Trajectories of psychedelic-assisted change: An observational study of a psilocybin retreat program followed by psychotherapeutic interventions

Abstract Despite growing interest in psychedelic-assisted psychotherapy, research investigating the psychotherapeutic components is lacking. This leaves unanswered questions regarding the psychotherapy's necessity and form. This observational study addresses this gap by measuring the outcomes of a psilocybin truffle retreat, followed by the outcomes of two psychotherapy interventions that targeted psychological content from the retreat ( n = 50). Participants attended an Acceptance and Commitment Therapy (ACT)-informed psilocybin retreat program followed by psychotherapy. Mid-data collection the psychotherapy intervention was revised: ACT-SPT ( n = 23; self-perspective taking and cognitive defusion) was altered to ACT-PMNR ( n = 27; Psychedelic Memory Network Reexperiencing). Both approaches aimed to support long-term psychological change. Participants completed measures of Depression, Anxiety, Stress (DASS-21), Valued Living (VLQ), and measures of Psychological Flexibility, Mindfulness, Cognitive Fusion, Well-being and Life Functioning at four time points: baseline, post-psilocybin, post-psychotherapy and follow-up. For the combined effect of retreat and subsequent interventions, a Linear Mixed Model (LMM) analysis found significant changes in all measures. Comparing psychotherapy trajectories, there was a significant Time × Intervention interaction for DASS-21 (Anxiety), CORE-5 (Well-being, Life Functioning). During the post-psilocybin period, ACT-SPT trajectories drifted towards baseline levels, whilst ACT-PMNR continued to improve. Long-term LMM follow-up of ACT-PMNR trajectories showed significant change across all measures. Penalized spline growth curves showed that post-therapy change exceeded baseline-to-post-retreat change. At follow-up these trajectories often sustained or further improved. Conclusions Targeted post-psilocybin interventions may further build on the initial psilocybin retreat result. These interventions may drive measurable changes in the specific domains they engage. Randomized studies are warranted to confirm these findings.