Mucinex DM Share definition Flag Expectorant/cough suppressant containing 60 mg extended-release bi-layer dextromethorphan HBr tablets. Also contains 1200 mg guaifenesin. Active ingredients also found in Mucinex DM, Delsym, NyQuil, etc. Mucinex DM by kolonoman February 25, 2009 Get the Mucinex DM mug.