Mucinex DM is a 12 hour extended release medicine that controls cough and loosens mucus. Mucinex DM contains an expectorant and a cough suppressant. Active ingredients: 1200 mg guaifenesin 60 mg dextromethorphan HBr Maximum Strength Mucinex DM: Helps loosen phlegm Temporarily relieves cough due to throat or bronchial irriation Temporarily relieves the intensity of coughing Temporarily relieves the impulse to cough to help you get to sleep. 14 extended release bi-layer tablets.