Some coughs serve a useful purpose, for example to get rid of something that has ‘gone down the wrong way’ or to cough up phlegm.  Common causes of coughing include infection of the bronchial tubes (bronchitis), inflammation of the air passages that occurs in asthma and breathing irritants (e.g. smoking). Coughs, like the ones you get with colds, are caused by a virus infection and are often just dry and irritating, serving no useful purpose.  Most acute coughs clear up on their own and are usually associated with a cold.  However, most long-standing coughs occur in smokers and in people the bronchitis and other chronic chest disorders.

When the chest is congested (e.g. acute bronchitis) we develop a rattly cough on the chest (a congestive cough) and may cough up phlegm (a mixture of mucus and pus).  We describe this as a productive cough (i.e. a cough that produces phlegm when we cough).  A dry cough not associated with congestion of the chest and producing no phlegm is called a non-productive cough.  Congestion of the chest may produce a rattly cough which is also non-productive.

A congestive cough on the chest is helped by anything that ‘loosens’ the phlegm and makes it easier to cough up.  Avoiding dry atmospheres, stopping smoking, drinking more fluids than normal and using steam inhalations are all beneficial, provided of course that any underlying infection, inflammation and wheezing are treated effectively.  If these actions are taken, there may be no need to take cough medicine that is supposed to ‘loosen’ the phlegm and/ or increase its production.

A dry, irritating, non-productive cough will also benefit from avoiding dry atmospheres, stopping smoking, drinking more fluids than normal and using steam inhalations.  It may also benefit from the use of a cough suppressant.

Cough medicines

There are three main types of cough medicine: soothing cough medicines for throaty coughs; ones that stop you coughing (cough suppressants or antitussives); and ones that are supposed to enable you to cough up phlegm more easily, called cough expectorants.

Soothing cough medicines

We spend millions of euros every year on cough lozenges, pastilles and syrups to relieve dry coughs produced by irritation in the throat (often referred to as ‘throaty’ coughs).  These are nearly always associated with a cold and last for only a short period of time – usually no more that a day or two.

Soothing cough medicines (lozenges, pastilles and syrups) contain sweet substances such as sorbitol, glycerol and syrup, and in addition they contain mixtures of chemicals such as peppermint, eucalyptus, lemon, clove, aniseed, menthol and camphor.

Soothing cough medicines coat the surface of the throat and protect it from irritation. They also make you produce more saliva which is the body’s natural protection against irritation of the throat.  It is probably this increase in the production of saliva that really helps to soothe your throat.

WARNING Because of the high sugar content of some soothing cough medicines and the fact that you take them between meals, they may be harmful to teeth, particularly in children.  They should not be taken by diabetic patients.

Cough suppressants

The throat and air passages are very sensitive to irritation, which triggers messages up to the brain where they are picked up in a special nerve centre called the ‘cough centre’.  The cough centre responds by sending messages back down to the nerves supplying the muscles of the chest wall, abdomen and diaphragm to tell them to contract; this produces a cough.  This reflex may be very useful if you have inhaled something (note how you cough if something has ‘gone down the wrong way’).  However, it may be very annoying if you have a cold or some other disorder that makes you keep coughing all the time.

There are several effective drugs available which reduce the sensitivity of the cough centre and stop it sending messages out to cough.  In other words, they suppress your cough.  There are two groups of cough suppressants – those that may produce addiction and those that do not.  They are used to relieve coughs that do not produce phlegm (non-productive coughs).

Cough suppressant drugs that may produce addiction (narcotic cough suppressants)
Diamorphine (heroin), methadone and morphine are narcotics which are very effective in suppressing coughs.  Their use should be restricted to treating severe coughs; for example, in patients dying from cancers of the lung.  In the doses used to treat coughs they affect the brain and may produce drowsiness, they may also cause constipation, depression of breathing and difficulty in urinating.

Codeine is obtained from opium or made from morphine.  Two salts of codeine (codeine sulphate and codeine phosphate) are used as cough suppressants.  One or other appears in numerous cough medicines.

