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Liu Wansu, in his explication of the *Huangdi Neijing* (Yellow Emperor's Inner Canon) pathogenesis rules, stated: "All vomiting and acid regurgitation belong to heat." This refers to the upper jiao (Upper Burner) being invaded by exogenous pathogenic factors. The Stomach Qi cannot tolerate these external pathogens, thus vomiting occurs. Zhang Zhongjing treated this with Shengjiang (Fresh Ginger) and Banxia (Pinellia Rhizome).

In contrast, regarding miscellaneous diseases, when vomiting acid water occurs, it may severely soak the heart and chest, causing unbearable suffering; or secondarily, the patient vomits acid water, making the upper and lower teeth feel sour and astringent, to the point where they cannot close against each other. For such cases, treatment should employ major acrid-hot medicines, which will inevitably reduce the vomiting of acid water. The sour flavor corresponds to the qi of contraction/astringency, associated with the flourishing of Metal in the West (Lung). Water is cold, being the child element of Metal; according to the principle that "the child can make the mother full," one should use major salty-hot formulas to drain the child (Kidney Water), using acrid-hot herbs as assistants to drain the excess of Lung Metal. To treat it as heat and attack it directly, as Liu Wansu did, would be an error. In miscellaneous diseases, "vinegar heart" (acid reflux) is caused by turbid qi failing to descend, leading to central fullness; how can cold medicines treat this?

Note: Li Dongyuan classified acid regurgitation as heat in his *Yuan Bing Yuan Shi* (Source Book of Diseases and Etiologies), but here it is discussed and treated as cold. This is because Li Dongyuan believed that late-stage internal injury and deficiency diseases transmit to "cold center" (Spleen-Stomach deficiency-cold), where turbid qi fails to descend, making cold medicines unsuitable. Thus, he categorized it as cold. However, this interpretation applies the *Suwen* pathogenesis theory to exogenous pathogenic invasion, similar to the distinction between cold and heat in abdominal distension found in the *Suwen*. Referencing Zhu Danxi's discussion below, his explanation is more comprehensive.

Zhu Danxi said: Someone asked, "The *Suwen* clearly states that acid regurgitation belongs to heat, yet Li Dongyuan says it belongs to cold. Why?" I replied, "Acid regurgitation (Tu Suan) differs from swallowing acid (Tun Suan). Acid regurgitation involves vomiting acid water like vinegar. Normally, body fluids rise with ascending qi, accumulate, and stagnate. After long-term stagnation, dampness generates heat within, transforming via Fire, thus becoming sour. If it were not heat, how would this occur? However, after long stagnation, it cannot surge out spontaneously; it lies latent between the Lungs and Stomach, unable to be coughed up or swallowed down. When the muscle surface is exposed to wind-cold, internal heat becomes more constrained, and the sour flavor pierces the heart muscle; when the muscle surface is warm and pores open, or after consuming fragrant hot soups/pills, body fluids circulate, providing temporary relief. If it were not cold, why would this happen? The *Suwen* mentions 'heat' referring to the root cause; Li Dongyuan mentions 'cold' referring to the branch manifestation. However, Li Dongyuan did not account for onset triggered by external wind-cold. Instead, he based his theory on the qi of contraction (Metal) to drain Lung excess, and claimed cold medicines cannot treat acid, prescribing Anwei Tang modified with Erchen Tang, both containing Dingxiang (Clove). This approach lacks methods for treating damp-heat stagnation and does not align with classic principles. I once treated swallowing acid using Huanglian (Coptis Rhizome) and Zhuyu (Evodia Fruit), stir-fried separately, adjusting assistants and envoys according to seasons, with Cangzhu (Atractylodes Rhizome) and Fuling (Poria) as supports. These were made into small pills soaked in decoction and cooked dough balls, taken orally. I also instructed patients to nourish themselves with vegetables, which facilitated recovery.

Respectfully noted: Regarding the syndrome of acid regurgitation, from the perspective of pathogenesis, it belongs to heat; from the perspective of Zang-Fu organs, it involves disease of the Spleen and Stomach; from the perspective of internal pathogens, it is caused by phlegm-fluid retention and retained food. Therefore, treatment methods are: for heat, use cold methods; since the Spleen dislikes dampness, use bitter-dry methods; for phlegm-fluids, clear, dissipate, and separate/drain them; for retained food, digest, guide, and expel them. The *Ju Fang* (Formulas of the Bureau) failed to investigate these aspects, grouping symptoms like belching vinegar, swallowing acid, vinegar heart, and vomiting acid water under the category of Qi disorders, indiscriminately using warm-hot medicines. Does this mean acid regurgitation is exclusively due to cold without other patterns? Therefore, this section narrates the theories of Hejian (Liu Wansu), Dongyuan (Li Dongyuan), and Danxi (Zhu Zhenheng), exhaustively covering the etiology and treatment methods of this condition.

Treatment Methods for Acid Regurgitation