RecruitingDrug trialPsilocybin Therapy in Advanced CancerThe purpose of this research is to study the safety and effects of single-dose psilocybin 25mg versus an active placebo (single dose niacin 100mg) in the treatment of anxiety, depression, and existential distress (i.e., loss of meaning and hope; fear of death) in advanced cancer (i.e., stage 3 or 4). Study medications will be administered in conjunction with brief psychotherapy that is designed to treat anxiety, depression and existential distress in advanced cancer.