According to MedicineNet, guaifenesin is the generic name for the brand named medication, Mucinex. Guaifenesin is an expectorant that promotes elimination of mucus from the lungs.
MedicineNet explains that guaifenesin works by thinning the mucus and lubricating the irritated respiratory tract. Guaifenesin is a common ingredient in many different over-the-counter cough and cold medications. Generally, guaifenesin is prescribed to treat coughs as a result of colds or upper respiratory infections. Guaifenesin is recommended for patients 12 years of age and older. Side effects of this medication are typically uncommon; however, nausea, vomiting, headache and rash can occur. There are no known interactions between guaifenesin and other medications.