Common side effects of Mucinex include nausea and vomiting, explains Drugs.com. People who are allergic to Mucinex can have several symptoms, such as difficulty breathing, hives, rash, chest tightness and swelling of the lips, tongue or mouth.
Doctors prescribe Mucinex to ease the symptoms of mucus and cough caused by hay fever, flu or colds, according to Drugs.com. This medication works by thinning mucus and making it easier for patients to cough. Patients should take Mucinex by mouth with or without food as directed by a doctor. They should drink a lot of water while taking the drug and should avoid breaking, chewing or crushing it.