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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.