大黄（四两酒洗） 浓朴（半斤炙去皮） 枳实（五枚炙） 芒硝（三合）
上四味。以水一斗。先煮二物。取五升。去滓。内大黄。煮取二升。去滓。内芒硝。更上火。微一两沸。分温再服。
得下余勿服。
成氏明理论云。承。顺也。伤寒邪气入胃者。谓之入府。府之为言聚也。胃为水谷之海。营卫之源。水谷会聚于胃。
变化而为营卫。邪气入于胃也。胃气郁滞。糟粕秘结。壅而为实。是正气不得舒顺也。本草曰。通可去滞。泄可去闭。
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。王冰曰。宣下必以苦。宜补必
以酸。言酸收而苦泄也。枳实味苦寒。溃坚破结。苦寒为主。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。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。故以芒硝为佐。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。以荡涤其燥热。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。如非大满。犹生寒热则病不除。况无满实者。而结胸痞气之属。由是而生矣。是
以脉经有云。伤寒有承气之戒。古人亦特谨之。
王海藏云。浓朴去痞。枳实泄满。芒硝软坚。大黄泄实。必痞满燥实四证全者。方可用之。
内台方议云。中满者泻之于内。此方通泻之剂也。伤寒之邪。自表传里。若至阳明。则为内实之盛也。如谵言。有
燥屎。大热便秘。腹满不得通。烦热。脉沉实。阳明汗多。少阴口燥。厥阴囊缩。非此大下泄之剂。不能已也。轻者。
小承气汤。重者。大承气汤。小承气。少浓朴。而无芒硝。以芒硝性寒。而能润坚。浓朴能破大实。病未至盛。以此减
之。大承气多浓朴而加芒硝。以其病之盛而大满大实。非此不能除也。仲景所用大承气者。二十五证。虽曰各异。然即
下泄之法也。其法虽多。不出大满大实大热。其脉沉实滑者之所当用也。
或问大承气汤。乃阳邪入府。大实痞满且坚者。方可用之。今内台方议云。少阴口燥。厥阴囊缩。非此大下泄之剂。
不能已。何也。余答云。仲景法。三阴热证。总系胃府邪实。阴经近里。府实则经壅热。所以热伤太阴。则嗌干腹满。
伤少阴。则口燥咽干。伤厥阴。则烦满囊缩。此为入府可下。均宜用大承气汤主之也。
大黄（四两，用酒清洗） 浓朴（半斤，炙烤后去皮） 枳实（五枚，炙烤） 芒硝（三合）
以上四味药。用水一斗。先煮前两种药（浓朴、枳实）。取药液五升。滤去药渣。加入大黄。再煮取二升药液。滤去药渣。加入芒硝。再次放在火上。微沸一两滚即可。分两次温服。
服药后若已通便，剩余的药不要服用。
成无己在《明理论》中说：承，意为顺从。伤寒邪气侵入胃腑的，称为入府。府的含义是聚积。胃是水谷汇聚的大海，也是营卫生成的源头。水谷会聚于胃，变化生成营卫。邪气进入胃中，导致胃气郁滞，糟粕秘结，壅塞而成实证，这是正气不能舒展顺畅。本草记载：通利可以去除停滞，泄下可以去除闭塞。如果堵塞而不通利，闭阻而不得通畅，就用汤剂荡涤，使堵塞者变得通利，闭阻者变得通畅，正气得以舒展顺畅，所以命名为“承气”。王冰说：宣通泻下必须用苦味药，适宜补益必须用酸味药，意思是酸味能收敛，苦味能泄降。枳实味苦性寒，能溃散坚结，以苦寒为主药，所以枳实为君药。浓朴味苦性温，《内经》说：燥邪内盛，用苦温之法治疗，能泄满除燥，以苦温为辅药，所以浓朴为臣药。芒硝味咸性寒，《内经》说：热邪内盛，用咸寒之法治疗。人受寒邪侵袭，就会变成热病。热气聚集在胃，就称为实证。咸寒的药物，用来消除热实，所以芒硝为佐药。大黄味苦性寒，《内经》说：燥邪胜复，用苦味药攻下。热气内盛，津液消耗而肠胃干燥，苦寒的药物，用来荡涤其燥热，所以大黄为使药。因此大黄有“将军”的称号。承气汤是泻下药，使用尤其应当审慎。确认有大满、大实、坚硬的燥屎，才可以投用。如果不是大满，仍有寒热，则病不能除去，何况没有满实的，反而会产生结胸、痞气等病症。因此《脉经》有云：伤寒有使用承气汤的禁忌，古人对此特别谨慎。
王海藏说：浓朴去除痞证，枳实泄除满证，芒硝软化坚结，大黄泄除实证。必须痞、满、燥、实四证俱全，才可以使用此方。
《内台方议》说：中焦满闷的，从内部泻除，此方是通泻的药剂。伤寒邪气，从体表传入体内，如果传到阳明经，就成为内实严重的病证。如谵语，有燥屎，大热便秘，腹部胀满不通，烦热，脉沉实，阳明汗多，少阴口燥，厥阴囊缩，不用这种大泻下的药剂，病不能痊愈。轻症用小承气汤，重症用大承气汤。小承气汤，减少浓朴用量，且没有芒硝，因为芒硝性寒，能润软坚结；浓朴能破除大实，病情未到严重程度，因此减去这些。大承气汤增加浓朴并加入芒硝，因为病情严重，大满大实，不用此方不能消除。张仲景所用大承气汤的情况，共有二十五证，虽然各不相同，但都是下泄的方法。其方法虽多，不出乎大满、大实、大热，脉象沉实滑者所应当使用的范围。
有人问大承气汤，乃是阳邪入府，大实痞满且坚硬的情况下，才可以使用。现在《内台方议》说：少阴口燥，厥阴囊缩，不用这种大泻下的药剂，病不能痊愈。为什么呢？我回答说：张仲景的法度，三阴经的热证，总归属于胃腑邪气实证。阴经靠近体内，腑实则经络壅滞发热，所以热伤太阴，则咽喉干、腹部胀满；伤少阴，则口燥咽干；伤厥阴，则烦闷囊缩。这属于入府可下的情况，都适宜用大承气汤主治。
Rhubarb (4 liang, washed with wine) Magnolia Bark (8 liang, roasted and skin removed) Immature Bitter Orange (5 pieces, roasted) Mirabilite (3 he)
The above four ingredients. Use one dou of water. First decoct the first two ingredients (Magnolia Bark and Immature Bitter Orange). Obtain five sheng of liquid. Strain to remove dregs. Add Rhubarb. Decoct to obtain two sheng of liquid. Strain to remove dargs. Add Mirabilite. Apply heat again until it boils slightly for one or two rolls. Divide into two doses and take warm.
