"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.