In addition, the frequency of the herbs used in the herbal formulae recommended by the Chinese guidelines for every stage and in total were computed (Fig. 1 ). The results showed that these formulae contain 12 herbs with a frequency of use 30 or more times in the treatment formulae in all stages. Both Armeniacae Semen Amarum and Ephedrae Herba were found to be the top 10 herbs with the highest frequency of use in the mild, moderate and severe stages. The Gypsum Fibrosum and Lepidii seu Descurainiae Semen were also the top 10 most common herbs used in the moderate and severe stages. In addition, Agastachis Herba, Forsythiae Fructus, Atractylodis Rhizoma, and Scutellariae Radix were also highly used in both the mild and moderate stages. Notably, Glycyrrhizae Radix et Rhizoma was found in the top 10 herbs with the highest usage frequency in all four stages. It was also the herb with the highest frequency of usage in total.
Fig. 1 Frequency of commonly used herbs in the herbal formulae for treating patients with COVID-19 in (A) mild stage; (B) moderate stage; (C) severe stage; (D) recovery stage; (E) all stages.