Background/Objectives: Psilocybin-assisted therapy has progressed from early proof-of-concept work to a substantially expanded evidence base, with four pivotal studies published in 2025-2026 that were not incorporated into earlier reviews. This review synthesizes the pharmacological and neurobiological foundations of psilocybin and appraises clinical evidence across major depressive disorder (MDD), treatment-resistant depression (TRD), post-traumatic stress disorder (PTSD), cancer-related distress, and substance use disorders, emphasizing long-term durability, expanding indications, and methodological limitations. Methods: A narrative review was conducted using a targeted search of PubMed/MEDLINE, Embase, Scopus, and Web of Science (January 2000-April 2026), emphasizing 2025-2026 publications. Predefined eligibility principles prioritized randomized controlled trials, long-term follow-up studies, and systematic reviews; formal PRISMA procedures were not applied, consistent with the narrative design. Results: Four 2025-2026 studies extend the evidence base: a 52-week follow-up confirming dose-dependent maintenance of antidepressant benefit after a single 25 mg psilocybin session; the first pilot study in Veterans with severe TRD, reporting a 60% response rate at three weeks; the first safety trial in PTSD, where symptom improvement tracked self-transcendent experience intensity but worsened with session anxiety; and a living review of 15 randomized trials confirming a meaningful antidepressant effect while identifying functional unblinding as a substantial threat to effect estimates. Conclusions: Evidence supports psilocybin-assisted therapy as mechanistically distinct and clinically promising, most strongly in MDD and TRD, with preliminary support in PTSD and Veterans. Functional unblinding, small open-label designs, narrow safety populations, and absent SSRI-integration protocols constrain the current conclusions.
Psychedelic Science