The uses of thyme, Thymus vulgaris and other Thymus species are well known, and extensive parts of the world get benefit from this plant group in medicinal and non-medicinal respects. Following the development of the medicinal uses of thyme we can see that thyme has changed from a traditional herb to a serious drug in rational phytotherapy. This is due to many pharmacological in vitro experiments carried out during the last decades, and even a few clinical tests. The studies have revealed well defined pharmacological activities of both, the essential oils and the plant extracts, the antibacterial and spasmolytical properties being the most important ones. The use of thyme in modern phytotherapy is based on this knowledge, whereas the traditional use of thyme describes only empirical results and often debatable observations. Therefore it seems necessary to present here the data available on the pharmacodynamics of thyme and thyme preparations in order to substantiate the use of thyme in modern medicine.
The non-medicinal use of thyme is no less important, because thyme (mainly Thymus vulgaris) is used in the food and aroma industries. It serves as a preservative for foods and is a culinary ingredient widely used as seasoning in many parts of the world. This use is due to the typical aroma of the plant which the essential oil is responsible for, and most people are very familiar with its typical smell. The special aroma also causes the role of the essential oil as a raw material in perfumery and in everyday cosmetics. The use of thyme as a preservative of food can be put down to the antioxidative effects of the plant extracts, which were of increasing interest in the last years. The results of these studies may be of further importance assuming that free-radical generation causes oxidative stress when it exceeds the capacity of antioxidant defenses in the human body. This way it may significantly contribute to pathogenesis.
Irrespective of the pharmacological and non-pharmacological effects when we examine and discuss the use of thyme we must take into account the chemistry of the plant. Therefore most of the studies described here refer to the chemical components of thyme.
The Therapeutical Uses of Thyme
The Traditional Use of Thyme in Folk Medicine
The widespread use of thyme dates back to ancient Egypt where various species of thyme were grown to perfume unguents and for embalming and, one can suppose, for medicinal purposes as well. The Greeks and the Romans used it in the same way, how and for what, we know thanks to Plinius (First century), Dioscorides (First century) and Theophrastus Bombastus von Hohenheim (Paracelsus 1493/94—1541). However the use of this plant did not extend further than the Alps until the eleventh century. The first northern chronicles, relating to this period, can be read in the “Physika” by the abbess Hildegard von Bingen (1098—1179) and in the works of Albertus Magnus (1193—1280). All the posterior works come from the Herbal written by the herbalist P. Mathiolus (1505—1577). The knowledge of traditional medicine is based on his works, in which the strength and efficacy of thyme were mentioned first. From then on numerous therapeutical properties have been attributed to thyme on a more or less empirical and debarable basis.
So many beneficial effects have been attributed to thyme that Bardeau (1973) stated thyme to be “an indispensable plant which should be consumed to conserve health. Furthermore, if one could replace one’s morning cup of coffee with an infusion of thyme, you would quickly appreciate its positive effects: animation of spirit, sensation of lightness in the stomach, absence of morning cough, and its euphoriant and tonic effect”. The readership will understand that it is impossible and not useful to enumerate all therapeutical benefits attributed to thyme which can be found in numerous popular works in folk medicine. Therefore only a selection of external and internal applications and indications shall be described, especially those which seem to be the most plausible ones.
Externally, infusions and the essential oil of thyme is traditionally used in treating injuries, bruises, infected ulcers, abscesses, cutaneous ulcers, various types of dermatitis, and in certain cases pruritis. Emulsions are useful when used in massage on rheumatic types of pain (sciatica, arthritis, lumbago), gout and neuritic pains. As regards the capillaries, thyme improves blood flow and the oxygenation of the scalp, reduces seborrhoea, regenerates the capillary glands, improves the state of the hair, prevents baldness, and is therefore useful in cases of alopecia. Baths of thyme possess invigorative and sedative properties, also behaving as coadjuvants in slimming cures.
