Cough is a forceful release of air from the lungs. Coughing protects the respiratory system by clearing it of irritants and secretions.
Basically, there are two kinds of cough: productive and non-productive.
Productive cough (Wet Cough): A productive cough (chesty cough) is typically associated with a viral upper respiratory tract infection (URI), such as the common cold. Infection causes the mucous membrane of the bronchial tubes to become inflamed and produce thick, sticky mucus, so that it is no longer removed by the normal action of the cilia and clogs up the airways. Coughing is a reflex that expels this sticky mucus, also called phlegm. Inflammation and accumulated mucus narrow the airways, restrict respiration, and can promote bacterial infection.
Non-productive cough (Dry cough): A non-productive cough is dry, tickling and irritating - a repeated stimulus in the respiratory tract and usually without expectoration. This cough can for example be caused by cigarette smoke or dust. It can also have an allergic or neurotic origin or can be caused by other perhaps more severe diseases.
Cough medications are grouped in to two types - Antitussives and Expectorants.
Expectorants (Expels mucus, phlegm) are mediations which promotes or facilitates the secretion or expulsion of phlegm, mucus, or other matter from the respiratory tract Or in other words expectorants make cough up mucus easier and less irritating. Usually expectorants are used to treat productive cough. Ex. Guaifenisin
Antitussives (Cough Suppressants) suppress the cough reflex by depressing the medullary cough centre or associated higher centres in the brain and/or peripheral cough receptors - resulting in calming down the cough. Antitussives are used for treating Nonproductive (dry) cough. Cough suppressants simply lessen the urge to cough. They should not be used if the cough is wet sounding and produces mucus. Examples of antitussives are codeine,hydrocodone,dextromethorphan etc.
Coughs associated with colds should be treated with an expectorant to clear out mucus.A productive cough is the body's way of clearing out mucus. An expectorant encourages the body to get rid of the phlegm quickly and get over the coughing. Suppressants, on the other hand, suppress the body's natural desire to healing by blocking the cough reflex.