Cough medicine

Overview
A cough medicine is a medicinal 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
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 oesophagus. One category of peripherally acting substances is vapor-administered, such as Vicks VapoRub. Camphor is an active ingredient (along with menthol) in vapor-steam products and it is effective as a cough suppressant. Although it is commonly claimed that liquid 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, a dry cough (without mucus production) or a cough that is exhausting and prevents sleep should be treated with suppressants.

Recent studies have found that theobromine, a compound found in cacao, is more effective as a cough suppressant than prescription codeine. This compound 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 (1 g, though 0.5 g may be sufficient, according to PMID 15548587) from 50g of dark chocolate, which contains 2 to 10 times more cacao than milk chocolate. Cocoa powder contains roughly 0.1 g per tablespoon (5g). Theobromine was also free from side effects in the blind tests.

Expectorants
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. Guaifenesin is often used in over-the-counter preparations, and is commonly combined with other medications designed to relieve various cold-related symptoms (including cough suppressants, decongestants, antihistamines and pain relievers/fever reducers).

Cough drops
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 Ricola, Fisherman's Friend, Halls, Vicks, Strepsils and Luden's.

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 for acute coughs in adults, including coughs related to upper respiratory tract infections. 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.

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.

Mass poisonings due to diethylene glycol
According to the New York Times, at least eight mass poisonings have occurred as a result of counterfeit cough syrup, mostly if not totally produced in China, substituting inexpensive diethylene glycol in place of glycerin. Recently, 365 deaths were reported in Panama associated with cough syrup laced with diethylene glycol.

Colloquial 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. Rock candy dissolved in whiskey was once a common home-made cough medicine.