A cough occurs as an involuntary reflex to protect the airways from foreign substances and excessive mucus. The airways contain tiny hair-like projections known as cilia. When the cilia become irritated, it stimulates the nerve endings and triggers the cough reflex. Doctors classify coughs as acute, sudden onset and short-lasting, and chronic, defined as a cough lasting longer than four weeks, according to the Merck Manual. Because so many types of cough medications exist, choosing the right active ingredient depends upon the type of cough and underlying cause.
Types of Cough
In addition to acute and chronic coughs, doctors also classify coughs as a dry, also referred to as hacking, cough or a wet, also known as a productive, cough. A wet cough usually occurs when excess mucus builds up in the airways. A dry cough occurs as a result of an inhaled irritant. In either case, once the nerves in the upper airways become activated, the coughing reflex occurs.
Cough Causes
The nose and mouth lead to the trachea, which branches into the two bronchi--the tubes that lead to the lungs. The bronchi branch into small tubes known as the bronchial tubes and then into even smaller tubes known as the bronchioles. Mucus, a slimy substance, lines all of the airways in order to protect the lungs from foreign invaders such as dirt, bacteria and viruses. Too much mucus, however, irritates the airways and triggers a wet cough to try to expel mucus. Inhaled irritants, such as air pollution, cigarette smoke, chemicals and pollen particles disrupt the cilia in the airways and trigger the cough to prevent them from entering the lungs.
Antitussives
An antitussive describes a cough suppressant that relieves coughs by blocking the cough reflex. Many over-the-counter cough suppressants contain the active ingredient dextromethorphan. Some formulations combine this active ingredient with other medications such as pain relievers, decongestants or antihistamines. Doctors recommend not using antitussive active ingredients to treat wet sounding coughs because the body needs the cough reflex to get rid of the excess mucus, according to the University of Iowa Hospitals and Clinics.
Expectorants
Guaifenesin, an active ingredient classified as an expectorant, thins the mucus lining of the airways so coughs can remove the irritating mucus. Without the excess mucus irritating the nerve endings, the cough subsides. Expectorants, found in many over-the-counter formulas, should therefore be used to treat a wet-sounding cough.
Prescription Strength
For severe or chronic coughs, doctors can prescribe prescription-strength cough medicines. Prescription cough medications often contain the active ingredient hydrocodone or promethazine. Although doctors usually prescribe medications containing hydrocodone, classified as an opiate analgesic, to relieve pain, it also decreases activity in the part of the brain that controls cough, therefore acting as an antitussive agent, according to the U.S. National Library of Medicine. Promethazine blocks the action of certain natural substances in the body therefore reducing symptoms of allergic reactions, treating nausea, providing sedation and relieving coughs, as described by the U.S. National Library of Medicine.
