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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.
Cough suppressants
Cough suppressants may act centrally (on the brain) 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.
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 dark chocolate, which contains more cocoa than milk chocolate. Theobromine was also free from side effects in the blind tests.
Expectorants
An expectorant 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. Herbal expectorants include the following:
- Aniseed (Pimpinella anisum),
- Balm of Gilead (Populus gileadensis),
- Balsam of Peru (Myroxylon perierae),
- Balsam of Tolu (Myroxylon toluifera),
- Blood Root (Sanguinaria canadensis),
- Coltsfoot (Tussilago farfara),
- Comfrey (Symphytum officinale),
- Elder Flower (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
Cough drops are tablets which people can suck to soothe the throat or to alleviate excessive coughing. They are usually relatively small, sweetened, and contain medicine that helps to reduce pain or irritation. 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 (cough drop), and Ricola.
Controversy
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.
Some cough mixtures contain both expectorants and suppressants in their active ingredients - again suggestive that they are primarily placebo in their effect.
References
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