Oral Capsaicin as Treatment for Unexplained Chronic Cough and Airway Symptoms

BackgroundUnexplained chronic cough (UCC) is characterized by persistent coughing without evident medical explanation.Research QuestionDoes daily oral administration of natural capsaicin (chili) improve refractory coughing in patients with UCC?Study Design and MethodsForty-six patients (mean age, 60.5 years) with UCC participated in this crossover, randomized double-anonymized study. For 4 weeks, the participants took capsules containing pure capsaicin orally, and after a washout of 2 weeks, took placebo capsules for 4 weeks. A capsaicin inhalation cough test was used to assess the capsaicin inhalation concentration required to reach two coughs and the capsaicin inhalation concentration required to reach five coughs. The number of coughs in a 24-h period and the number of coughs per hour were recorded on four occasions using the Leicester Cough Monitor. Participants completed questionnaires with items on cough, cough-related symptoms, and quality of life.ResultsThe mean values for capsaicin inhalation concentration required to reach two coughs and the capsaicin inhalation concentration required to reach five coughs increased after the capsaicin treatment period as compared with the first visit (baseline; P < .05 and P < .03, respectively), although they did not differ from the placebo recordings. Neither the capsaicin nor the placebo treatment significantly reduced the cough frequency, nor did they differ between the two treatment periods. When dividing the participants into low-cougher (≤ 400 coughs within 24 h) and high-cougher (> 400 coughs within 24 h) groups, the low coughers experienced a significantly better outcome from capsaicin, but not from placebo. The visual analog scale symptom scores improved after capsaicin treatment compared with baseline and placebo treatment in terms of the frequencies of coughing (P < .001), rhinitis (P < .03), and throat irritation (P < .01). The Leicester Cough Questionnaire scores improved after capsaicin treatment compared with baseline and compared with the placebo treatment group for all the domains (P < .01 for the total score).InterpretationIn this study, capsaicin powder taken orally was found to be clinically effective and well tolerated by patients with UCC. The results suggest a future treatment for UCC.Trial RegistryEuropean Union Drug Regulating Authorities Clinical Trials Database; No.: EudraCT 2016-004463-39; URL: https://www.clinicaltrialsregister.euClinicalTrials.gov; No.: NCT04125563; URL: www.clinicaltrials.gov