Licorice is a popular traditional Chinese medicine (TCM) used for the treatment of respiratory diseases including cough, sore throat, asthma, and bronchitis.4 It is derived from three plant species, Glycyrrhiza uralensis, G. glabra, and G. inflata. Many licorice-derived TCM patent drugs including Compound Licorice Tablets and Compound Licorice Oral Solutions are widely used as antitussives and expectorants in clinical practice.5 Literatures have reported the antitussive effects of 50% methanol extract of G. uralensis and the water extract of G. glabra in capsaicin- and citric acid-induced cough model in guinea pigs.6, 7, 8 Moreover, the antitussive activities of only three single compounds, namely liquiritin apioside, liquiritigenin, and liquiritin have been studied.9