DEXTROMETHORPHAN HBR. & CHLORPHENIRAMINE MALEATE , Its mechanism of action is to reduce the surface tension and viscosity of the mucus, which increases the ease of expectoration. Respiratory mucus removal is facilitated by increased flow of the thinned secretions via ciliary action. Chlorpheniramine is an antihistamine. Dextromethorphan is a cough suppressant. DEXTROMETHORPHAN HBR. & CHLORPHENIRAMINE MALEATE is a combination medicine used to treat sneezing, runny nose, and cough caused by the common cold. Chlorpheniramine helps control the symptoms of cold or allergies but will not treat the cause of the symptoms or speed recovery. Chlorpheniramine is in a class of medications called antihistamines. It works by blocking the action of histamine, a substance in the body that causes allergic symptoms.