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Shu Di Huang (Prepared Rehmanniae Radix), with a sweet taste and warm nature, is heavy and sinking. It belongs to the category of "Yang within Yin" and is non-toxic. It enters the Liver and Kidney meridians. It generates blood, nourishes essence, and promotes the growth of marrow in the bones and brain.

The Qi of True Yin cannot be generated without it, and the flames of Deficient Fire cannot be subdued without it. Indeed, it is a miraculous substance that saves lives and a wonderful flavor that prolongs longevity. People discard it because they consider it cloying and obstructive, failing to understand its efficacy. The Kidney is only suited for tonification and not for purgation; thus, the Kidney must certainly be tonified. However, there are few herbs suitable for tonifying the Kidney. Besides Cornus Officinalis Fructus (Shanzhuyu, 山茱萸), Achyranthes Bidentatae Radix (Niuxi, 牛膝), Eucommia Ulmoides Cortex (Duzhong, 杜仲), and Schisandra Chinensis Fructus (Beiwuweizi, 北五味子), what other herb can be used besides Shu Di Huang? Moreover, Cornus Officinalis Fructus and Achyranthes Bidentatae Radix cannot serve as the Sovereign herb (Jun Yao, 君药), while Eucommia Ulmoides Cortex is too warm in nature; it can tonify the decline of Kidney Yang but cannot replenish the deficiency of Kidney Yin. This is why Shu Di Huang must be used. As a Sovereign herb, Shu Di Huang can be used from one liang up to eight liang. Generally, the usage of Yin-tonifying herbs differs significantly from Yang-tonifying herbs. Yang-tonifying herbs can achieve results with small doses, whereas Yin-tonifying herbs require large doses to be effective. This is because Yang governs ascending and Yin governs descending. When Yang ascends, a small dose of Yang herb allows Qi to rise easily; when Yin descends, a small dose of Yin herb makes it difficult for the medicinal flavor to reach the lower body. Shu Di Huang is an herb of extreme Yin, distinct from other Yin herbs; without using it in large quantities, how can it succeed? Some argue: Shu Di Huang is an herb of extreme Yin, and its nature is very stagnant. Using it in large quantities may cause chest oppression and generate phlegm; if it exacerbates phlegm leading to asthma, it would be very dangerous. This shows a lack of understanding of Shu Di Huang's power. Since Shennong tasted the herbs, the discussion of this herb was lost, causing later generations to be unaware of its secrets. Although many famous doctors of past dynasties have elucidated its properties, they have rarely revealed its profound mysteries. Does Shu Di Huang merely avoid generating phlegm? It can actually eliminate phlegm. Does it merely avoid stagnating Qi? It excels at promoting Qi movement. It depends on how people use it. Phlegm originates differently from the five Zang organs. If phlegm comes from the Spleen or Lung, using Shu Di Huang may aggravate dampness, making it seemingly unsuitable. However, if phlegm originates from the Heart, Liver, or Kidney, what else can be used to expel it besides Shu Di Huang? For instance, some patients expectorate phlegm like clear water. Treatments with Er Chen Tang (Two-Cured Decoction) and other phlegm-resolving drugs fail hundred times out of a hundred. Yet, after taking Ba Wei Wan (Eight-Ingredient Pill), the surging phlegm subsides instantly. Is this not clear evidence that Shu Di Huang treats phlegm from the Heart, Liver, and Kidney? [Commentary: Heart Fire stagnation, Liver Qi rebellion, and Kidney Water depletion can all generate phlegm, which only Shu Di Huang can resolve.] Another type involves expectorating white foam day and night, lighter in the morning and heavier at night, severe enough to prevent lying down. Using Liu Wei Wan (Six-Ingredient Pill) with a large addition of Shu Di Huang and Cornus Officinalis Fructus, after several doses, the phlegm decreases significantly. After dozens more doses, the white foam disappears completely, and sleep becomes peaceful. Is this not further proof of Shu Di Huang's ability to resolve phlegm? There is no doubt that Shu Di Huang resolves phlegm without generating it. Regarding Qi stagnation, if Dihuang Tang (Rehmannia Decoction) resolves phlegm instantly, how can one claim that Qi does not move? [Commentary: Shu Di Huang moves Qi without stagnating it; this argument truly breaks new ground.] In human digestion, the Qi of the Spleen and Kidney facilitates the transformation of food and water. If the Spleen and Kidney are strong, food transforms into Essence rather than Phlegm. Due to Spleen and Kidney deficiency, food transforms into Phlegm instead of Essence. Patients whose phlegm is resolved by Dihuang Tang often regain their appetite, proving that Shu Di Huang is a sacred item for opening the stomach. Why can it open the stomach? The Stomach is the gate of the Kidney. When Kidney Water is abundant, Stomach fluids are naturally moistened. Thus, sufficient Kidney Qi leads to sufficient Stomach Qi; rising Kidney Qi leads to rising Stomach Qi. Therefore, Shu Di Huang moves Qi rather than stagnating it, which should be universally accepted. With moving Qi and resolving phlegm, how could asthma arise? This needs no doubt. [Commentary: In individuals with Yin deficiency, Stomach Qi is closed; using Shu Di Huang反而 increases hunger and desire for food, as Stomach Yin pathogens dissipate and Righteous Qi extends, thus opening the stomach.]

