The listings of research below represents a compilation of scientific articles found on the topic, with a very brief overview description of each article/study. This compilation of research articles does not necessarily imply that there are adequate results to demonstrate safe and/or effective human use of any herb listed.
Cineole demonstrated good expectorant activity in patients in an emergency room. Li, G. A. O. (1989). The expectorant effect of cineole compositus in 386 patients with respiratory diseases. 6, 015
In a randomized double blind placebo controlled study of 152 patients, 100 mg of cineole three times a day reduced symptoms of accute sinusitis. From: Kehrl, W., Sonnemann, U., & Dethlefsen, U. (2004). Therapy for Acute Nonpurulent Rhinosinusitis With Cineole: Results of a Double‐Blind, Randomized, Placebo‐Controlled Trial. The Laryngoscope, 114(4), 738-742.
A review of 1,234 children ages 2-17 had reduced bronchial symptoms with age appropriate doses of a syrup containing thyme and ivy. From: Marzian, O. (2007). Treatment of acute bronchitis in children and adolescents. Non-interventional postmarketing surveillance study confirms the benefit and safety of a syrup made of extracts from thyme and ivy leaves. MMW Fortschritte der Medizin, 149(27-28 Suppl), 69-74.
In a double-blind, randomized, placebo-controlled, multicenter, study with 150 patients, an extract with thyme and primrose was effective and tolerable in treating acute bronchitis. The author did a similar study with 189 patients a year later, with a similar outcome. From: Gruenwald, J., Graubaum, H. J., & Busch, R. (2005). Efficacy and tolerability of a fixed combination of thyme and primrose root in patients with acute bronchitis. Arzneimittelforschung, 55(11), 669-676.
The herbal brand Bronchipret containing thyme extract was just as effective in treating bronchial symptoms as synthetic drugs in a matched-pair comparison study of 7783 patients. From: Ernst, E., März, R., & Sieder, C. (1997). A controlled multi-centre study of herbal versus synthetic secretolytic drugs for acute bronchitis. Phytomedicine, 4(4), 287-293.
In a double blind, randomized, clinical trial of 52 pediatric patients, a cough syrup containing a thyme like plant reduced cough safely in young children. From: Hosseini, F., Mahjoub, H., Amanati, A., Fazlian, M. M., & Sedighi, I. (2016). Comparison of Zataria multiflora Extract Syrup and Diphenhydramine in the Treatment of Common Cold-Induced Cough in Children: A Double-Blind, Randomized, Clinical Trial. Archives of Pediatric Infectious Diseases, 4(3).
A combination of pinene, limonene, and cineole improved mucociliary clearance. From: Dorow, P., Weiss, T. H., Felix, R., & Schmutzler, H. (1987). [Effect of a secretolytic and a combination of pinene, limonene and cineole on mucociliary clearance in patients with chronic obstructive pulmonary disease]. Arzneimittel-Forschung, 37(12), 1378-1381.
1,8-cineol controlled airway mucus hypersecretion by cytokine inhibition, and may be a useful treatment to reduce symptoms of asthma, sinusitis and COPD. From: Juergens, U. R., Engelen, T., Racké, K., Stöber, M., Gillissen, A., & Vetter, H. (2004). Inhibitory activity of 1, 8-cineol (eucalyptol) on cytokine production in cultured human lymphocytes and monocytes. Pulmonary Pharmacology & Therapeutics, 17(5), 281-287.
Listed are herbs commonly used for cough suppression.These herbs include: Acacia catechu, Acorus calamus, Adhatoda vasica, Allium sativum, Angelica archangelica, Astragalus membranaceus, Carum copticum, Lavandula angustifolia, Lobelia inflata, Salvia officinalis, Sambucus nigra, Tussilago farfara, Valeriana officinalis, Verbascum thapsus, and Zingiber officinale. From: Sultana, S., Khan, A., & Alhazmi, M. M. S. H. A. (2016). Cough Suppressant Herbal Drugs: A Review. International Journal of Pharmaceutical Science Invention, 5(5), 15-28.
Lemon oil had an expectorant action in rabbits, limonene and pinene were active components. From: Sheppard, E. P., & Boyd, E. M. (1970). Lemon oil as an expectorant inhalant. Pharmacological Research Communications, 2(1), 1-16.
In a study of 105 children ages 2-18 years with nighttime cough, parents rated honey favorably in reducing the cough associated with respiratory infections. From: Paul, I. M., Beiler, J., McMonagle, A., Shaffer, M. L., Duda, L., & Berlin, C. M. (2007). Effect of honey, dextromethorphan, and no treatment on nocturnal cough and sleep quality for coughing children and their parents. Archives of pediatrics & adolescent medicine, 161(12), 1140-1146.
In a double blind study of 300 children ages 1-5 years, the three different types of honey tested reduced nocturnal coughing. From: Cohen, H. A., Rozen, J., Kristal, H., Laks, Y., Berkovitch, M., Uziel, Y., … & Efrat, H. (2012). Effect of honey on nocturnal cough and sleep quality: a double-blind, randomized, placebo-controlled study. Pediatrics, 130(3), 465-471.
An in vitro study showed topical application of eucalyptus oil could reduce bacteria-induced mucus hypersecretion. From: Sudhoff, H., Klenke, C., Greiner, J. F., Müller, J., Brotzmann, V., Ebmeyer, J., … & Kaltschmidt, C. (2015). 1, 8-Cineol reduces mucus-production in a novel human ex vivo model of late rhinosinusitis. PloS one, 10(7), e0133040.
