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Dahuang (Rhei Radix et Rhizoma) strongly clears damp-heat from the Blood level and purges有形 (solid) accumulations and stagnation within.

It is extremely bitter and extremely cold. It enters the Foot-Taiyin Spleen channel, as well as the Hand-Yangming Large Intestine, Foot-Yangming Stomach, Hand-Jueyin Pericardium, and Foot-Jueyin Liver blood levels. Its nature is floating but not sinking; its action is moving but not stationary. If soaked in wine, it can also guide medicinal power to the upper parts of the body (Zhang Zhongjing, in the Taiyang chapter of *Shanghan Lun* for Tiaowei Chengqi Tang, notes Dahuang should be soaked in wine; in the Yangming chapter for Dachengqi Tang, notes Dahuang should be washed with wine; in the Shaoyang-Yangming combined disease Xiaochengqi Tang, Dahuang is not processed with wine; these usages have distinct differences. Li Dongyuan said: Pathogenic factors in the upper part cannot reach their target without wine as a guide. If raw Dahuang is used, the pathogenic heat in the highest parts will be neglected. After recovery, symptoms such as red eyes, throat obstruction, headache, or heat diseases above the diaphragm may arise). Therefore, it is used to scour the intestines and stomach, purge dryness and accumulation, and remove stasis and heat.

It treats febrile diseases and epidemic diseases caused by Shanghan (Cold Damage), characterized by fever and delirious speech (delirious speech occurs due to dry feces in the Large Intestine, so purgation is indicated. "Zhan" is pronounced zhān); warm-heat type malarial fevers (Zhangnuo); dysentery with red and white discharge; abdominal pain with tenesmus; jaundice and edema; masses and accumulations (long-standing formations are called "Ji" [accumulation], belonging to Yin; those that gather and scatter irregularly are called "Ju" [aggregation], belonging to Yang. Ji often involves blood, food, or phlegm; Ju often involves Qi); retained fluids and old food retention; epigastric and abdominal fullness and stuffiness; blockage of both urination and defecation (all represent stagnation of Earth, requiring the "duo" method to drain them); hematemesis (vomiting blood) and epistaxis (nosebleed); amenorrhea and blood exhaustion; traumatic blood stasis; all types of excess heat; and latent fire within the blood. It promotes water metabolism, eliminates phlegm, erodes pus, reduces swelling, and can push out the old to bring forth the new. However, it damages Yuan Qi (Original Qi) and consumes Yin blood (excessive purgation leads to loss of Yin). It is strictly contraindicated if the disease is at the Qi level, or in patients with deficient Stomach Qi or weak blood (using it when the disease is at the Qi level constitutes punishing the innocent. Li Dongyuan said: Dahuang pushes out the old and brings forth the new, much like quelling chaos to establish peace, hence its title "General". Li Shizhen said: Zhang Zhongjing's Xiexin Tang treats vomiting and nosebleeding due to insufficient Heart Qi by using Dahuang, Huanglian (Coptidis Rhizoma), and Huangqin (Scutellariae Radix); this clears latent fire in the blood of the Pericardium, Liver, Spleen, and Stomach channels. It also treats epigastric fullness that is soft upon pressure using Dahuang Huanglian Xiexin Tang, which clears damp-heat in the Spleen and Stomach, rather than truly draining the Heart. When a disease originates from a Yin pattern and is mistakenly treated with purgation, epigastric fullness results. This is because cold has injured the Ying (Nutrient) blood, and pathogens are knotted in the Upper Jiao. The upper part of the Stomach corresponds to the heart region, hence it is called "draining the Heart". The Classics state: What arrives via the Taiyin manifests as fullness. Also: Turbid Qi remaining in the upper part generates distension. This is exactly what is meant. When a disease originates from a Yang pattern and is mistakenly treated with purgation, chest binding (Jie Xiong) results. This is because heat pathogens have sunk into the Blood level, also located in the upper epigastrium; thus, Da Xianxiong Tang and Wan both use Dahuang to clear pathogens in the Spleen and Stomach blood level and descend turbid Qi. If chest binding is at the Qi level, only Xiao Xianxiong Tang is used; if fullness is at the Qi level, only Banxia Xiexin Tang is used. One might ask: Why drain the Heart instead of tonifying it when there is insufficient Heart Qi causing bleeding? Zhu Danxi said: Insufficiency of Shaoyin leads to hyperactive Yang lacking support, causing wild movement of Yin blood; thus, Dahuang is used to drain the excessively hyperactive fire. Furthermore, the Heart itself is insufficient, while the Liver and Lung are afflicted by Fire pathogens; therefore, Huangqin is used to rescue the Lung, and Huanglian to rescue the Liver. The Lung is the master of Yin, and the Liver is the mother of the Heart and the confluence of blood. When the Fire of the Lung and Liver subsides, blood returns to its vessels and calms naturally. Kou Zongshi said: Using bitterness to drain heat is simultaneously using bitterness to tonify the Heart, achieving two goals with one move. Li Shicai said: The ancients' use of Dahuang to treat vomiting and nosebleeding from consumptive diseases was profound. Because if turbid Yin does not descend, clear Yang cannot ascend; if stasis is not removed, new blood cannot be generated).

Dahuang produced in Sichuan with brocade-like patterns is of superior quality. There are differences in processing: wine-soaked, wine-steamed, raw, and cooked. Raw usage is more potent. Huangqin (Scutellariae Radix) serves as an assistant herb (to achieve unblocking and promoting effects, one must not suddenly consume grains; Dahuang requires grain assistance to exert its unblocking effect. *Yijian Zhi* records: For scalds and burns, crush raw Dahuang, mix with vinegar, apply externally; it stops pain and leaves no scar).