['refractory chronic cough']
['gefapixant', 'placebo (for gefapixant)']

        Inclusion Criteria:

          -  Women and Men between 18 and 80 years of age inclusive

          -  Have refractory chronic cough

          -  Women of child-bearing potential must use 2 forms of acceptable birth control - Have
             provided written informed consent.

          -  Are willing and able to comply with all aspects of the protocol

        Exclusion Criteria:

          -  Current smoker

          -  Forced Expiratory Volume in 1 second (FEV1)/Forced Vital Capacity (FVC) ratio <60%

          -  History of upper or lower respiratory tract infection or recent significant change in
             pulmonary status within 4 weeks of the Baseline Visit

          -  History of opioid use within 1 week of the Baseline Visit

          -  Body mass index (BMI) <18 kg/m^2 or ≥ 40 kg/m^2

          -  History of concurrent malignancy or recurrence of malignancy within 2 years prior to
             Screening (not including subjects with <3 excised basal cell carcinomas)

          -  Screening systolic blood pressure (SBP) >160 mm Hg or a diastolic blood pressure (DBP)
             >90 mm Hg

          -  Clinically significant abnormal electrocardiogram (ECG) at Screening

          -  Significantly abnormal laboratory tests at Screening

          -  Pregnant or Breastfeeding

          -  Other severe, acute, or chronic medical or psychiatric condition or laboratory
             abnormality that may increase the risk associated with trial participation or
             investigational product administration or may interfere with the interpretation of
             trial results and, in the judgment of the Investigator or Sponsor, would make the
             participant inappropriate for entry into this trial
      