Long-term outcomes of single-dose psilocybin for U.S. military Veterans with severe treatment-resistant depression - 12-month data from an open-label pilot study

Background: One-third of Veterans with major depressive disorder suffer from treatment-resistant depression (TRD). This is the first study to evaluate the long-term outcomes of psilocybin in Veterans with severe TRD.Methods: This paper presents 12-month results from an open-label pilot study assessing the effects of 25 mg psilocybin in Veterans with severe TRD, defined as a major depressive episode failing to respond to ≥5 treatments, or lasting >2 years. 10 out of 15 participants completed the 12-month follow-up. Depression severity was measured by Montgomery-Åsberg Depression Rating scale (MADRS) at 6, 9, and 12 months posttreatment. Response was defined as ≥50 % reduction in MADRS, and remission as ≤10 MADRS score.Results: Depression scores show significant reductions from baseline across all timepoints. However, there was an increase in MADRS scores from short-term timepoints (Weeks 3 and 12) to Month 12. Of 10 participants, at Month 6, 80 % met response and 50 % met remission criteria for the MADRS. At Month 9, acute responses began to wane. At Month 12, 40 % maintained response and 30 % maintained remission.Limitations: Limitations include the small sample size and its uncontrolled, unblinded design.Conclusions: In this first-of-kind study on long-term effects of psilocybin for Veterans with severe TRD, depression scores showed significant sustained reductions up to 12-months. However, the antidepressant effects began to wane at 6 months, and then more substantially after 9 months, although these increases in MADRS did not reach statistical significance. Further research is needed.