(verify) Dextromethorphan ( DXM or DM ) is an antitussive (cough suppressant) drug . It is one of the active ingredients in many over-the-counter cold and cough medicines, such as Mucinex DM, Robitussin , NyQuil , Dimetapp , Vicks , Coricidin , Delsym , and others, including generic labels. Dextromethorphan