Psilocybin is rapidly converted to its active metabolite psilocin after oral intake. Psilocin reaches peak concentration in blood plasma between 1.8 and 4 hours, with maximum concentration ranging from 8.2 ng/mL in plasma to 871 ng/mL in urine, depending on dose. Its bioavailability is about 53%, and it distributes extensively into tissues, with volume of distribution between 277 and 1016 liters. Metabolism involves CYP2D6 and CYP3A4 enzymes, plus monoamine oxidase A, producing 4-hydroxyindole-3-acetic acid and 4-hydroxytryptophol. Elimination half-life ranges from 1.5 to 4 hours. These pharmacokinetics vary with dosage, route, and species, and the role of CYP enzymes indicates possible drug interactions.
In a retrospective chart review of 209 adults with treatment-resistant depression treated with intravenous ketamine, depressive and anxiety symptoms improved significantly over four or six infusions, but the improvements were modest and highly variable across individuals. Anxiety symptoms improved more slowly and less robustly than depressive symptoms. End-of-treatment response and remission rates were numerically higher after six infusions than after four, but the difference was not statistically significant. Four distinct patterns of symptom change emerged for both depression and anxiety, highlighting the heterogeneity of treatment response. Durability after six infusions could not be assessed because follow-up data were available only for the four-infusion group.