Background: Various studies have explored potential therapeutic applications of capsaicin in human medicine, for example in pain, obesity, cancer, cardiovascular and respiratory disease. The aim of this scoping review was to identify and chart available evidence on therapeutic applications of capsaicin in humans using any mode of capsaicin delivery to treat conditions of the respiratory system. Methods: Electronic bibliographic databases (Web of Science, PubMed, Medline, ScienceDirect, Embase, Scopus) were searched from inception to 2021 to identify experimental studies reporting clinical outcomes of therapeutic applications of capsaicin. Studies with or without control group published in peer-reviewed journals were included. Animal studies, studies of human cell lines, and physiological proof of concept studies were excluded. Reviewer pairs independently double-screened 2799 search results for inclusion. Results: Twenty-three original studies were included. Capsaicin has been investigated for the treatment of non-allergic rhinitis (n = 15), nasal polyposis (n = 3), allergic rhinitis (n = 2), unexplained chronic cough (n = 2), and prevention of aspiration pneumonia (n = 1). Modes of delivery included intranasal application (nasal spray, soaked pads, solution), inhalation, ingestion, and aural ointment. Seventeen studies reported positive effects of capsaicin on clinical outcomes for rhinitis, nasal polyposis, chronic cough, and pneumonia. Sixteen studies reported on the safety of capsaicin, with no reports of significant adverse events and overall fair to good patient acceptability. Conclusion: While the evidence identified in this review has limited implications for clinical practice, studies support the general safety of capsaicin as administered in these studies and highlight emerging strands of research and clinical hypotheses which warrant further examination.
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