The internal use of thyme is highlighted in the treatment of a variety of illnesses of the respiratory tract because of its expectorant, spasmolytic and antiseptic properties, such as flu, colds, sinusitis, chronic and acute bronchitis, tuberculosis, calming convulsive coughs (pertussis), and irritable and spasmodic coughs (asthma). It is attributed as having general stimulant properties, acting as a nervous tonic and being used in asthenic states. It is also useful in combatting insomnia, anxiety and depression.
Moreover it is used in a wide variety of gastro-intestinal troubles like dyspepsia (slow digestion), colic, fermentation, flatulence, diarrhea, gastritis and gastric ulcers. It is also useful in treating bacterial and parasitical infectious processes (Ascaris, Oxyuris, Taenia) (). In the genitourinary system the use of thyme for its diuretic, antiseptic and emenagogic properties is appreciated. In the cardiovascular system thyme helps the circulation, behaving like a hypocholesterolemic agent.
Thyme in phytotherapy
Although for thousands of years plants have been used as remedies, a controversial discussion of their usefulness has arisen in the last two decades. This is due to the knowledge that chemical substances are responsible for the pharmacological effects in the human body and additionally due to the detailed knowledge on their pharmacological mechanisms in human cells, tissues, and organs. Therefore in modern medicine the tendency has developed that only chemically defined and pure substances should be applied, exclusively such substances whose positive (curing) effects have been proved in clinical tests. Moreover, an optimal “package” for the chemicals is required which guarantees the liberation of the drug after application meaning highly developed drug technologies such as tablets, capsules, suppositoria, etc. Within this concept medicinal plants and herbal drugs cannot easily find consideration, because their chemical compositions represent very heterogeneous systems and, additionally, these complex mixtures are inadequately packed in vegetable cells.
However the increasing consciousness for health and environment results in the fact that people have not forgotten the herbal drugs. Quite the opposite has happened, globally an increasing demand for herbal medicines can be registered. This trend has also been accepted by the orthodox medicine remembering the benefit of traditional medicine lasting for centuries; but in modern medicine one cannot stick only to traditional uses. In order to concede the herbal remedies a “real-drugs” status, many scientific efforts have been and have to be made, and phytotherapy has developed into “rational phytotherapy”, a part of a scientifically-oriented medicine.
Legal regulations in Germany and Europe for drug registration ask for a proof of quality, safety and effectiveness. The latter has been evaluated for many herbal drugs, also for the herbs of Thymus vulgaris (common thyme) and Thymus serpyllum (wild thyme). A critical investigation of all the bibliography dealing with the chemistry and pharmacology of these two herbal drugs resulted in two “positive” (approved) monographs elaborated by a German expert group. The so-called Commission E Monographs represent a valuable therapeutic guide to herbal medicines in phytotherapy. Within the paragraphs “Uses” of these monographs the application of thyme and thyme preparations is only recommended for the treatment of some clearly-defined diseases, reading as follows:
(Common) Thyme — Thymi herba. External use: bath additive as a supporting cure of acute and chronical diseases of the upper respiratory tract; in addition against pruritus of dermatosis. Internal use: can be applied against symptoms of bronchitis and whooping cough. Catarrhs of the upper respiratory tract.
Wild thyme — Serpylli herba. External use: bath additive as supporting cure of acute and chronical diseases of the upper respiratory tract. Internal use: catarrhal infections of the upper respiratory tract.
Compared with the traditional uses of thyme the Commission E monographs obviously allow only restricted applications of thyme. These regulations must be followed when drug manufacturers apply for a registration of their phytotherapeutics as drugs. However, in serious publications on phytotherapy the area of application of thyme preparations is described similarly limited with special reference to the essential oil which can be used as bath additive (in mixtures) or for inhalation. It is recommended for a treatment of cough and sinusitis and its effects are described as secretomotoric, bronchospasmolytic and antibacterial. Thymol is proved to be responsible for these effects.
