The therapeutic alliance between study participants and intervention facilitators is associated with acute effects and clinical outcomes in a psilocybin-assisted therapy trial for major depressive disorder.

We examined if the therapeutic alliance between study participants and intervention facilitators in a psilocybin-assisted therapy (PAT) trial changed over time and whether there were relationships between alliance, acute psilocybin experiences, and depression outcomes. In a randomized, waiting list-controlled clinical trial for major depressive disorder in adults (N = 24), participants were randomized to an immediate (N = 13) or delayed (N = 11) condition with two oral doses of psilocybin (20mg/70kg and 30mg/70kg). Ratings of therapeutic alliance significantly increased from the final preparation session to one-week post-intervention (p = .03, d = .43). A stronger total alliance at the final preparation session predicted depression scores at 4 weeks (r = -.65, p = .002), 6 months (r = -.47, p = .036), and 12 months (r = -.54, p = .014) post-intervention. A stronger total alliance in the final preparation session was correlated with higher peak ratings of mystical experiences (r = .49, p = .027) and psychological insight (r = .52, p = .040), and peak ratings of mystical experience and psychological insight were correlated with depression scores at 4 weeks (r = -.45, p = .030 for mystical; r = -.75, p < .001 for insight). Stronger total alliance one week after the final psilocybin session predicted depression scores at 4 weeks (r = -.85, p < .001), 3 months (r = -.52, p = .010), 6 months (r = -.77, p < .001), and 12 months (r = -.61, p = .001) post-intervention. These findings highlight the importance of the therapeutic relationship in PAT. Future research should explore therapist and participant characteristics which maximize the therapeutic alliance and evaluate its relationship to treatment outcomes. Trial registration: Registration: Clinicaltrials.gov NCT03181529. https://classic.clinicaltrials.gov/ct2/show/NCT03181529.

Study protocol of an open-label proof-of-concept trial examining the safety and clinical efficacy of psilocybin-assisted therapy for veterans with PTSD.

INTRODUCTION: Psilocybin-assisted therapy has shown significant promise in treating the cluster of mood and anxiety symptoms that comprise post-traumatic stress disorder (PTSD) but has yet to be tested specifically in this condition. Furthermore, current pharmacological and psychotherapeutic treatments for PTSD are difficult to tolerate and limited in efficacy, especially in the US Military Veteran (USMV) population. This open-label pilot study will examine the safety and efficacy of two psilocybin administration sessions (15 mg and 25 mg), combined with psychotherapy, among USMVs with severe, treatment resistant PTSD. METHODS AND ANALYSIS: We will recruit 15 USMVs with severe, treatment resistant PTSD. Participants will receive one low dose (15 mg) and one moderate/high dose (25 mg) of psilocybin in conjunction with preparatory and post-psilocybin therapy sessions. The primary safety outcome will be the type, severity and frequency of adverse events and suicidal ideation/behaviour, as measured by the Columbia Suicide Severity Rating Scale. The primary outcome measure for PTSD will be the Clinician Administered PTSD Scale-5. The primary endpoint will be 1 month following the second psilocybin administration session, and the total follow-up time will be 6 months. ETHICS AND DISSEMINATION: All participants will be required to provide written informed consent. The trial has been authorised by the Ohio State University Institutional Review Board (study number: 2022H0280). Dissemination of results will occur via a peer-reviewed publication and other relevant media. TRIAL REGISTRATION NUMBER: NCT05554094.