Refractory Chronic Cough Improvement Via NAL ER (RIVER)

Key Inclusion Criteria: * Diagnosis of refractory chronic cough (RCC) for at least one year * Chest radiograph or CT of thorax within 24 months or during screening not demonstrating any significant abnormalities contributing to RCC Exclusion Criteria: * Diagnosis of sleep apnea * Respiratory tract infection within 6 weeks of Baseline * History of bronchiectasis, COPD, or IPF * History of uncontrolled asthma * Current smokers/vapers, quit smoking with \<=12 months, using nicotine supplements, or history of \>=20 pack years * History of major psychiatric disorder * History of substance abuse * Pregnant or lactating females * Known intolerance to opioids * Abnormal kidney or liver functions based on Screening lab results. * Known hypersensitivity to nalbuphine or to NAL ER excipients * Previous participation in a nalbuphine ER clinical study * Use of opiates, benzodiazepines, or MAOIs within 14 days of Baseline * Use of pregabalin, gabapentin, thalidomide for treatment of cough within 14 days of Baseline * Use of ACE inhibitors within 12 weeks of Baseline * Use of a medication having a "known risk" of Torsade de Pointes (categorized as "KR" on the Credible Meds® website.) 4 weeks prior to Baseline * Use of unstable doses of medications associated with a potential risk of QT prolongation but not clearly associated with Torsade de Pointes within 4 weeks of screening. * Use of unstable doses of cough suppressants within 14 days of Baseline * Use of unstable doses of medications that affect serotonergic neurotransmission that may cause serotonin syndrome with opioids within14 days of Baseline * Use of unstable doses of P450 isozyme inhibitors/inducers within 14 days of Baseline Other protocol defined inclusion/exclusion criteria may apply.