Researchers at the Heffter Research Center in Zurich, Switzerland conduct a double-blind, placebo-controlled study to examine the psychological and physiological effects of psilocybin in humans. Volunteers were given psilocybin doses ranging from 0.045-0.315 mg/kg at intervals over at least two weeks. The data showed orderly dose- and time-dependent effects that changed significantly at many doses and timepoints. The effects began about 20-40 minutes after ingestion, peaked at 60-90 minutes, and diminished over the next 60-90 minutes. Even the threshold dose of 0.045 mg/kg was psychoactive for most of the study subjects. Physiological changes included increases in prolactin, thyroid stimulating hormone, adrenocorticotropic hormone, and cortisol starting at the 0.315 mg/kg dose.