This is a randomized, double-blind, placebo-controlled, crossover, multicenter study of AX-8 in participants with unexplained or refractory chronic cough designed to evaluate the effectiveness of AX-8 in reducing cough frequency.

Inclusion Criteria:

• Chest radiograph or computed tomography (CT) of the thorax approximately 12 months before screening not demonstrating any abnormality considered to be significantly contributing to the chronic cough
• Have a diagnosis of refractory chronic cough (RCC) or unexplained chronic cough (UCC) for at least one year
• Women of childbearing potential and their male partners must use 2 acceptable methods of contraception
• Male subjects and their female partners of childbearing potential must use 2 acceptable methods of contraception
• Have provided written informed consent

Exclusion Criteria:

• Positive diagnostic nucleic acid test for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
• Current smoker (including e-cigarettes), individuals who have given up smoking within the past 12 months, or individuals with a smoking history of 20 pack-years
• Treatment with an ACE-inhibitor as the potential cause of a subject's cough or requiring treatment with an ACE-inhibitor during the study or within 12 weeks prior to the Baseline Visit
• History of upper or lower respiratory tract infection or recent significant change in pulmonary status within 4 weeks
• History of cystic fibrosis
• Positive test for any drug of abuse
• History of malignancy within 5 years prior to the Baseline Visit
• History of infection or known active infection with human immunodeficiency (HIV), hepatitis B virus (HBV), or hepatitis C virus (HCV)
• History of hypersensitivity or intolerance to AX-8 or other TRPM8 agonists or any of the excipients