We are offering dextromethorphan (dxm) is a synthetic substance most commonly found in a variety of over-the- counter (otc) medicines as an antitussive (cough suppressant) and expectorant (an agent that promotes the removal of mucus from the respiratory tract). other medical uses of dxm include the temporary relief of sinus congestion, runny nose, cough, sneezing, itching of the nose and throat, and watery eyes caused by hay fever, allergies, cold, or flu (influenza). Approximately 70 dxm-containing products are available to consumers.