The European Commission has approved the administration of thyme for cough and bronchitis. In the case of thymol and carvacrol, a broad spectrum of effect against bacteria involved in the infections of the upper respiratory tract has been observed. It is believed that thymol and carvacrol exert their antibacterial activity through complex formation with the proteins in the bacterial membrane. A synergistic effect has also been demonstrated for thymol and carvacrol. Carvacrol is the main ingredient in essential oil of thyme; its antibacterial and antifungal activities have been demonstrated against various microorganisms. It has also been demonstrated that sufficient doses of thymol and carvacrol have relaxant effect on the trachea.
Essential oil of Iranian (Shirazi) thyme is effective against pathogenic bacteria, especially Staphylococcus aureus. Iranian (Shirazi) thyme has always been considered as effective in elimination of symptoms like cough and upper respiratory tract catarrh and also as an expectorant having antispasmodic effects. It has been used in adults for treatment of bronchitis and cough with spasm and in children for treatment of pertussis. Various clinical trials have demonstrated the effectiveness of thyme on productive coughs.
In a randomized double-blind clinical trial, 60 patients with productive cough were administered thyme syrup or bromhexine syrup for a period of 5 days. According to the patents’ self-reports, there existed no significant difference between the two groups and both observed identical improvement by both of the medications. There was significant non-statistical progress in health of non-smokers compared to smokers in both groups.
Furthermore, in a controlled randomized double-blind clinical trial, to study the antitussive effects of thyme and fennel, 119 patients with acute cough were administered, for three days three times a day 20 drops each time, either a drop containing essential oil of sweet fennel and Iranian thyme or clobutinol drop or placebo. At the end of this period, 50% were reported as cured in the groups receiving the drop containing sweet fennel and Iranian thyme essential oil and clobutinol drop; the percentage was 9.1% in the placebo group. The efficacy of the drop containing sweet fennel and Iranian thyme essential oil, clobutinol drop and placebo was reported 66.7%, 55% and 14.3% in patients with productive coughs, and 56.5%, 55% and 20% in patients with dry coughs, respectively. A significant difference was observed in the healing rate of cough between the drop containing sweet fennel and Iranian thyme essential oil, clobutinol drop and the placebo (p<0.01), but there was no significant difference between the drop containing sweet fennel and Iranian thyme essential oil and clobutinol drop (p>0.4).
Marshmallow leaves have been approved by E Commission for treatment of irritations of oral and pharyngeal mucous concomitant with dry coughs. Also, marshmallow is used in treatment of inflammations of the respiratory and digestive system, reflex coughs and bronchitis. The antitussive effects of the total extract and polysaccharides of marshmallow root has been compared with non-opioid antitussive agents in animal studies. Based on the results, administration of the polysaccharides results in statistically significant reduction in the number of coughs and inhibition of cough reflex; the efficacy of the total extract has been less than polysaccharides.
In in vitro and in vivo conditions, the rhamnogalacturonan isolated from marshmallow root has demonstrated various biological effects upon the cough reflex and the reactivity of the smooth muscles of respiratory tract induced by citric acid. This phytoconstituent has dose-dependent antitussive effects, comparable with codeine (opioid agonist). Nonetheless, the reactivity of the airway smooth muscles is not significantly affected by rhamnogalacturonan in in vitro and in vivo conditions. Therefore, bronchodilator properties are not involved in its cough suppressant effects. Furthermore, activation of K+ATP ion canals has had no effect in the antitussive mechanism. It seems that the cough suppressant effects of the rhamnogalacturonan isolated from marshmallow root is related to the functions of 5-HT2 serotonergic receptors.
Iranian Thyme and Marshmallow
In a randomized double-blind clinical trial, 157 patients aged 10-85, suffering acute cough were administered 5 ml Bronchobarij syrup (78 patients) or dextromethorphan syrup (79 patients), every 8 hours, for 4 days. Twenty four, 48 and 96 hours after the commencement of the treatment, clinical symptoms were registered using questionnaires. In each case, the degree of healing was evaluated as complete response (complete eradication of cough), partial response (satisfaction of the patient from the decrease in cough or a reduction in length of cough to half) or no response (no change in the severity of cough). Also, the severity of cough was evaluated in each session using Visual Analogue Scale (VAS): a 0-10 scale was presented, in which 0 was described as no cough and 10 as debilitating cough.
According to the results of this study, after 96 hours, 50% of the patients who were administered the syrup containing Iranian thyme and marshmallow extract were fully cured. In the dextromethorphan group this percentage was 49.3%, and no significant relation was seen between the type of medication and the degree of response (p=0.94). At the beginning of the test, the average VAS score was 6.7 in the Iranian thyme and marshmallow extract syrup group and 6.8 in the dextromethorphan group. At the 24, 48 and 96 hour intervals after the beginning of the test, this score was 4.4, 3.3 and 2.67 in the Iranian thyme and marshmallow extract syrup and 4.49, 3.35 and 2.4, respectively. In case of both medications, significant efficacy was observed throughout the course of the treatment (p<0.001). Also, the average reduction in the VAS score at different intervals was 2.3, 3.26 and 3.85 in patients using Iranian thyme and marshmallow extract syrup and 2.3, 3.4 and 4.1 in the dextromethorphan group, respectively. However, no significant difference was observed between the two drugs in treatment of cough (p>0.06).