The essential oil of thyme can be administered in diverse galenic forms when used in therapy. Administered externally it can be applied directly by means of pomades, emulsions, poultices, and liniments. Alternatively it can be ingested in liquid form (drops, syrups and elixirs) or administered in solid forms (capsules). Recently the pharmaceutical industry has developed new ways of administering essential oils to facilitate their dosage and handling. These new ways come in the form of buffered microcapsules and consist of powder impregnated with essential oil (40 per cent). The fact that they are buffered gives them greater gastric tolerance. The essential oil of thyme can be administrated rectally in the form of suppositories and microenemas; vaginally, in the form of ovules; in sublingual administration in the form of solutions and nasally, in the form of drops and pomades. Finally we must not forget the inhalers and aerosols which are commonly used for the treatment of respiratory conditions.
Thyme oils (from e.g. Thymus vulgaris, Thymus serpyllum), especially thymol and carvacrol, provide an antiseptic action when eliminated via the lungs, but also has a mild irritant effect which stimulates the secretory cells of the mucosa and increases the movement of the ciliated epithelium in the bronchial tree (bronchi). This produces an increase of secretions which causes the decongestion of the entire respiratory system. The spasmolytic properties which these essential oils possess, capable of relaxing smooth bronchial muscle, determine their usefulness in the treatment of respiratory tract obstructive processes, and along with its expectorant properties make them effective against different types of coughs: cough caused by thick and viscous secretions, irritable cough, spasmodic cough.
Thyme in aromatherapy
A pleasant odour has always been, and still is, an important factor for people to feel good, and feeling well is synonymous with good health. The most ancient way to treat a patient in the sense of aromatherapy was the fumigation which was practised in all ancient civilisations. Although this was done by religious worship, it was nevertheless useful in the treatment of patients because the air became disinfected and the good aroma induced calmness. Up to the nineteenth century, the disinfectant effect of fumes was often used and people tried to banish the bad air in sick rooms by igniting good smelling candles and the doctors tried to protect themselves against infections by sniffing essential oils.
The term aromatherapy was coined in the late 1920s by the French cosmetic chemist R.M. Gattefosse, who noticed the excellent antiseptic properties and skin permeability of essential oils. Anticipating the trends of the 1980s, “New Age” and esoterics, Tisserand revived this term by including it in a general natural healing method with elements of wholistic, cosmic, anthroposophic and other phenomena. Confusingly, aromatherapy is used whenever good smelling plants or drugs are used to cure diseases not asking if the “aroma” is really responsible for the effect and additionally it is often combined with mystic elements.
A scientific clarification was necessary and it is due to Buchbauer that nowadays aromatherapy has become a scientific discipline. It is strictly based on his definition given as follows: “Aromatherapy: therapeutic uses of fragrances or at least mere volatiles to cure and to mitigate or prevent diseases, infections and indispositions only by means of inhalation”. To avoid misunderstandings here “aromatherapy” is used according to Buchbauer’s definition, although we are aware of the fact that in popular works “aromatherapy” is more often used in the traditional definition.
Concerning the application of thyme, a big overlap of aromatherapy with phytotherapy is inevitable, because the essential oil (the “aroma”) is the most important and effective principle of the herbal drug in both cures. Essential oils of thyme hold a privileged position because they have been demonstrated to have various pharmacological activities, the antimicrobial and spasmolytic ones being the most utilised in therapy. The essential oil of thyme, whichever administration route (orally, rectally or cutaneously) is chosen, is eliminated via the lungs and there it develops its capacity to act on the respiratory system.
