A Randomized, Double-Blind, Placebo-Controlled Single-Ascending-Dose Study to Identify a Subperceptual Dose of Psilocybin in Healthy Adults

This Phase 1 randomized, double-blind, placebo-controlled study tested single oral psilocybin doses of 0.5–4.0 mg in 56 healthy adults. There were no serious adverse events or cognitive decrements. Subjective effects became distinguishable from placebo at 2.5 mg and above, while altered-state scores remained low; dose-related pupil dilation confirmed pharmacological activity. The study did not test treatment efficacy or repeated outpatient dosing.