Traditional herbal strategies for treating lung disease are founded on supporting and tonifying the innate protective resources. This is one area where the divide between traditional and modern approaches is particularly great. There are very few modern endorsements of early treatment strategies. Modern medical science, which at first embraced such agents in the earlier part of this century, now sees no role for their use. For example, modern editions of Martindale’s Extra Pharmacopoeia claim that: “There is little evidence to show that expectorants are effective.” Some modern drugs may have expectorant activity, such as bromhexine, but they are usually referred to as ‘mucolytic’. The impact of traditional remedies on the respiratory system is relatively poorly researched. Reliable external measures of change in mucosal functions are elusive; many respiratory diseases are either self-limiting or are among some of the most persistent conditions in the clinic. (1)

However, while the traditional herbal approach is somewhat lacking in scientific support, it is not without a rational basis. This article will examine some important herbal concepts involved in supporting the innate defenses of the lungs during infection. The key concept of expectorants will be discussed in detail, with a focus on the classification of expectorants and the scientific investigations into their effects.

Part of the problem with expectorants probably arises from confusion over their definition. Another aspect of the dismissal of expectorants stems from the difficulties involved with measuring their efficacy.

The four definitions of expectorants given below highlight the difficulties. The dictionary meaning is only concerned with the actual oral production of phlegm or sputum. Since the majority of mucus produced from the lungs is swallowed, this definition is clearly unsatisfactory. Definitions from the pharmacologists Boyd and Lewis are more useful but probably the best definition comes from Brunton, a 19th century pharmacologist.

Oxford Dictionary “Promoting the ejection of phlegm by coughing or spitting.”

Boyd (1954) “An expectorant may be pharmacologically defined as a substance which increases the output of demulcent respiratory tract fluid.”

Lewis (1960) “Expectorants increase the secretions of the respiratory tract and so reduce the viscosity of the mucus which can then act as a demulcent. By virtue of the presence of increased quantities of fluid mucus, expectorants produce a “productive cough” which is less exhausting and less painful to the patient.”

Brunton (1885) “Remedies which facilitate the removal of secretions from the air passages. The secretion may be rendered more easy of removal by an alteration in its character or by increased activity of the expulsive mechanism.”

Why Expectorants?

Many respiratory conditions are characterized by abnormal mucus (catarrh) which can narrow airways. This abnormal mucus may be thick and tenacious and hence very difficult to clear from the airways. If expectorants can render this catarrh more fluid and/or assist in its expulsion, then a clinical benefit should be achieved.

Expectorants can help to relieve debilitating cough. The presence of an irritation in the airways (such as tenacious abnormal mucus) invokes the cough reflex. (The cough reflex is most sensitive in the trachea and larger airways. The sensitivity progressively decreases in the finer airways and in the very fine airways there is no reflex at all. So in alveolitis, there is little stimulation of the cough reflex, whereas for tracheitis the stimulus is strong). By clearing abnormal mucus or by changing its character and making it more demulcent, expectorants can allay cough and are therefore antitussive.

Classification of Expectorants (after Gunn, 1927)

The classification of expectorants by their mode of action is extremely valuable in understanding their appropriate use. In 1927 Gunn proposed four classes of expectorants. (2) A fifth class was suggested by the Russian scientist Gordonoff. (3)

1. Reflex expectorants

These are emetics which cause an increased secretion of respiratory tract fluid when given orally in subemetic doses. Act by reflex from the upper GIT mediated by the vagus nerve eg saponin herbs, Lobelia, Ipecac

2. Central expectorants

Act on the CNS. Possibly Ipecac

3. Parasympaticomimetics

Stimulate the vagus nerve eg Pilocarpus. Also capsaicin (in Capsicum) stimulates bronchial C-fibres

4. Stimulants of secretory cells

Act directly on goblet cells, eg essential oils

5. Secretomotorics (after Gordonoff 1938)

Stimulate mucociliary transport, eg camphor, thyme

From the herbal perspective the two most important classes are the reflex expectorants and the stimulants of secretory cells. The use of the terms stimulating or relaxing expectorants is no longer valuable, as the following quotation illustrates.