If bowel movement is achieved, do not consume the remaining medicine.
Cheng Wuji stated in "Ming Lun": "Cheng" means to follow or obey. When pathogenic factors of Shanghan enter the stomach fu-organ, it is called entering the fu. The term "fu" implies gathering. The stomach is the sea of water and grain, and the source of Ying and Wei. Water and grain gather in the stomach, transforming into Ying and Wei. When pathogenic factors enter the stomach, Stomach Qi becomes stagnant, feces become constipated, causing obstruction and excess syndrome, preventing the righteous Qi from flowing smoothly. Materia Medica states: Unblocking can remove stagnation; purging can remove closure. If there is blockage without unblocking, or closure without patency, use a decoction to purge, making the blocked patent and the closed open, allowing the righteous Qi to flow smoothly. Hence the name "Cheng Qi". Wang Bing said: To promote purgation, bitter substances must be used; for appropriate tonification, sour substances must be used, meaning sour astringes and bitter drains. Immature Bitter Orange is bitter and cold, capable of dispersing hardness and breaking knots. As the primary bitter-cold agent, it serves as the Sovereign drug. Magnolia Bark is bitter and warm. The Neijing states: For internal dryness, treat with bitter-warm methods to drain fullness and remove dryness. As the auxiliary bitter-warm agent, it serves as the Minister drug. Mirabilite is salty and cold. The Neijing states: For internal heat, treat with salty-cold methods. Humans injured by cold develop heat diseases. Heat gathers in the stomach, constituting an excess condition. Salty-cold substances eliminate heat and excess, so Mirabilite serves as the Assistant drug. Rhubarb is bitter and cold. The Neijing states: For prevailing dryness, use bitter substances to purge. Internal heat excess consumes body fluids, causing dryness in the intestines and stomach. Bitter-cold substances purge this dryness-heat, so Rhubarb serves as the Envoy drug. Thus, Rhubarb bears the title "General". Cheng Qi Tang is a purgative formula; its use requires particular caution. It should only be administered when confirming major fullness, major excess, and hard dry stools. If it is not major fullness, chills and fever will persist, and the disease will not be cured. Moreover, if there is no fullness or excess, conditions like Jie Xiong (Chest Binding) and Pi Qi (Stagnant Qi) may arise. Therefore, the "Mai Jing" states: There are warnings against using Cheng Qi in Shanghan. Ancients were particularly cautious about this.
Wang Haizang said: Magnolia Bark removes Pi (stagnant fullness); Immature Bitter Orange drains Man (distension); Mirabilite softens Jian (hardness); Rhubarb drains Shi (excess). Only when all four syndromes—Pi, Man, Zao, and Shi—are present can this formula be used.
"Nei Tai Fang Yi" states: For middle-jiao fullness, purge from within. This formula is a general purgative agent. Pathogenic factors of Shanghan transmit from the exterior to the interior. Upon reaching the Yangming stage, it becomes severe internal excess. Symptoms include delirium, dry stools, high fever, constipation, abdominal distension with inability to pass gas or stool, irritability, deep and solid pulse, excessive sweating in Yangming, dry mouth in Shaoyin, and retracted scrotum in Jueyin. Without this strong purgative, the disease cannot cease. For mild cases, Xiao Cheng Qi Tang is used; for severe cases, Da Cheng Qi Tang is used. Xiao Cheng Qi Tang contains less Magnolia Bark and no Mirabilite, because Mirabilite is cold and moistens hardness, while Magnolia Bark breaks severe excess. If the disease is not severe, these are reduced. Da Cheng Qi Tang contains more Magnolia Bark and adds Mirabilite, because the disease is severe with major fullness and excess, which cannot be resolved otherwise. Zhang Zhongjing applied Da Cheng Qi Tang in twenty-five cases. Although varied, they all employ purgative methods. These methods, though numerous, fall under major fullness, major excess, and major heat, indicated by deep, solid, and slippery pulses.
One asked: Da Cheng Qi Tang is applicable only when yang pathogens enter the fu-organ, presenting with major excess, Pi, Man, and hardness. Yet "Nei Tai Fang Yi" states that for Shaoyin dry mouth and Jueyin retracted scrotum, this strong purgative is necessary. Why? I answer: According to Zhang Zhongjing's principles, heat syndromes of the three Yin meridians generally relate to excess pathogens in the stomach fu. Yin meridians are close to the interior; fu-excess causes meridian congestion and heat. Thus, heat injuring Taiyin causes throat dryness and abdominal fullness; injuring Shaoyin causes dry mouth and throat; injuring Jueyin causes irritability, fullness, and retracted scrotum. These constitute conditions where entering the fu allows for purgation, and Da Cheng Qi Tang is appropriate for all.