Robitussin DM is used to relieve congestion and coughing caused by the common cold, according to WebMD. The active ingredient dextromethorphan acts as a cough suppressant, while guaifenesin acts as an expectorant by loosening mucus for easier expulsion.
Robitussin DM should be used according to directions to avoid serious side effects, according to WebMD. It should only be used in patients over 6 years of age, and it should not be used in conjunction with other cold or cough medications. Additionally, Robitussin DM should not be used by patients who are also taking MAO inhibitors, according to Drugs.com. If a cough persists for longer than 7 days, the patient should seek medical attention.