This thesis explores the re-emergence of psilocybin as a promising treatment for depression. It examines psilocybin’s historical use, pharmacological action on 5-HT₂A receptors, and its effects on neuroplasticity and cognition. Key clinical trials are reviewed, highlighting rapid and sustained therapeutic benefits in controlled settings, along with safety considerations and ethical implications. The study concludes that psilocybin, with proper safeguards, could represent a transformative approach in psychiatric care, warranting further large-scale research.