H 25 N O Brief Description: 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  Robitussin ,  NyQuil ,  Dimetapp ,  Vicks ,  Coricidin ,  Tussin ,  Delsym , and others, including  generic  labels. Dextromethorphan