Someone asks: Since Shu Di Huang is a Sovereign herb, can it be used alone to achieve efficacy? Answer: Although Shu Di Huang is a Sovereign herb, it should not be used alone to succeed. Yang herbs can be used in odd-numbered combinations, but Yin herbs must be used in even-numbered combinations. Moreover, Shu Si Huang is an extreme Yin substance with pure nature. Without assisting it with herbs of biased nature, success is impossible. This is why Si Wu Tang (Four-Substance Decoction) must include Angelica Sinensis Radix (Danggui, 当归), Paeonia Lactiflora Radix Alba (Baishao, 白芍), and Chuanxiong Rhizoma (Chuanxiong, 川芎) to tonify blood. Extending this principle: combined with Ginseng Radix et Rhizoma (Renshen, 人参), it tonifies the mutual interaction of Heart and Kidney; combined with Atractylodis Macrocephalae Rhizoma (Baizhu, 白术), it tonifies Spleen and Kidney deficiencies; combined with Ophiopogon Japonicus Radix (Maidong, 麦冬) and Schisandra Chinensis Fructus (Wuweizi, 五味子), it nourishes the drying Lung and Kidney; combined with Paeonia Lactiflora Radix Alba (Baishao, 白芍), it benefits the nearly exhausted Liver and Kidney; combined with Cinnamomi Cortex (Rougui, 肉桂), it assists the declining Fire of the Gate of Vitality (Mingmen, 命门); combined with Ziziphus Jujube Seed (Suanzaoren, 酸枣仁), it calms the boiling Fire in the Epigastrium (Shanzhong, 膻中); combined with Sanguisorbae Radix (Diyu, 地榆), it clears Blood heat in the Large Intestine; combined with Glehniae Radix (Shashen, 沙参), it cools inflammation in the Stomach; combined with Scrophulariae Radix (Xuanshen, 玄参), it drains the flames of the Yangming channel. However, Shu Di Huang must be used as the Sovereign herb in amounts of one to two liang, with assisting herbs added in amounts of five or eight qian, ensuring complete success. If Shu Di Huang is used in small amounts, its power is incomplete, and it cannot succeed. Only Cinnamomi Cortex (Rougui, 肉桂) should be limited to one or two qian, not exceeding three qian; other herbs can be used in larger quantities alongside Shu Di Huang without禁忌.

Someone asks: Shu Di Huang is essential for tonifying blood before childbirth; can it also be heavily used after childbirth? Answer: Heavy use is precisely indicated after childbirth. Postpartum women suffer from severe blood loss. What herb can generate new blood if not Shu Di Huang? Although Fo Shou San (Buddha's Hand Powder) is a sacred postpartum remedy, adding Shu Di Huang makes its blood-generating effect even more miraculous. For various postpartum conditions like syncope due to blood loss, combining it with Ginseng Radix et Rhizoma (Renshen, 人参) and Angelica Sinensis Radix (Danggui, 当归) yields remarkable results, not just for those with urgent abdominal pain. The Original Qi in the Kidney is the ancestor of Postnatal Qi. Shu Di Huang is born bearing Pre-natal Qi. Postpartum women deplete the Blood Chamber and exhaust Original Qi. Since Postnatal blood cannot be quickly regenerated, it relies on Pre-natal Qi to generate it. Using Shu Di Huang to assist the Postnatal aspect contains profound principles, not mere generalizations.

