Background: Recent research indicates that psychedelic-assisted therapy (PAT) may be a safe and effective treatment for several psychiatric disorders, including those experienced by people with serious physical illness. Understanding health care workers' (HCWs') attitudes and knowledge about the clinical application of psychedelics for patients with serious illness is important in progressing research and identifying factors to consider in potential future implementation of PAT. Aim: The aim of this systematic review was to synthesize quantitative, qualitative, and mixed methods studies that explored HCWs' attitudes and knowledge about the role of psychedelics in treating psychological distress in patients with serious illness. Design: MEDLINE, PsycInfo, and CINAHL were searched for quantitative, qualitative, or mixed methods primary empirical studies, published in English from 2006 onward. Two reviewers independently screened articles for inclusion. The Joanna Briggs Institute (JBI) convergent approach to mixed methods systematic reviews guided synthesis of the findings of included studies. One reviewer extracted data from included studies which was checked for accuracy by another reviewer. Two reviewers independently critically appraised included studies using JBI critical appraisal tools. Results: The review included nine studies (seven qualitative, two quantitative) conducted in four countries. Five themes were developed: Polarized views about PAT for patients with serious illness; attitudes often informed by PAT research knowledge and heuristic methods; stronger evidence base needed to increase HCWs' confidence and support implementation of PAT; barriers may hinder PAT's potential integration into existing care models; and team-based approach and clinical education are essential to facilitate PAT. Conclusion: Although support for PAT varied, most HCWs perceived potential benefits in treating refractory distress, desired education about PAT, and called for further research to develop a stronger evidence base. Limitations of the review and included studies are discussed, along with implications of the findings and recommendations for future research.