虚者补之。实者泻之。此言所共知。至如峻缓轻重之剂。则又临时消息焉。大满大
实。坚有燥屎。非峻剂则不能泄。大小承气汤峻。所以泄坚满者也。如不至大坚满
邪热甚。而须攻下者。又非承气汤之可投。必也轻缓之剂攻之。大柴胡汤缓。用以
逐邪热也。经曰。伤寒发热七八日。虽脉浮数者。可下之。宜大柴胡汤。又曰。太阳病
过经十余日。反二三下之。后四五日。柴胡证仍在者。先与小柴胡。呕不止。心下急。
郁郁微烦者。为未解也。可大柴胡下之则愈。是知大柴胡为下剂之缓也。柴胡味
苦平微寒。伤寒至于可下。则为热气有余。应火而归心。苦先入心。折热之剂。必以
苦为主。故以柴胡为君。黄芩味苦寒。王 曰。大热之气。寒以取之。推除邪热。必以
寒为助。故以黄芩为臣。芍药味酸苦微寒。枳实味苦寒。内经曰。酸苦涌泄为阴。泄
实折热。必以酸苦。故以枳实芍药为佐。半夏味辛温。生姜味辛温。大枣味甘温。辛
者散也。散逆气者。必以辛。甘者缓也。缓正气者。必以甘。故半夏生姜大枣为之使
也。一方加大黄。以大黄有将军之号。而功专于荡涤。不加大黄。恐难攻下。必应以
大黄为使也。用汤者。审而行之。则十全之功可得矣。
柴胡（君半斤） 黄芩（臣三两） 枳实（佐四枚炙） 芍药（佐三两）
生姜（使五两切） 半夏（使半升洗） 大枣（使十二枚擘）
上件七味。以水一斗二升。煮取六升。去渣再煎。温服一升。日三服。一方加大黄
二两。若不加。恐不名大柴胡汤。
虚证用补法，实证用泻法。这是人们所共知的道理。至于药性峻烈或缓和、分量轻重不同的方剂，则需要根据病情临时斟酌决定。如果腹部胀满严重且结实，体内有坚硬的燥屎，非用峻猛的药剂不能通泄。大小承气汤药性峻猛，是用来攻下坚硬积滞的。如果并未达到大坚满的程度，但邪热极盛，又必须采用攻下法治疗时，就不能投用承气汤，必须使用轻缓的药剂来攻逐。大柴胡汤药性缓和，用来驱逐邪热。《内经》说：伤寒发热七八天，虽然脉象浮数，也可以使用下法，适宜用大柴胡汤。又说：太阳病经过病程十余日，反而被误用了二三次攻下法，之后过了四五日，如果少阳柴胡证仍然存在，先给予小柴胡汤；如果呕吐不止，胃脘部拘急不适，心中郁郁不舒且微有烦闷，说明病邪未解，可以使用大柴胡汤攻下则痊愈。由此可知，大柴胡汤属于下法中较为缓和的方剂。
柴胡味苦、平、微寒。伤寒发展到可以使用下法的时候，说明热气有余，火气归于心经。苦味先入心，是折减热气的药物，必须以苦味为主，所以以柴胡为君药。黄芩味苦、寒。王冰说：对于大热之气，要用寒凉药来取效，推除邪热，必须以寒性药作为辅助，所以以黄芩为臣药。芍药味酸、苦、微寒。枳实味苦、寒。《内经》说：酸味和苦味具有涌吐和泄下的作用，属于阴。泄去实邪、折减热气，必须以酸苦味为主，所以以枳实、芍药为佐药。半夏味辛、温。生姜味辛、温。大枣味甘、温。辛味能发散，发散逆乱之气，必须以辛味为主。甘味能缓和，缓和正气（调和脾胃），必须以甘味为主，所以以半夏、生姜、大枣为使药。另一版本加入大黄，因为大黄有“将军”的称号，功效专于荡涤肠胃，如果不加大黄，恐怕难以起到攻下的作用，应当以大黃为使药。使用汤剂时，审慎地施行，就能获得十全的功效。
柴胡（君药，半斤） 黄芩（臣药，三两） 枳实（佐药，四枚，炙） 芍药（佐药，三两）
生姜（使药，五两，切） 半夏（使药，半升，洗） 大枣（使药，十二枚，掰开）
以上七味药，用水一斗二升，煮取六升药液，去掉药渣后再次煎煮。每次温服一升，每日服用三次。另一版本加大黄二两。如果不加大黄，恐怕就不叫大柴胡汤了。
Deficient patterns are treated with tonification; excess patterns are treated with purgation. This is a principle universally known. However, regarding preparations that are harsh or mild, heavy or light in dosage, one must exercise discretion according to the specific circumstances. If there is severe fullness and solidity, with hard dry stools retained in the intestines, only harsh purgatives can effect discharge. Da Cheng Qi Tang (Major Order the Qi Decoction) and Xiao Cheng Qi Tang (Minor Order the Qi Decoction) are harsh in nature, used to purge hard accumulations. If the condition does not reach the state of severe hardness and fullness, but the pathogenic heat is intense and purgation is required, then Cheng Qi Tangs should not be administered. Instead, mild and gentle preparations must be used to expel the pathogen. Da Chai Hu Tang (Major Bupleurum Decoction) is mild in action, employed to drive out pathogenic heat. The Classics state: "In cold damage with fever for seven or eight days, even if the pulse is floating and rapid, purgation may be applied; Da Chai Hu Tang is appropriate." It also states: "In Taiyang disease (Disease of the Taiyang Channel), after more than ten days, if