Codeine is a moderately effective cough suppressant.  It may produce drowsiness, dizziness, nausea and constipation (which may be a particular problem in the elderly).  Large doses may produce excitement, and in children convulsions may occur.  Some patients may be allergic to codeine and develop nettle rash (urticaria) and itching skin (pruritus).  If high, regular, daily doses of codeine cough medicine are used there is a risk that some individuals may come to ‘rely’ on the medicine and start having to increase the dose because not only are they becoming tolerant to the effects of codeine but they are also becoming addicted to it.  Babies have been born addicted because their mothers took codeine cough medicine daily during pregnancy.  Codeine and other narcotic cough suppressants should not be given to children under one year of age.

Cough suppressant drugs that do not produce addiction but that are weaker than codeine
Pholcodeine is related to morphine.  It may produce nausea and drowsiness.  In high doses it may produce restlessness, excitement and lack of control over voluntary movement, producing, for example, difficulty in walking.

Dextromethorphan is nearly as potent as codeine but produces fewer harmful effects.  It may cause drowsiness, dizziness, excitation, mental confusion, and stomach upsets.  Very high doses may depress the rate and depth of breathing.

Noscapine is obtained from opium.  It has no relieving properties and is not a drug of addiction, but is as effective as pholcodeine.  It may produce slight drowsiness, dizziness, headache and nausea, and it may cause allergic symptoms affecting the nose, eyes and skin.

Isoaminile is as effective as pholcodeine.  It may produce dizziness, nausea, constipation and diarrhoea.

Choosing a cough suppressant

For a dry, irritating, throaty cough associated with a cold there is seldom any need to take a cough suppressant.  Sucking a sweet, whether medicated or not, will help because it will increase the production of saliva which will soothe the throat.  If this does not work or the irritation is below the voicebox (where soothing cough lozenges, pastilles and syrups can have no effect because they are swallowed into the stomach), avoiding dry atmospheres, stopping smoking, drinking more fluids than normal and using steam inhalation will normally help.  If this does not work or is inconvenient, it may be worth trying a cough suppressant, particularly if a dry, irritating cough is disturbing your sleep.  Choose a cough medicine that contains only one cough suppressant in an effective dose; for example, codeine or one of the following – dextromethorphan, isoaminile, noscapine or pholcodeine.  There is little to choose between the latter provided they are taken in effective cough-suppressant doses.  One dose should provide relief for up to 4 hours.  With most acute coughs there is no need to take more than three or four doses daily for more than 2 to 3 days.

Cough expectorants

Our traditional liking for cough medicines goes back to the days when there were no antibiotics, and tuberculosis (consumption), bronchitis and other chest diseases were rife in Ireland.  Doctors were able to do very little but prescribe bottles of brightly coloured medicines, which if they tasted awful were supposed to do you good!  Paradoxically, despite the availability today of specific and effective treatments for these disorders the use of cough medicines continues, principally due to heavy advertising by drug companies and our faith in them.

Cough expectorant drugs are supposed to help you cough up phlegm by increasing its production but there is little evidence of such beneficial effects.  There is evidence that they irritate the lining of the stomach and that in high doses this irritation will stimulate the vomiting centre in the brain to make you vomit.  However, there is doubtful evidence that if they are taken in a dose not big enough to make you vomit that they stimulate, by a reflex mechanism, the cells in the bronchial tubes to produce more secretions that will soften the phlegm and make it easier to cough up.  Yet this is the belief, even though it has never been convincingly proved that any of theses drugs can help you cough up phlegm.  Despite this there are several drugs marketed for this purpose.  They include acetic acid, ammonium salts, bromhexine, camphor, cocillana, creosote, guaiacol, guaiacol carbonate, guaiphenesin, iodides, ipecacuanha, liquorice, senega, squill and terpin.

These various chemicals used as expectorants may irritate the lining of the stomach and in high doses produce nausea and vomiting.  They should be used with caution by people who suffer from peptic ulcers.

Harmful effects of cough expectorants

Ammonium chloride and other ammonium salts in large doses may produce vomiting, nausea, thirst, headache, rapid breathing, progressive drowsiness, make the blood acid (acidosis) and cause a fall in potassium. Guaiacol may cause drowsiness.

