Mucinex contains the drug guaifenesin, which is an expectorant that loosens mucus. This makes it easier for the body to expel mucus and subsequently relieves congestion, according to the Mucinex website. Certain types of Mucinex, such as Mucinex DM, also relieve coughing due to the dextromethorphan they contain.
Although guaifenesin helps thin mucus and relieve chest congestion, the medicine does not relieve the problems that cause the mucus buildup in the first place, notes MedlinePlus. In fact, expectorants such as guaifenesin make patients cough in order to rid the air passages of mucus, explains WebMD. However, coughing subsides once the air passages are cleared.
Guaifenesin comes in the form of tablets, capsules or syrups, such as Mucinex, states MedlinePlus. It should be taken with plenty of fluids, as drinking water is also an effective way to clear mucus, according to WebMD.
The Mucinex ingredient dextromethorphan relieves coughing by decreasing the activity in the area of the brain that causes coughing, explains MedlinePlus. Like guaifenesin, dextromethorphan only treats symptoms and does not treat the underlying cause of the coughing.
Although recommended doses of dextromethorphan are safe for consumption, large amounts of the medicine can cause serious side effects or even death, reports MedlinePlus. Because many over-the-counter cold and flu medicines contain dextromethorphan, MedlinePlus strongly suggests reading the labels carefully when administering more than one medicine at a time.