Benylin Dry Coughs contains Dextromethorphan which helps to suppress the cough mechanism, and Levomenthol, a decongestant which works to help relieve stuffiness in the nose to make breathing easier. It also contains Diphenhydramine which helps to relieve a runny nose. A dry cough is also known as a non-productive cough because it does not produce any phlegm. Dry coughs are caused by an inflammation of the upper airways due to dust, foreign bodies, or an infection. This product helps to suppress the coughing mechanism and relieve stuffiness.