated. Zaehner’s misreading of Pahnke’s article is an indication of how bias can overwhelm facts.

The subject who was tranquilized was reported to have been deeply moved by a sermon delivered by a very dynamic preacher. The subject went outside of the chapel possibly intending to follow the exhortation.

The group leaders tried to bring Pahnke back inside, but he seemed fearful and was not settling down. Pahnke was tranquilized with thorazine and participated in all further aspects of the experiment.


The original Good Friday experiment, in which psilocybin was used to induce mystical experiences, supports the hypothesis that psychedelic drugs can help facilitate mystical experiences when used by religiously inclined people in a religious setting.

This long-term follow-up provides further support to the findings of the original experiment, which showed that psilocybin users continued to value their psychedelic experiences. The results cast doubt on the assertion that psychedelic users are inferior to non-users in both their immediate content and long-term positive effects.

The long-term follow-up of the psilocybin subjects uncovered data that should have been reported in the original thesis. Pahnke failed to report the administration of the tranquilizer thorazine to one of the subjects who received psilocybin.

Some of the backlash against psychedelics can be traced to the thousands of people who took psychedelics in non-research settings, were unprepared for the frightening aspects of their psychedelic experiences and ended up in hospital emergency rooms.

The widespread use of psychedelics in medical and non-medical settings began in the 1960s and is still taking place, apparently largely underground. Despite the difficult moments several psilocybin subjects passed through, the subjects who participated in the long-term an important incompleteness follow-up reported a substantial amount of persisting positive effects and no significant long-term negative effects.

The lack of long-term negative effects or dysfunction is not surprising, as Strassman’s literature review found that panic reactions and adverse reactions were extremely rare. Additional studies are justified, even in light of the new data about the difficulties of the psychedelic experiences of many of the subjects.

Psychedelic drugs can be used to enhance the psychotherapeutic process, but cultural conditions and obstacles must be considered. D’AQUILI, E., D’AQUILI, B., BAKALAR, J., DEIKMAN, A., DOBKIN DE Rios, M. (1972), Visionary vine: Hallucinogenic healing in the Peruvian Amazon.

The neurophysiological basis for “God” experiences was investigated in 1966 by a pilot project investigating the pharmacological effects of psilocybin in normal volunteers. This study is discussed in the book “Psychedelic Reflections” by GRINSPOON, L. & BAKALAR, J. Several authors have written about the religious implications of psychedelics, including PRINCE, SALMAN, DASS, SCHMTTZ-MOORMAN, SHULGIN, A., SHULGIN, L. A. & JACOB III, P. (1986), SMITH, D. (Ed.) and STAFFORD, P. (1983).

Study details

Compounds studied

Topics studied
Equity and Ethics

Study characteristics
Longitudinal Follow-up Survey Interviews



Authors associated with this publication with profiles on Blossom

Rick Doblin
Rick Doblin Ph.D. is the founder of MAPS. His persistent work since 1986 has been one of the main drivers behind why psychedelics (including MDMA) are now coming back to therapy.

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