Delsym Cough + Chest Congestion DM liquid relieves cough, plus thins and loosens mucus that causes your chest congestion. It helps thin and loosen mucus and thin bronchial secretions to rid the bronchial passageways of bothersome mucus and make coughs more productive. Temporarily relieves cough due to minor throat and bronchial irritation as may occur with the common cold or inhaled irritants the intensity of coughing the impulse to cough to help you get to sleep.