Griffiths · Journal of psychopharmacology (Oxford, England) 2008 · randomized double-blind crossover follow-up study · n=36

Mystical-type experiences occasioned by psilocybin mediate the attribution of personal meaning and spiritual significance 14 months later.

Cited 913 times in the scientific literature.

Level 2 - randomized trial

Follow-up of a randomized, double-blind active-controlled trial.

PubMed 18593735 · doi:10.1177/0269881108094300 · record verified 2026-08-30

What was done

This was a 14-month follow-up of a double-blind trial evaluating the psychological effects of oral psilocybin (30 mg/70 kg) versus an active control (methylphenidate 40 mg/70 kg) across two or three sessions. Participants were 36 hallucinogen-naive adults who reported regular participation in religious or spiritual activities. During sessions, volunteers were instructed to close their eyes and focus inward in a supportive environment. The follow-up examined the persistence of subjective effects and their relationship to data gathered at screening and session days.

What was found

At 14 months post-session, 58% of participants rated the psilocybin experience as among the top five most personally meaningful experiences of their lives, and 67% rated it among the top five most spiritually significant. In addition, 64% reported an increase in well-being or life satisfaction, and 58% met the criteria for a 'complete' mystical experience. Mystical experience scores measured on session day mediated the ratings of personal meaning and spiritual significance at follow-up. Among the administered scales evaluating personality, affect, quality of life, and spirituality across the study, only the scale measuring mystical experience showed a sustained difference relative to baseline screening.

Why it matters

It demonstrates that a single high-dose psilocybin session in a supportive setting can produce enduring attributions of personal meaning and spiritual significance over a year later, mediated by acute mystical-type experiences.

Limits

The sample size was small (n = 36) and restricted to spiritually active, hallucinogen-naive individuals, limiting generalizability. Most standardized psychometric scales for personality, affect, and quality of life showed no significant change from screening at 14 months, and all data relied on subjective self-reports.

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