There are many brands and forms of guaifenesin and pseudoephedrine available and not all brands are listed on this leaflet. Guaifenesin is an expectorant. It helps loosen congestion in your chest and throat, making it easier to cough out through your mouth. Pseudoephedrine is a decongestant that shrinks blood vessels in the nasal passages. Dilated blood vessels can cause nasal congestion (stuffy nose). Guaifenesin and pseudoephedrine is a combination medicine used to treat stuffy nose and sinus congestion, and to reduce chest congestion caused by the common cold or flu. Guaifenesin and pseudoephedrine may also be used for purposes not listed in this medication guide.