Liquorice may cause salt and water to be retained from the urine and a loss of potassium in the urine.  These effects may cause fluid retention in the body, raised blood pressure and disturbances in the chemistry of the blood.

Iodine as potassium iodide or sodium iodide is present in some cough medicines as an expectorant.  The risks of regular daily use of cough medicines containing iodides include mental depression, nervousness, insomnia, sexual impotence, and under-activity of the thyroid gland.  Goitres may occur in infants born to mothers who took cough medicines containing iodides regularly every day during pregnancy.  Allergy may occur to iodides (iodism) and cause symptoms like a common cold – headache, pain and swelling of the salivary glands, watery eyes, weakness, conjunctivitis, fever, laryngitis and bronchitis.

Skin rashes may occur such as a mild redness of face or acne of the face.  

Ipecacuanha is of interest because it is used as a drug to make you vomit if you have taken an overdose of certain drugs (e.g. alcohol).  It contains two drugs – emetine and cephaeline.  It is irritant to the lining of the stomach and intestine, and in high doses it may produce vomiting, bloody diarrhoea and ulceration of the stomach and/ or intestine.  Such high doses may also damage the kidneys, producing proteins in the urine, and may be toxic to the heart.

Squill irritates the lining of the stomach, and in high doses it may produce nausea, vomiting and severe diarrhoea; it may also affect the heart, producing effects like those produced by digoxin.  Cough medicines contain squill should not be taken by patients with kidney or heart disorders.

Other drugs used in cough medicines

Numerous other drugs are included in cough medicines despite the fact that there is no convincing evidence that they are of any benefit other than improving the colour, taste or smell – they include benzoic preparations, camphor, eucalyptus oil, menthol, peppermint oil, and pine tar, sodium citrate, tolu and turpentine oil.

The use of antihistamine drugs in cough medicines

Antihistamine drugs used in cough medicines include chlorpheniramine, diphenhydramine, pheniramine, promethazine and tripolidine.  They produce two effects that are exploited in cough medicines – they act on the brain, producing drowsiness and a damping down of the cough centre, and they dry up the lining of the nose and breathing passages.

Warnings The drowsiness produced by antihistamines included in cough medicines may affect your ability to drive motor vehicles and operate moving machinery.  Antihistamines may also increase the effects of alcohol, sleeping drugs, tranquillizers and narcotic pain relievers.  Furthermore, their effects on drying up the lining of the breathing passages may actually make it harder for you to cough up phlegm if you have congestion on your chest.

The drowsiness produced by antihistamines may interfere with breathing in people who suffer from chronic bronchitis and other serious chest disorders because it may cause a build-up of carbon dioxide in the blood.

The use of bronchodilator drugs in cough medicines

Irritation of the lining of bronchial tubes may cause them to constrict, which may cause coughing.  For example, a cough may be an early symptom of asthma or allergy.  In a cough of this kind it is important to take an effective dose of a drug that dilates the bronchial tubes, a bronchodilator, and to treat any associated infection and / or inflammation or allergy.  The bronchodilators used in cough medicines are usually present in such small doses as to be of little  benefit if you suffer from asthma or some other wheezing disorder.  Furthermore, if you do not suffer from a wheezing disorder they are of doubtful value.

The use of decongestant drugs in cough medicines

Decongestant drugs are included in some cough medicines.  The three most commonly used are pseudoephedrine, phenylephrine and phenylpropanolamine.  They are usually present in very small doses but if you overdose or use a nasal decongestant that contains one or more of these drugs at the same time, you may develop toxic symptoms, which include headache, nausea, vomiting, sweating, rapid beating of the heart, palpitations, muscle weakness, restlessness, anxiety, insomnia and difficulty passing urine.

The use of anticholinergic drugs in cough medicines

Anticholinergic drugs dry up the lining of the air passages and dilate the bronchial tubes.  Because they dry the air passages, they make it more difficult to cough up phlegm.

