This research review examines how psilocybin, a compound from certain mushrooms, may help treat depression by creating changes in both brain function and psychological experience. Within supportive therapeutic settings, psilocybin appears to increase cognitive flexibility, help people better process emotions, and restore a sense of connection to themselves, others, and the world. The antidepressant benefits seem to work through a combination of direct brain changes and psychotherapeutic factors, rather than through pure pharmacological action alone.