Cannabis Use and the Psychological and Psychosocial Outcomes after Psilocybin-Assisted Therapy in Adults with Cancer: A Systematic Review

Mark Moffatt
University of Miami

Co-authors: Mark Moffatt¹, Josue F. Munguia¹, Anthony Alfonso¹, Ciné Brown¹, Amrit Baral^1,2, Winston de la Haye^1,3, Denise C. Vidot^1
1University of Miami, ²Johns Hopkins University, ³University of West Indies - Mona

Background: Psilocybin-assisted therapy (PAT) has emerged as an intervention for psychological and existential distress among adults with cancer, concurrent to cancer serving as a qualifier for medical cannabis. Despite the increased access to both medical cannabis and psilocybin, there is limited clinical research and evidence examining the effects of PAT in cancer patients who may or may not consume cannabis.

Objective: To evaluate the psychological (depression, anxiety, distress, well-being), psychosocial (spiritual, existential functioning, post-traumatic growth), and cannabis use following PAT among cancer survivors.

Methods: PubMed and ClinicalTrials.gov were searched using a specific Boolean search strategy; 732 studies were imported into Covidence for screening; 605 duplicates were removed. A strict eligibility criterion was developed using the PICOS framework, and three independent reviewers conducted a multistage screening. Eligible studies included adults aged >18y with any cancer type or stage who received ≥1 dose of psilocybin with structured therapeutic support before, during, and after treatment, and that reported psychological, psychosocial, or quality-of-life outcomes. Nonhuman studies, non-English publications, incomplete/ongoing studies, reviews, meta-analyses, case reports, and other nonoriginal reports were excluded. Authenticity and methodological rigor was also enhanced by filtering for other systematic reviews on PubMed; 36 were found and evaluated against our specific eligibility criteria. Evidence quality was assessed using the Johns Hopkins Nursing Evidence-Based Practice Rating Scale.

Results: Eight studies conducted in the United States (7) and Canada (1), representing 79 unique participants, met inclusion criteria. Designs included randomized controlled trials, open-label trials, pilot studies, longitudinal follow-up studies, and qualitative investigations. A single psilocybin dose of 0.3 mg/kg or 25 mg, administered with psychotherapy, was associated with rapid and sustained reductions in depression, anxiety, demoralization, and existential distress, alongside improvements in spiritual well-being and quality of life. Long-term follow-up suggested persistent clinical benefit in approximately 60%–80% of participants at 3.2 to 4.5 years within all psychological domains. Findings for death anxiety were mixed and PAT was generally tolerated. Several included studies noted that participants used cannabis and drew comparisons between cannabis and psilocybin. This suggests that familiarity and perception of cannabis may influence acceptability of or engagement with psychedelic-assisted therapy in oncology populations.

Conclusion: Larger, more diverse randomized trials are needed to clarify efficacy, durability, safety, mechanisms, and the independent contributions of cannabis, psilocybin and psychotherapy. These findings highlight an area for future research direction over how prior cannabis use exposure could influence psilocybin-assisted therapy sessions in cancer populations.