Rationale Although psilocybin has been used for centuries
for religious purposes, little is known scientifically about its
acute and persisting effects.
Objectives This double-blind study evaluated the acute and
longer-term psychological effects of a high dose of psilocybin
relative to a comparison compound administered under
comfortable, supportive conditions.
Materials and methods The participants were hallucinogennaïve
adults reporting regular participation in religious or
spiritual activities. Two or three sessions were conducted at
2-month intervals. Thirty volunteers received orally administered
psilocybin (30 mg/70 kg) and methylphenidate
hydrochloride (40 mg/70 kg) in counterbalanced order. To
obscure the study design, six additional volunteers received
methylphenidate in the first two sessions and unblinded
psilocybin in a third session. The 8-h sessions were conducted
individually. Volunteers were encouraged to close
their eyes and direct their attention inward. Study monitors
rated volunteers’ behavior during sessions. Volunteers
completed questionnaires assessing drug effects and mystical
experience immediately after and 2 months after
sessions. Community observers rated changes in the
volunteer’s attitudes and behavior.
Results Psilocybin produced a range of acute perceptual
changes, subjective experiences, and labile moods including
anxiety. Psilocybin also increased measures of mystical
experience. At 2 months, the volunteers rated the psilocybin
experience as having substantial personal meaning and
spiritual significance and attributed to the experience sustained
positive changes in attitudes and behavior consistent
with changes rated by community observers.
Conclusions When administered under supportive conditions,
psilocybin occasioned experiences similar to spontaneously
occurring mystical experiences. The ability to
occasion such experiences prospectively will allow rigorous
scientific investigations of their causes and consequences.