Diagnose first... Before a persistent cough can be treated, you first need to know the etiology of the cough. If it is non-productive, possibilities include bronchospasm of any cause, gerd, post-nasal drip or a combination. All of these have different treatments. If the persistent cough is productive of sputum, you may have chronic bronchitis, a form of copd, again a different treatment. See doctor for diagnosis.