Treat the cause. A simple vrial infection/cold may last a few days; a wk or so for viral bronchitis and flu (cough may last 3 wks). Cough suppressant, fluid, and rest often do the trick. The so called 'walking penumonia' and pertussis may linger for wks to months if not properly treated. Smokers/cystic fibrosis people may have chronic bronchitis. Consult doc for eval if symptoms lasting too long. Good luck.