Warning Any cough medicine that contains a decongestant, antihistamine and/ or anticholinergic drug may make it more difficult to cough up phlegm.

Drugs that reduce the stickiness of phlegm and make it easier to cough up

Drugs that reduce the stickiness of phlegm are called mucolytics.  They reduce the stickiness of sputum and help to liquefy the phlegm. Mucolytic drugs may be taken by inhalation or by mouth.

Inhalation mucolytics  Acetylcysteine is the one used most frequently but there is doubt about its effectiveness by inhalation, which may cause wheezing in some individuals particularly those who suffer from asthma.

Mucolytics that may be taken by mouth include carbocisteine ( Benylin Clear Action, Exputex, Mucodyne, Pulmoclase) and methylcysteine ( Visclair).  However, there is controversy over how much people benefit from their use even though they do liquefy the sputum.

Cough mixtures (compound cough medicine)

Cough mixtures contain small doses of several drugs aimed at reducing coughs.  They are very popular however some mixtures are quite irrational – combining a cough suppressant to stop you coughing with a cough expectorant to help you cough, or mixing small doses of a large number of drugs that produce the same effects.

Advice on treating coughs

For a dry irritating cough caused by a cold that is interfering with your sleep or disrupting your day it is best to use a cough medicine that contains a single drug ( e.g. codeine linctus).    

For a chesty rattly cough ( congestive cough) where it is difficult to cough up phlegm, cough medicines are of little use even though they are supposed to ‘loosen’ the phlegm and make it easier to cough up.  It is far more important to drink more fluids than usual and to use water or steam inhalations; to avoid dry, smoky atmospheres; to stop smoking if you smoke; to check whether any drug you are taking may dry up your bronchial tubes; and to seek medical advice and have specific treatment any wheezing that may be due to infection and/ or inflammation of the bronchial tubes.

Always seek medical advice for any cough that persists for more than 2 or 3 days, if your phlegm is yellowish – green or if it is bloodstained and/ or if you have a fever associated with your cough.

Reducing the risks of cold and cough mixtures

If you still wish to take a cold and/ or cough mixture be guided by the following warnings.

If you are on a low salt diet, a low sugar diet ( e.g. if you are a diabetic), if you are allergic to any preservative or dyes in medicines or if you are allergic to any of the drugs included in cough and cold medicines, check with your pharmacist before purchasing a cold or cough mixture.

Cold and cough mixtures contain more than one active drug and many liquid cough mixtures contain alcohol; therefore check with your pharmacist if you wish to avoid using a cough mixture that contains alcohol or a drug that may cause a problem for you.

If you are pregnant or breastfeeding it is safest to avoid the use of drugs if possible.  It is certainly safer to avoid the use of mixed drugs.

Be most cautious about using cold and cough mixtures if you suffer from diabetes, asthma or other chronic chest disorders, enlarged prostate gland or any difficulty in passing urine, any disorder of the heart or circulation, raised blood pressure, kidney or liver disease or over-active thyroid gland.  Consult your pharmacist before purchasing a preparation.

Always check with your pharmacist whether it is safe to take a cough or cold remedy along with alcohol or any other drug treatment you may be taking, whether prescribed by your doctor or purchased by you ‘over-the-counter’.

Always ask your pharmacist for clear instructions on how to take a cold or cough remedy.  Always take the stated dose; do not overdose because you will increase the risk of harmful effects.

Never take more than one cough or cold remedy or pain reliever without checking that it is safe to do so.

Remember that some cold and cough remedies may contain a drug that can irritate the stomach ( e.g. aspirin).  Such preparations should be taken with or after food and not on an empty stomach.  Check with your pharmacist.

Sustained-release capsules or tablets should be swallowed whole and not chewed before swallowing.

It is not important if you miss out a dose of a cough or cold remedy.  Take it as soon as possible; but if it is nearly time for your next dose, skip a dose.  Never take a double dose in order to catch up.

Always keep cough and cold remedies out of reach of children and away  from heat and direct light but not in the bathroom where heat and moisture can cause the drugs to break down.

Do not keep out-of-date cough and cold remedies return them to your pharmacist for disposal.