A fructofuranan of burdock root was antitussive in cats. From: Kardošová, A., Ebringerova, A., Alföldi, J., Nosál’ová, G., Fraňová, S., & Hřı́balová, V. (2003). A biologically active fructan from the roots of Arctium lappa L., var. Herkules. International journal of biological macromolecules, 33(1), 135-140.
Ginger constituents may help relax smooth muscles of the throat related to asthma complaints. From: Townsend, E. A., Siviski, M. E., Zhang, Y., Xu, C., Hoonjan, B., & Emala, C. W. (2013). Effects of ginger and its constituents on airway smooth muscle relaxation and calcium regulation. American journal of respiratory cell and molecular biology, 48(2), 157-163.
Glycyrrhiza glabra (licorice root) and Adhatoda vasica had an antitussive activity in mice comparable to that of codeine sulphate. From: Jahan, Y., & Siddiqui, H. H. (2012). Study of antitussive potential of Glycyrrhiza glabra and Adhatoda vasica using a cough model induced by sulphur dioxide gas in mice. International journal of Pharmaceutical Sciences and research, 3(6), 1668.
Glycyrrhiza glabra induced cough efforts in guinea pigs more effectively than codeine. From: Saha, S., Nosál’ová, G., Ghosh, D., Flešková, D., Capek, P., & Ray, B. (2011). Structural features and in vivo antitussive activity of the water extracted polymer from Glycyrrhiza glabra. International journal of biological macromolecules, 48(4), 634-638.
In a double blind study, A. officinalis reduced the cough of those taking and having side effects from enzyme inhibitor drugs to treat hypertension. Rouhi, H., & Ganji, F. (2007). Effect of Althaea officinalis on cough associated with ACE inhibitors. Pakistan Journal of Nutrition, 6(3), 256-258.
In vitro, marshmallow extracts stimulated epithelial cells to support the traditional use for treatment of irritated mucous membranes. From: Deters, A., Zippel, J., Hellenbrand, N., Pappai, D., Possemeyer, C., & Hensel, A. (2010). Aqueous extracts and polysaccharides from Marshmallow roots (Althea officinalis L.): Cellular internalisation and stimulation of cell physiology of human epithelial cells in vitro. Journal of ethnopharmacology, 127(1), 62-69.
Lozenges containing marshmallow root showed an effect in treating irritated oropharyngeal mucosa associated with a dry irritable cough. Benbassat, N., Kostova, B., Nikolova, I., & Rachev, D. (2013). Development and evaluation of novel lozenges containing marshmallow root extract. Pak J Pharm Sci, 26, 1103-1107.
In an open trial of 62 patients, a cough syrup made from ivy leaves, thyme herb, aniseed and marshmallow root was effective. From: Büechi, S., Vögelin, R., von Eiff, M. M., Ramos, M., & Melzer, J. (2005). Open trial to assess aspects of safety and efficacy of a combined herbal cough syrup with ivy and thyme. Complementary Medicine Research, 12(6), 328-332.
Fennel seed was used to treat cough. From: Subhash, A. C. (1999). Controlling angiotensin-converting-enzyme-inhibitor induced cough by fennel fruit. Indian Journal of Pharmacology, 31(2), 159.
In this placebo-controlled, double-blind, randomized trial 246 patients with chronic bronchitis, long use (1 month) of myrtol (contains alpha pinene) over one month was tolerable and effective. From:Meister, R., Wittig, T., Beuscher, N., & de Mey, C. (1999). Efficacy and tolerability of Myrtol standardized in long-term treatment of chronic bronchitis. Arzneimittelforschung, 49(04), 351-358.
In this 2 week treatment of 676 patients with chronic bronchitis, myrtol (contains alpha pinene, cineole, and d-limonene) was safe and effective. From:Matthys, H., de Mey, C., Carls, C., Ryś, A., Geib, A., & Wittig, T. (2000). Efficacy and tolerability of myrtol standardized in acute bronchitis. Arzneimittelforschung, 50(08), 700-711.
In vivo studies attributed the antitussive effect of coltsfoot to the following constituents: chlorogenic acid, 3,5-dicaffeoylquinic acid, and rutin. From: Li, Z. Y., Zhi, H. J., Zhang, F. S., Sun, H. F., Zhang, L. Z., Jia, J. P., … & Qin, X. M. (2013). Metabolomic profiling of the antitussive and expectorant plant Tussilago farfara L. by nuclear magnetic resonance spectroscopy and multivariate data analysis. Journal of pharmaceutical and biomedical analysis, 75, 158-164.
Flower buds from coltsfoot had an antitussive and expectorant effect on mice. From: Li, Z. Y., Zhi, H. J., Xue, S. Y., Sun, H. F., Zhang, F. S., Jia, J. P., … & Qin, X. M. (2012). Metabolomic profiling of the flower bud and rachis of Tussilago farfara with antitussive and expectorant effects on mice. Journal of ethnopharmacology, 140(1), 83-90.
Extract from the leaves of Passiflora incarnata reduced cough activity in induced mice. From: Dhawan, K., & Sharma, A. (2002). Antitussive activity of the methanol extract of Passiflora incarnata leaves. Fitoterapia, 73(5), 397-399.