Pahnke’s “Good Friday Experiment”: A Long-Term Follow-Up and Methodological Critique

Findings of the Original Study and Long-Term Follow-Up

Pahnke arbitrarily determined that for a mystical experience to be considered complete for the purposes of the experiment, out of the maximum total possible score, “the total score and the score in each separate category must be at least 60 to 70 percent” (Pahnke, 1967, p. 66). According to this cut-off point, “Four of the ten psilocybin subjects reached the 60 to 70 percent level of completeness, whereas none of the controls did” (Pahnke, 1967, p. 64). Looked at by subjects and categories, Pahnke reported that “eight out of ten of the experimental subjects experienced at least seven out of the nine categories. None of the control group, when each individual was compared to his matched partner, had a score which was higher” (Pahnke, 1966, p. 647). In every general category and in every specific question, the average score of the experimental subjects exceeded that of the control subjects. The differences between the groups in the scores on the questionnaires were significant at p<.05 level for all categories.

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

To take an individual case, there was one control subject who scored fairly high on sacredness and sense of peace and that he himself, in his written account, said “It was a very meaningful experience, but in the past I’ve certainly had one that was much more so” (Pahnke, 1966, p. 648).

Pahnke’s six-month follow-up data and the author’s long-term follow-up questionnaire data, both of which used the same instrument, are displayed in Table 1. The six-month scores are listed first and the long-term follow-up scores follow in parentheses. For each category, the percentages in the chart represent the total scores of the subjects divided by the highest possible scores that could have been reported. The numbers measure the completeness with which each category was experienced.

Comparisons can reliably be made between the control group’s six-month and long-term scores because nine out of the original ten control group subjects participated in the long-term follow-up and the variance in scores between control subjects was small. The absence of completed long-term questionnaires from three of the ten original subjects from the psilocybin group makes comparing their six-month and long-term scores more difficult. The long-term follow-up interviews produced specific information suggesting that one of the three missing psilocybin subjects had scores significantly lower than average. No information was generated suggesting that the other two missing subjects had scores significantly different than average. The average scores for the long-term follow-up may thus overstate somewhat the scores from the entire psilocybin group.

The average scores for the eight categories of the mystical experience and the scores for persisting positive and negative changes in attitude and behavior have changed remarkably little for either the controls or the experimentals despite the passage of between twenty-four and twenty-seven years between the two tests. The questionnaire seems to be reliable and indicates that time has not substantially altered the opinions of the subjects about their experiences. In the long-term follow-up even more than in the six-month follow-up, the experimental group has higher scores than the control group in every category. For the long-term follow-up, these differences are significant at p<.05 in every category.

“Good Friday Experiment” Experimental and Control Groups at Six-Month and Long-Term Follow-Up, Shown as Percentages of Maximum Possible Scores

Category	Experimentals Six-Month	Experimentals Long-Term	Controls Six-Month	Controls Long-Term
1. Unity A. Internal	60	77	5	5
B. External	39	51	1	6
2. Transcendence of Time and Space	78	73	7	9
3. Deeply Felt Positive Mood	54	56	23	21
4. Sacredness	58	68	25	29
5. Objectivity and Reality	71	82	18	24
6. Paradoxicality	34	48	3	4
7. Alleged Ineffability	77	71	15	3
8. Transiency	76	75	9	9
Average	60.8	66.8	11.8	12.2
9. Persisting Positive Changes	48	50	15	15
10. Persisting Negative Changes	6	6	2	4

Note: At Six-Month Follow-Up, Exper. N=10, Control N=10. At Long-Term Follow-Up, Exper. N=7, Control N=9. p<.05 for all category comparisons at both six-month and long-term.

For the experimental group, the average score for the mystical categories at the six-month follow-up was 60.8 percent. They scored 66.8 percent at the long-term follow-up. In the six-month follow-up, the experimental group scored above 34 percent in all categories while in the long-term follow-up they scored above 48 percent in all categories. The experimental group scored the highest in those categories that typify a different state of consciousness such as transcendence of time and space, alleged ineffability and transiency.

For the control group, the average score for the eight categories of mystical experience at the six-month follow-up was 11.8 percent. They scored 12.2 percent at the long-term follow-up. The highest score of the control group at either time was 29 percent, in the sacredness category. The control group scored the highest in the categories of experience that religious services are most likely to induce, namely sense of sacredness, deeply felt positive mood and sense of objectivity and reality.

For the psilocybin group, the long-term follow-up yielded moderately increased scores in the categories of internal and external unity, sacredness, objectivity and reality, and paradoxicality, while all other categories remained virtually the same as the six-month data. Several decades seem to have strengthened the experimental groups’ characterization of their original Good Friday experience as having had genuinely mystical elements. For the controls, the only score that changed substantially was that of alleged ineffability, which decreased.

A relatively high degree of persisting positive changes was reported by the experimental group while virtually no persisting positive changes were reported by the control group. In the open-ended portion of the long-term follow-up questionnaire, experimental subjects wrote that the experience helped them to resolve career decisions, recognize the arbitrariness of ego boundaries, increase their depth of faith, increase their appreciation of eternal life, deepen their sense of the meaning of Christ, and heighten their sense of joy and beauty. No positive persisting changes were reported by the control group in the open-ended section of the follow-up questionnaire.

There was a very low incidence of persisting negative changes in attitudes or behavior in either group at either the six-month follow-up or the long-term follow-up. However, the one psilocybin subject reported to have had the most difficult time during the experiment was the one who declined this author’s request to be interviewed in person or fill out a questionnaire, placing in question the generalizability of this finding for the long-term.

Both the six-month and long-term follow-up questionnaire results support Pahnke’s hypothesis that psilocybin, when taken in a religious setting by people who are religiously inclined, can facilitate experiences of varying degrees of depth that either are identical with, or indistinguishable from, those reported in the cross-cultural mystical literature. In addition, both the six-month and the long-term follow-up questionnaire results support Pahnke’s hypothesis that the subjects who received psilocybin, more so than the controls, experienced substantial positive persisting effects in attitude and behavior.