Coughs are one of the most common symptoms of the common cold, which is a viral disease. Since it is caused by a virus, antibiotics aren't effective against the common cold. Over-the-counter cough medications, such as decongestants and pain relievers, offer only temporary relief of symptoms, but they do not shorten the length of time you are sick, according to MayoClinic.com.
An expectorant is an agent that promotes the discharge of mucus from the respiratory tract. It treats moist coughs by liquefying the hard-to-shift mucus in the lining of the lung and promotes its expulsion.
The chief ingredient of all expectorants is guaifenesin, which is mixed in with demulcent, an oily substance containing glycerin or glucose to coat and soothe the throat, explains FamilyDoctor.org.
Cough suppressants, also called antitussives, relieve coughing by suppressing the function of the center in the brain that controls the cough reflex, according to FamilyDoctor.org. Dextromethorphan is a common antitussive that reduces only dry and hacking coughs associated with common colds. Over-the-counter cough suppressants can help treat severe coughs that interfere with nighttime sleep.
Dextromethorphan and guaifenesin may be combined with each other and in combination with other drugs, such as pain relievers, decongestants or antihistamines. These products are called multi-symptom cold medicines, and they treat such symptoms as a body aches, fever, sore throat and headache associated with a cold. But if your primary symptom is coughing, the drying effect of antihistamines and decongestants in combination medicines may make mucus thicker and harder to clear, which can make coughing worse, according to FamilyDoctor.org.