This combination medication is used to temporarily treat coughing and chest congestion symptoms caused by the common cold, flu, or other breathing illnesses (e.g., sinusitis, bronchitis). Guaifenesin is an expectorant that helps thin and loosen mucus in the lungs, making it easier to cough up the mucus. Codeine is a narcotic cough suppressant (antitussive) that affects a certain part of the brain, reducing the urge to cough.
Source: http://www.healthsquare.com/drugs/121937.htm
