Inclusion Criteria:

• Female and males between 18 and 80 years of age
• Have a diagnosis of treatment refractory chronic cough or unexplained cough for at least one year
• Chest radiograph or computed tomography (CT) Thorax within the last 5 years not demonstrating any abnormality considered to be significantly contributing to the chronic cough
• At Screening have a score of ≥ 40mm on the Cough Severity VAS
• At Baseline (Day 0) have a score of ≥ 40mm on the Cough Severity VAS
• All female subjects who are of childbearing potential must practice highly effective contraception (i.e., pregnancy prevention method with a failure rate of < 1% per year) from the time of the initial screening visit until 4 weeks after last dose of study drug. Please refer to the protocol for acceptable methods of contraception

Exclusion Criteria:

• Prior treatment with serlopitant or other NK1-R antagonist
• Presence of any medical condition or disability that could interfere with study
• History of hypersensitivity to serlopitant or any of its components
• Currently pregnant or male partner of pregnant female
• Females of childbearing potential who are unable or unwilling to use adequate contraception or who are breast feeding
• Current smoker or individuals who have given up smoking within the past 12 months
• FEV1/FVC < 60%
• Body mass index (BMI) <18 kg/m2 or ≥ 40 kg/m2 at Screening
• History of upper or lower respiratory tract infection or recent significant change in pulmonary status within 4 weeks of the Baseline Visit (Day 0)
• History of cystic fibrosis
• History of opioid use within 1 week of the Baseline Visit (Day 0)
• Requiring concomitant therapy with prohibited medications
• Treatment with biologic therapies within 8 weeks or 5 half-lives prior to the Baseline Visit (Day 0), whichever is longer
• Treatment with strong CYP3A4 inhibitors within 4 weeks prior to the Baseline Visit (Day 0)
• Treatment with any investigational therapy within 4 weeks (investigational biologic therapies within 8 weeks) prior to the Baseline Visit (Day 0)
• Serum creatinine, total bilirubin, alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > 2x the upper limit of normal (ULN) during screening
• Positive test for any drug of abuse
• History of malignancy within 5 years prior to the Baseline Visit (Day 0), with the exception of completely treated and non-metastatic basal cell carcinoma or squamous cell carcinoma of the skin
• Any known psychiatric diagnosis meeting DSM-5 criteria which may confound the assessment of serlopitant safety or efficacy, or interfere with the subject's ability to comply with protocol-mandated activities, within 3 years prior to randomization. Examples of such DSM-5 diagnoses include but are not limited to major depressive disorder, bipolar disorder, schizophrenia, psychotic disorder, intellectual disability, severe alcohol use disorder.
• Known active hepatitis infection
• Known history of human immunodeficiency virus (HIV) infection