Mucinex D is a medicine used in the treatment of cough and congestion. However, the medicine may not be used for cough and congestion caused by emphysema, smoking, or asthma. The medicine has two active ingredients, dextromethorphan and guaifenesin, each of which works by different but complementary means.
Dextromethorphan is a cough suppressant; whose mechanism of action involves affecting many different areas of the neurotransmitter system such as serotonin. In contrast, guaifenesin is an expectorant, a drug which helps to loosen mucus and expel it from the body.
Common side effects associated with Mucinex D include dizziness, drowsiness, diarrhea, and feeling nervous.