Robitussin-AC is not an over-the-counter medication; it is available only by prescription. Robitussin-AC is also known by its generic name, which is codeine and quaifenesin, according to Drugs.com.
The codeine in Robitussin-AC is a narcotic and is added as a cough suppressant that helps control the cough reflex. Guaifenesin is a cough expectorant that eases symptoms of cough and chest congestion by loosening up the mucus in the throat and chest. When combined, these two ingredients can be effective in treating incidences of cough caused by the common cold or upper respiratory infections. Coughs caused by emphysema, asthma or smoking cannot be effectively treated with Robitussin-AC, according to Drugs.com.