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Robitussin DM™, Cough Relief DM™. Dextromethorphan (dex-troe-meth-OR-fan) and Guaifenesin (gwye-FEN-e-sin) is an antitussive-expectorant combination cough medication. Antitussives act directly on the cough center in the brain. Expectorants work by loosening the mucus or phlegm in the lungs. In general, the best thing you can do to loosen mucus or phlegm is to drink plenty of water. To help loosen mucus or phlegm in the lungs, drink a glass of water after each dose of this medicine, unless otherwise directed by your doctor.

Last Updated: 12/17/08