it was mistakenly subjected to purgation two or three times, and after another four or five days, the Chai Hu syndrome (Bupleurum pattern) persists, first administer Xiao Chai Hu Tang (Minor Bupleurum Decoction). If vomiting continues unceasingly, there is urgency and distress in the epigastrium, and a slight sense of depression and vexation, the disease has not resolved. Da Chai Hu Tang may be used to purge, resulting in recovery." From this, we know that Da Chai Hu Tang is a mild purgative.
Chai Hu (Bupleuri Radix) is bitter, neutral, and slightly cold. When cold damage progresses to a stage where purgation is indicated, it signifies an excess of heat qi. Fire corresponds to the Heart. Bitter flavors enter the Heart first. Agents that reduce heat must primarily utilize bitter flavors; therefore, Chai Hu serves as the Sovereign (Jun) herb. Huang Qin (Scutellariae Radix) is bitter and cold. Wang Bing stated: "For extreme heat, cold agents are used to subdue it. To eliminate pathogenic heat, cold herbs must assist." Therefore, Huang Qin serves as the Minister (Chen) herb. Shao Yao (Paeoniae Radix Alba) is sour, bitter, and slightly cold. Zhi Shi (Aurantii Fructus Immaturus) is bitter and cold. The Inner Canon states: "Sour and bitter induce upward vomiting and downward purgation, belonging to Yin." To drain excess and reduce heat, sour and bitter flavors are essential; thus, Zhi Shi and Shao Yao serve as Assistant (Zuo) herbs. Ban Xia (Pinelliae Rhizoma) is acrid and warm. Sheng Jiang (Zingiberis Rhizoma Recens) is acrid and warm. Da Zao (Jujubae Fructus) is sweet and warm. Acrid flavors disperse; to scatter rebellious qi, acrid flavors are necessary. Sweet flavors moderate; to harmonize healthy qi, sweet flavors are necessary. Thus, Ban Xia, Sheng Jiang, and Da Zao serve as Envoy (Shi) herbs. Another version adds Da Huang (Rhei Radix et Rhizoma). Since Da Huang bears the title "General" and its function is specifically to scour and cleanse, without Da Huang, it would be difficult to achieve purgation. Therefore, Da Huang should be added as an Envoy herb. When using decoctions, careful application yields perfect results.
Chai Hu (Sovereign, 8 liang) Huang Qin (Minister, 3 liang) Zhi Shi (Assistant, 4 pieces, roasted) Shao Yao (Assistant, 3 liang)
Sheng Jiang (Envoy, 5 liang, sliced) Ban Xia (Envoy, 0.5 sheng, washed) Da Zao (Envoy, 12 pieces, split)
Take the above seven ingredients, add 12 sheng of water, boil to obtain 6 sheng of liquid. Remove the dregs and decoct again. Take 1 sheng warm, three times daily. Another version adds 2 liang of Da Huang. Without Da Huang, it arguably cannot be called Da Chai Hu Tang.