Guaifenesin is the only expectorant approved by the Food and Drug Administration (FDA). The exact way Mucinex works is unclear. However, it has several significant effects, including the following ...

If you have a bottle of Mucinex in your medicine cabinet ... reducer), dextromethorphan (cough suppressant), guaifenesin (expectorant), phenylephrine (decongestant), and diphenhydramine ...