Psilocybin and Depression

"In a new study, researchers from the Psychiatric University Hospital of Zurich have shown that even small amounts of psilocybin can weaken the way our brains process negative emotions and provide a positive mood lift" from the article Compound in Magic Mushrooms Could Treat Depression.

The results are similar to a few other studies along these lines.  The dosage was listed as 0.16 mg/kg in the abstract, equivalent to about 2 or so grams of magic mushrooms.