Once ingested, most of the psilocybin is converted into psilocin
within the first hour. Most of the psilocin is then excreted within the
first 8 hours...but portions remain in the system for several weeks.
From Stafford's Psychedelics Encyclopedia
"High dose studies of rats suggest that
psilocin taken orally is distributed throughout the body.
Concentrations in tissues appear highest about half an hour after
ingestion, decreasing rapidly over the next three to four hours. The
adrenal glands of the test animals show the highest concentrations
after the first hour, until then the kidneys have more. The small
intestine, skin, bone marrow, lungs, stomach, and salivary glands also
have significant concentrations-- greater, in fact, than those in the
In the high dose study of rats, all but 6
percent of the psilocybin was excreted within twenty-four hours. In
humans, only 80-85% of psilocybin and its metabolites are excreted
within 8 hours, in the urine (about 65%), bile and feces (15-20%). Some
15-20% lingers on, stored in fatty tissues; significant quantities
appear in urine up to a week later. A full 25% of the originally
administered dose enters urine as psilocin."