The active ingredients in Mucinex DM are guaifenesin 1200 milligrams and dextromethorphan HBr 60 milligrams. Mucinex DM is an expectorant and cough suppressant.
According to WebMD.com, Mucinex DM is a combination medication used to relieve the symptoms caused by various breathing illnesses. The drug relieves cough caused by bronchitis and common cold by thinning and loosening the mucus in the airways. The dextromethorpan in Mucinex DM works as a cough suppressant. This medication is available without prescription and is not recommended for children under age 12. Recommended dosage is based on the medical condition, age and response to treatment. The manufacturer recommends not to take more than two doses in 24 hours.