Hydrocodone is a narcotic cough suppressant (antitussive). It works on a certain part of the brain to reduce the urge to cough. Chlorpheniramine (CPM) is an antihistamine that helps relieve symptoms such as watery eyes; itchy eyes, nose, throat; runny nose; and sneezing. Pseudoephed is a decongestant that relieves nasal congestion by shrinking the blood vessels in the nasal passages. Guaifenesin is an expectorant that helps loosen congestion in the chest and throat. It works by making it easier to cough out through your mouth.