Thyme in homoeopathy
Homoeopathy is based on an independent principle of therapy which was founded by the German doctor Samuel Hahnemann (1755—1843) who was teaching in Leipzig. This principle can be understood as a therapy which targets the internal regulation (stimulation) of the human body itself by a (special) drug whose reactivity corresponds to each patient individually. The methodical concepts base on the so-called “Ahnlichkeitsregel”, the Simile principle — Similia similibus curentur, meaning that “similar can be cured by something similar”, not as a law of nature but as an instruction for behaving. The feature of the remedy must be similar to the feature of the illness concerning location, form and character. Typically the drugs are administered in diluted forms which in Hahnemann’s idea corresponds to an increase in “potency”.
In homoeopathy numerous plants and parts of plants have a use for a multitude of indications. In order to preserve the homoeopathic remedies it became necessary, like in phytotherapy, to teview the knowledge on their effects. This was performed by a group of experts in Germany (Commission D). The fresh aerial parts of Thyme of two species, Thymus vulgaris and Thymus serpyllum, have traditionally been used in homoeopathy and both plants are described in the German homoeopathic pharmacopoeia (Homoeopathisches Arzneibuch, HAB 2000). The critical evaluation of published data in 1989 resulted in the decision that both plants lack any substantial effectiveness in homoeopathy (negative monographs). That means that the application of thyme in homoeopathy can no longer be recommended.
Pharmacokinetics of Thymol and Carvacrol
Data about the pharmacokinetics of essential oils are scarcely available, but there can be found a few on the phenolic terpenes, thymol and carvacrol. In an early publication Schroder and Vollmer (1932) described thymol and carvacrol to redistribute rapidly to the blood and kidneys following oral administration. These observations were made in experiments with animals.
The metabolism of carvacrol and thymol has been studied in rats. It was found that the urinary excretion of metabolites was rapid and only very small amounts were excreted after 24 h. Although large quantities of carvacrol and, especially, thymol were excreted unchanged (or as their glucuronide and sulphate conjugates), extensive oxidation of the methyl and isopropyl groups also occurred. This resulted in the formation of derivatives of benzyl alcohol and 2-phenylpropanol and their corresponding carboxylic acids. In contrast, ring hydroxylation of the two phenols was a minor reaction.
Takada investigated the metabolism of thymol in rabbits and humans. Thymol glucuronide featuring an intact aglycone was isolated from the urine of thymol-medicated rabbits and identified as an acetyl derivative of methyl glucuronate. The hydroxylated product of thymol, thymohydroquinone, was detected in small amounts in the urines of thymol-medicated humans. It was presumed that thymolhydroquinone is excreted as an ethereal sulfuric acid conjugate.
Toxicology of Thyme Oil
Toxic effects of the vegetable parts of thyme, Thymus vulgaris, have not been published, but it is important to mention that a certain level of toxicity can be found in the essential oil of thyme (acute oral LD50 = 4.7g/Kg rat). This toxicity has been attributed by some authors to thymol and carvacrol, their acute oral LD50 being 0.88-1.8g/Kg and 0.1— 0.18g/Kg, respectively. Furthermore, these phenols cause skin irritations and especially irritations of the mucosa, which precludes patients with gastroduodenal ulcers from the use of the essential oil. Thus undiluted thyme oil was found to be severely irritating to both mouse and rabbit skin, however it produced no irritation on human subjects when tested at 12 per cent. Hypersensitivity reactions have also been reported for this essential oil (); therefore it is strongly recommended to perform a tolerance test prior to attempting internal administration.
Various essential oils from Thymus contain considerable quantities of camphor and other terpenic ketones, which are known to produce convulsions and epileptic/neurotoxic crises. Limonene, which is a common component of thyme oil, is capable of diminishing the incidence of tumors in experimental animals treated with tumor-inducing agents. However upon oxidation of the molecule the risk of carcinogenesis is increased and it behaves as a catalysing agent. Therefore it is important to use fresh, non-oxidized essential oil of thyme in phytotherapy and aromatherapy.
Due to the toxic effects the use of the essential oil during pregnancy and lactation is contraindicated.
Selections from the book: “Thyme. The genus Thymus”. Edited by Elisabeth Stahl-Biskup. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 2002.