Someone asks: People believe Shu Di Huang is cloying and generates phlegm; is it acceptable to process it with Ginger Juice (Jiangzhi, 姜汁) and Amomum Fruit (Sharen, 砂仁)? Answer: Consider whether Shu Di Huang is ever cloying. Shu Di Huang is sweet and warm. Sweetness is favored by the Spleen and Stomach; warmth is suitable for them. Since the Spleen and Stomach do not conflict with it, why would it cause cloying obstruction? Furthermore, Shu Di Huang is an herb of the Yin aspect. It either stays in the Stomach or moves to the Kidney. The Stomach is the gate of the Kidney. When the Stomach encounters the flavor of the Kidney meridian, it guides it to the Kidney. The idea of cloying obstruction arises from those who do not understand medical principles and should not confuse experts. Although Ginger Juice opens the stomach and Amomum Fruit awakens the Spleen, neither hinders Shu Di Huang, yet one cannot say Shu Di Huang causes cloying obstruction and generates phlegm. [Commentary: Since the emergence of the theory that it causes cloying obstruction and generates phlegm, people feared Shu Di Huang and dared not use it. Now, with Far Gong's elucidation, confusion can be dispelled.]

Some say: If Shu Di Huang is not cloying, why are Poria (Fuling, 茯苓), Dioscorea Hypoglauca Rhizome (Shanyao, 山药), and Alisma Orientale Rhizome (Zexie, 泽泻) added to Liu Wei Di Huang Wan (Six-Ingredient Rehmannia Pill)? Isn't it because of its cloying nature? To view Poria, Dioscorea Hypoglauca Rhizome, and Alisma Orientale Rhizome merely as agents to restrain Shu Di Huang is to underestimate them greatly. The Kidney is suited for tonification, not purgation. If we use Shu Di Huang to tonify the Kidney, how can we use diuretics to purge the Kidney? And using diuretics to restrain a Kidney-tonifying herb creates purgation without tonification. It is clear that Shu Di Huang should not be restrained. Consequently, the use of Poria, Dioscorea Hypoglauca Rhizome, and Alisma Orientale Rhizome is not to restrain Shu Di Huang, nor is it due to Shu Di Huang's cloying nature. Then, what is the purpose of these three herbs? Shu Di Huang can nourish Yin but not remove dampness; it can tonify Water but not generate Yang. These three herbs are used to assist its success, not to hinder it.

Someone asks: If Shu Di Huang is not cloying, why does it generate phlegm? Did previous authors speak without basis? Answer: Shu Di Huang is truly a sacred herb for resolving phlegm, yet the world obscures its merit, which is why I insist on refuting this. Phlegm generation starts with Kidney Qi deficiency, and phlegm formation depends on weak Stomach Qi. If Kidney Qi is not deficient, Stomach Qi is not weak. If the Kidney is not deficient, phlegm has no source; if the Stomach is not weak, phlegm has no means of formation. To prevent phlegm formation, one must tonify the Stomach; to prevent phlegm generation, one must tonify the Kidney. When Kidney Qi is sufficient, Stomach Qi is sufficient; the Kidney has no phlegm, so the Stomach has no phlegm. Shu Di Huang, though a Kidney-tonifying herb, is also a Stomach-tonifying herb. Stomach fluids originate from the Kidney. Tonifying the Kidney generates Stomach fluids, allowing True Water to ascend to the Stomach. When True Water ascends, Evil Water in the Stomach cannot survive. Accumulations transform, and saliva/phlegm dissolves, achieving a subtle effect unknowingly. Is it not true that Shu Di Huang resolves phlegm? How can it be said to cause cloying obstruction and generate phlegm?

Someone asks: Shu Di Huang tonifies Kidney Water; why add Dioscorea Hypoglauca Rhizome (Shanyao, 山药) and Cornus Officinalis Fructus (Shanzhuyu, 山茱萸)? Answer: Kidney Water cannot be generated without sour flavors. Cornus Officinalis Fructus is sour and warm, complementing Shu Di Huang like milk and water. However, its sourness is excessive; without the sweet-warm nature of Shu Di Huang, it cannot independently generate Kidney Water. Their combination is harmonious, like a marital union, achieving the state of Mutual Interaction (Ji Ji, 既济).

