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Cheng (to follow/adhere) means to comply or adapt. When pathogenic factors of Shanghan (Cold Damage) enter the stomach and fu organs, it is termed "entering the fu." The term "fu" implies gathering or accumulation. The stomach is the sea of water and grain, and the source of Ying (Nutritive Qi) and Wei (Defensive Qi). Water and grain gather in the stomach, undergo transformation, and become Ying and Wei. When pathogenic factors enter the stomach, qi stagnation occurs within the stomach, fecal matter becomes constipated, and obstruction leads to excess conditions. This prevents the healthy qi from flowing smoothly and freely. The Bencao states: "Unblocking methods remove stagnation; purgative methods eliminate pathogens." If there is blockage without flow, or closure without passage, decoctions are used to cleanse and wash away the impurities, making the blocked passages open and the closed ones patent, thereby allowing the healthy qi to flow smoothly. Hence, the name "Chengqi" (Adapting Qi) is given. Wang Bing stated: "Purgation requires bitter flavors; tonification requires sour flavors." This indicates that sour flavors have an astringent effect, while bitter flavors have a draining effect. Zhi Shi (Immature Bitter Orange) is bitter and cold; it breaks down hardness and shatters accumulations. Therefore, it serves as the Jun (Emperor) herb due to its bitter-cold nature. Hou Po (Magnolia Bark) is bitter and warm. The Neijing states: "For internal dryness hyperactivity, treat with bitter-warm methods." It drains fullness and removes dryness, so it serves as the Chen (Minister) herb due to its bitter-warm nature. Mang Xiao (Mirabilite) is salty and cold. The Neijing states: "For internal heat hyperactivity, treat with salty-cold methods." When humans are injured by cold, they develop heat diseases. Heat qi gathers in the stomach, constituting an "excess" condition. Salty-cold substances eliminate and dissipate heat-excess, so Mang Xiao serves as the Zuo (Assistant) herb. Da Huang (Rhubarb) is bitter and cold. The Neijing states: "When dryness prevails, use bitter substances to purge downward." Internal heat hyperactivity consumes body fluids, leading to dry intestines and stomach. Bitter-cold substances cleanse and wash away dryness-heat, so Da Huang serves as the Shi (Envoy) herb. Thus, Da Huang bears the title "General." Chengqi Tang belongs to the category of purgative formulas. Its use must be particularly cautious. It should only be administered when confirmed large-fullness, large-excess, hardness, and dry stool are present. If these conditions are not met, chills and fever may persist, and the disease will not be resolved. Moreover, improper use in cases lacking fullness and excess can lead to conditions such as Jie Xiong (Chest Binding) and Pi Qi (Pi Syndrome). Therefore, the Mai Jing states: "There are warnings regarding the use of Chengqi in Shanghan." Ancient physicians were especially prudent regarding this.

Zhi Shi (Jun, 5 pieces, roasted), Hou Po (Chen, 0.5 jin, roasted, peeled), Mang Xiao (Zuo, 3 he), Da Huang (Shi, 4 liang, washed with wine).

Take the above four herbs. Add one dou of water. First decoct Zhi Shi and Hou Po until five sheng of liquid remains. Strain out the dregs. Add Da Huang and decoct further until two sheng remain. Strain out the dregs. Add Mang Xiao and boil gently for one or two boils. Divide into two doses and take warm. If bowel movement occurs, do not consume the remaining medicine.