In order to explore the dose-response patterns of Gancao (Radix Glycyrrhizae) in Shanghan Lun (Treatise on Febrile Diseases), all prescriptions containing Gancao in Shanghan Lun were analyzed by frequency and hierarchical clustering analysis. The doses of Gancao used in Shanghan Lun ranged from six zhu (Chinese unit, and one zhu is equal to 0.65 g) to four liang (Chinese unit, and one liang is equal to 15.625 g). Doses of one, two, three or four liang were commonly used. One liang Gancao as juvantia was usually matched with Mahuang (Herba Ephedrae), Xingren (Semen Armeniacae) and Guizhi (Ramulus Cinnamomi) for restricting the excessive diaphoresis of Mahuang. Two liang Gancao was often matched with some couple drugs, such as Guizhi and Shaoyao (Radix Paeoniae), Shigao (Gypsum Fibrosum) and Zhimu (Rhizoma Anemarrhenae), Fuzi (Radix Aconiti Lateralis) and Ganjiang (Rhizoma Zingiberis), for warming yang to supplement qi, nourishing yin, detoxifying Fuzi, and preventing qi impairment from heat evil. Three liang Gancao was mainly matched with Banxia (Rhizoma Pinelliae) or Renshen (Radix Ginseng) for treating middle energizer emesis. Four liang Gancao was matched with Ganjiang or tonifying herbs for invigorating vital qi and relieving spasm in deficiency syndromes with contraction, palpitation or diarrhea. Gancao is used for treating many syndromes in Shanghan Lun. It is frequently used to treat excess or heat syndromes with one or two liang in a dose and deficiency or cold syndromes with three or four liang in a dose.

Key words: Shanghai Lun , Radix Glycyrrhizae, Compatibility, Dose-response relationship, Drug