Results From a Long-Term Observational Follow-Up Study of a Single Dose of Psilocybin for a Treatment-Resistant Episode of Major Depressive Disorder

Background: The largest randomized study of psilocybin to date demonstrated the efficacy of COMP360 25 mg (Compass Pathways' investigational proprietary pharmaceutical-grade synthesized psilocybin formulation) in participants with treatment-resistant depression (COMP 001), compared with 10 mg and 1 mg doses. Here, we report findings from COMP 004, a 52-week observational follow-up of patients from COMP 001 and COMP 003, a small open-label study of the coadministration of 25 mg COMP360 with continuing antidepressant treatment. Methods: Adverse events (AEs) were collected over the full 52-week period. The primary efficacy endpoint was time to a prespecified depressive event over the 52 weeks following COMP360 administration in COMP 001 participants, presented as Kaplan-Meier estimates. A post hoc analysis included only participants that entered COMP 004. Data were collected from July 2020 to July 2022. Results: Sixty-six participants entered COMP 004 (COMP 001, n = 58 [25 mg group n = 22, 10 mg group n = 19, 1 mg group n = 17]; COMP 003, n = 8). Few AEs were reported post-entry into COMP 004, with 1 AE of mild suicidal ideation in the 1 mg group deemed possibly related to study drug. For all COMP 001 patients (n = 233), median time to depressive event was greater for the 25 mg group (92 days) compared to the 10 mg (83 days) and 1 mg (62 days) groups, with the majority of participants having had a depressive event by Week 12 (25 mg n = 37/75, 10 mg n = 38/79, 1 mg n = 44/75). The post hoc supplementary analysis of those who enrolled in COMP 004 from COMP 001 exhibited the difference between groups more strikingly (25 mg, 189 days; 10 mg, 43 days; 1 mg, 21 days); however, only 10 participants experienced a depressive event post-COMP 004 enrollment (25 mg n = 6, 10 mg n = 3, 1 mg n = 1) from COMP 001 and none from COMP 003. At COMP 004 entry, the 1 mg group had the highest number of participants on antidepressant medication (n = 10; 10 mg, n = 9; 25 mg, n = 6) and generally initiated treatment earlier. Conclusion: Over 52 weeks, a single administration of 25 mg psilocybin suggested longer maintenance of antidepressant effect than both 1 mg and 10 mg. Larger long-term studies are required to confirm these findings and provide clarity on the longer-term effects of psilocybin. Trial Registration: ClinicalTrials.gov identifier: NCT04519957.