承顺也。伤寒邪气入胃者。谓之入腑。腑之为言聚也。胃为水谷之海。荣卫之源。水
谷会聚于胃。变化而为荣卫。邪气入于胃也。胃中气郁滞。糟粕秘结。壅而为实。是
正气不得舒顺也。本草曰。通可去滞。泄可去邪。塞而不利。闭而不通。以汤荡涤。使
塞者利而闭者通。正气得以舒顺。是以承气名之。王 曰。宜下必以苦。宜补必以
酸。言酸收而苦泄也。枳实苦寒。溃坚破结。则以苦寒为之主。是以枳实为君。浓朴
味苦温。内经曰。燥淫于内。治以苦温。泄满除燥。则以苦温为辅。是以浓朴为臣。芒
硝味咸寒。内经曰。热淫于内。治以咸寒。人伤于寒。则为病热。热气聚于胃。则谓之
实。咸寒之物。以除消热实。故芒硝为佐。大黄味苦寒。内经曰。燥淫所胜。以苦下之。
热气内胜。则津液消而肠胃燥。苦寒之物。以荡涤燥热。故以大黄为使。是以大黄
有将军之号也。承气汤下药也。用之尤宜审焉。审知大满大实。坚有燥屎。乃可投
之也。如非大满。则犹生寒热。而病不除。况无满实者。而结胸痞气之属。由是而生
矣。是以脉经有曰。伤寒有承气之戒。古人亦特谨之。
枳实（君五枚炙） 浓朴（臣半斤炙去皮） 芒硝（佐三合） 大黄（使四两酒洗）
上四味。以水一斗。先煮二物。取五升。去渣。内大黄。更煮取二升。去渣内芒硝。更上微火一两沸。分温再服。
得下余勿服。
承，意为顺从、顺应。伤寒邪气侵入胃腑的，称为“入腑”。所谓“腑”，其含义是汇聚。胃是水谷汇聚的海洋，也是营卫之气生成的源头。水谷在胃中汇聚，经过变化转化为营卫之气。当邪气进入胃中时，会导致胃中气机郁滞，糟粕秘结不通，壅塞而形成实证。这使得正气无法舒展顺畅。《本草》记载：“通利的方法可以去除停滞，泄下的方法可以祛除邪气。”如果堵塞而不通畅，闭塞而不得通行，就用汤剂来荡涤肠胃，使堵塞者变得通利，闭塞者得以畅通，从而使正气能够舒展顺畅。因此，将此方命名为“承气”（顺应正气）。王冰说：“适宜用下法的必须用苦味药，适宜用补益的必须用酸味药。”这是说明酸味具有收敛作用，苦味具有泄降作用。枳实（Zhi Shi, Immature Bitter Orange）味苦性寒，能溃散坚积、破除结聚，所以以苦寒之性的枳实作为君药。厚朴（Hou Po, Magnolia Bark）味苦性温，《内经》说：“燥邪内盛，应用苦温之法治疗。”用以泄除胀满、消除燥结，所以以苦温之性的厚朴作为臣药。芒硝（Mang Xiao, Mirabilite）味咸性寒，《内经》说：“热邪内盛，应用咸寒之法治疗。”人受寒邪侵袭，就会化热生病。热气聚集在胃中，就称为“实”。咸寒性质的药物，用来清除消散热实，所以芒硝作为佐药。大黄（Da Huang, Rhubarb）味苦性寒，《内经》说：“燥邪胜复，应用苦味药以下夺。”热气在内亢盛，就会导致津液消耗，肠胃干燥。苦寒性质的药物，用来荡涤燥热，所以大黄作为使药。因此，大黄有“将军”的称号。承气汤属于泻下药。使用它尤其应当审慎。只有确认是大满大实、坚硬且有燥屎的情况，才可以投用此方。如果不是大满大实，那么仍然会产生寒热症状，且疾病不能解除。更何况对于没有满实症状的患者，如果使用不当，会导致结胸、痞气等病症产生。因此，《脉经》中说：“伤寒病有使用承气汤的禁忌。”古人对此也特别谨慎。
枳实（君药，五枚，炙） 厚朴（臣药，半斤，炙，去皮） 芒硝（佐药，三合） 大黄（使药，四两，酒洗）
以上四味药，用水一斗，先煮枳实和厚朴两味药，取汁五升，去渣。加入大黄，再煮取汁二升，去渣。加入芒硝，再上火微沸一两滚。分两次温服。如果已经通便，剩下的药不要服用。
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.