A cough medicine is a drug used to treat coughing and related conditions. Dry coughs are treated with cough suppressants (antitussives) that suppress the body’s urge to cough, while productive coughs (coughs that produce phlegm) are treated with expectorants that loosen mucus from the respiratory tract. These medicines are widely available in the form of cough syrup, also known as linctus.
Cough suppressants may act centrally (on the brain, and specifically the vagus nerve) or locally (on the respiratory tract) to suppress the cough reflex.
Centrally acting suppressants include dextromethorphan (DXM), noscapine, ethyl morphine and codeine.
Peripherally acting substances include local anaesthetics, which reduce the sensation of nerves in the throat, and demulcents, which coat the esophagus. Although it is commonly believed that cough medicines must coat the throat to be effective, there is no evidence that it is possible to control coughing by this means.
One might think it unwise to suppress the cough reflex (the mechanism for expelling mucus from the respiratory tract) but severe coughing may lead to lung irritation, causing a vicious cycle. The cough reflex is also very strong and cannot be completely suppressed. However, dry cough (without mucus production) or cough that is exhausting and preventing sleep should be treated with suppressants.
Recent studies have found that theobromine, a compound found in cocoa, is more effective as a cough suppressant than prescription codeine. This molecule suppresses the “itch” signal from the nerve in the back of the throat that causes the cough reflex. It is possible to get an effective dose from 50g of dark chocolate, which contains 2 to 10 times more cocoa than milk chocolate. Theobromine was also free from side effects in the blind tests.
An expectorant (from Latin ex- “out” + pectoris “of the chest”) is a medicine or herb which increases the expulsion of tracheal or bronchial mucus through expectoration or coughing. In over-the-counter preparations, guaifenesin is often used. The effectiveness of expectorants in cough medicines has been questioned; however, water is an effective expectorant and drinking adequate water thins the mucus and enables it to be expelled more easily.
Herbal remedies considered to be expectorants include the following:
- Aniseed (Pimpinella anisum),
Balm of Gilead (Populus gileadensis),
Balsam of Peru (Myroxylon perierae),
Balsam of Tolu (Myroxylon toluifera),
Bloodroot (Sanguinaria canadensis),
Cannabis (Cannabis Sativa),
Cardamom (Elettaria caradamomum),
Coltsfoot (Tussilago farfara),
Comfrey (Symphytum officinale),
Elderflower (Sambucus nigra),
Elecampane (Inula helenium),
Garlic (Allium sativum),
Golden seal (Hydrastis canadensis),
Grindelia (Grindelia camporum),
Hyssop (Hyssopus officinalis),
Iceland moss (Cetraria islandica),
Irish moss (Chondrus crispus),
Liquorice (Glycyrrhiza glabra),
Lobelia (Lobelia inflata),
Lungwort (Sticta pulmonaria),
Marshmallow (Althaea officinalis),
Mouse ear (Hieracium pilosella),
Mullein (Verbascum thapsus),
Pleurisy root (Asclepias tuberosa),
Senega (Polygala senega),
Skunk Cabbage (Symplocarpus foetidus),
Squill (Urginea maritima),
Thuja (Thuja occidentalis),
Thyme (Thymus vulgaris),
Vervain (Verbena officinalis),
White horehound (Marrubium vulgare),
Wild cherry (Prunus serotona).
Cough drops or throat lozenges are tablets which people can suck to soothe the throat or to alleviate excessive coughing. They are usually small, sweetened (often with artificial sweeteners), and contain an oral anesthetic, such as menthol, which anesthesizes the receptors in the throat that cause the cough reflex. The occasional use of “lozenge” (first used in 1530, according to the Oxford English Dictionary) is due to the original lozenge shape of cough drops. Popular brands of cough drops include Fisherman’s Friend, Halls, Ricola, and Luden’s.
In 2002, researchers at the University of Bristol (Schroeder & Fahey) published a study in the British Medical Journal indicating that some cough medicines are no more effective than placebos. In 2006, the American College of Chest Physicians published a guideline that had the dual message that many over-the-counter cough medicines are not effective and that those that are effective in treating the symptom do not treat the underlying cause; the underlying disorder emphasized by the guideline was pertussis (whooping cough) in the elderly. This guideline has been referred to by many news articles in the lay press, which emphasize the economic impact of discouraging cough medicine use while not touching on the health concerns expressed.
Many cough mixtures contain both an expectorant and a suppressant — even though an expectorant requires the action of a cough to expel mucus. Many believe this supports the idea that cough suppression is just a placebo effect. However, in practice the two active ingredients combine to provide less coughing, but more productive coughs.
Colloquial term usage
“Cough medicine”, for example “Grandpa’s old cough medicine”, is also a commonly used euphemism for whiskey and other strong alcoholic beverages, or even actual cough medicine such as NyQuil which in some formulations has a high alcohol content.
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