Someone asks: In Ba Wei Di Huang Wan (Eight-Ingredient Rehmannia Pill), why is Shu Di Huang the Sovereign herb? Answer: Ba Wei Di Huang Wan tonifies Kidney Fire. However, Fire cannot be tonified alone; it must be tonified within Water. Since tonifying Fire requires tonifying Water, the water-tonifying herb must be the Sovereign. Among the formula's ingredients, only Shu Di Huang is the sacred herb for tonifying Water, hence it serves as the Sovereign. With a Sovereign, there are Ministers; Dioscorea Hypoglauca Rhizome and Cornus Officinalis Fructus assist it. With Ministers, there are Guides and Messengers; Paeonia Moutan Cortex (Danpi, 丹皮), Alisma Orientale Rhizome (Zexie, 泽泻), and Poria (Fuling, 茯苓) follow. Cinnamon Twig (Guizhi, 桂枝) and Aconite Root (Fuzi, 附子) resemble guests. They wish to tonify Fire but lack autonomy, yielding precedence to Shu Di Huang to tonify Fire via tonifying Water.

Someone asks: Can Shu Di Huang be used alone to treat disease? Answer: Yes. For diseases of Heart-Kidney Non-Interaction, using two liang of Shu Di Huang, decocted and taken on an empty stomach, brings the Heart and Kidney into immediate interaction. People think Shu Di Huang only enters the Kidney meridian, not knowing it connects upward to the Heart. Heart-Kidney Non-Interaction usually involves excessive Heart Fire and severe Kidney Water deficiency. Shu Di Huang nourishes the dryness in the Kidney. Nourished by Water, Kidney fluids ascend to benefit the Heart. Benefited by the Kidney, Heart Qi descends to interact with the Kidney. What need is there for Coptis Rhizome (Huanglian, 黄连) and Cinnamon Twig (Guizhi, 桂枝)?

Someone asks: If Shu Di Huang can succeed alone, can one make pills of single-shard Shu Di Huang for Heart-Kidney Non-Interaction and take them morning and night? Answer: This is inappropriate. Single-use of Shu Di Huang is for occasional surprise effects. For long-term success, it must be assisted by Polyporus (Fushen, 茯神) and Dioscorea Hypoglauca Rhizome (Shanyao, 山药), and guided by Cornus Officinalis Fructus (Shanzhuyu, 山茱萸) and Ziziphus Jujube Seed (Suanzaoren, 酸枣仁).

Someone asks: Should Shu Di Huang be used in large or small doses? Answer: It should be used in large doses, not small. However, proper usage matters. Even heavy doses of several liang are not too much if used correctly; even small doses of several qian are too much if used incorrectly. Used during severe Kidney Water deficiency, even large doses feel insufficient. Used during massive Spleen Earth collapse, even small doses feel excessive. Used for boiling Kidney Fire, even large doses feel lacking. Used for Stomach Earth wheezing and distension, even small doses feel disliked. Success depends entirely on proper usage; quantity is secondary.

Someone doubts: Shu Di Huang is cloying and stagnating; excessive Yin tonification may hinder function, so it shouldn't be used alone. Yet predecessors succeeded with single herbs. Why? Answer: Single-use of Shu Di Huang is a temporary expedient for surprising results. It is superior to combine it with other herbs for better efficacy. For Heart-Kidney deficiency, add Longan Aril (Longyanrou, 龙眼肉); for Liver-Kidney deficiency, add Paeonia Lactiflora Radix Alba (Baishao, 白芍); for Lung-Kidney deficiency, add Ophiopogon Japonicus Radix (Maidong, 麦冬); for Spleen-Kidney deficiency, add Ginseng Radix et Rhizoma (Renshen, 人参) or Paeonia Lactiflora Radix Alba (Baishao, 白芍). This avoids cloying obstruction and yields faster results, depending on clinical flexibility. [Commentary: This opens countless methods.]

Someone doubts: Kidney deficiency suits Shu Di Huang (tonifying Yin with Yin), but why is it also used for Stomach and Gallbladder deficiency? Answer: This is an ancient expedient but also a highly appropriate method. The Stomach is the gate of the Kidney. Kidney deficiency leads to Stomach deficiency; tonifying the Kidney is indeed tonifying the Stomach. The Gallbladder attaches to the Liver, but its juice requires Kidney fluid infiltration to avoid drying up. Kidney deficiency leads to Gallbladder deficiency; tonifying the Kidney is indeed tonifying the Gallbladder. If one sees Stomach deficiency and uses only Stomach-tonifying herbs, aromatic-dry substances will further scorch Kidney Water. If one sees Gallbladder deficiency and uses only Gallbladder-tonifying herbs, sour-astringent agents will further deplete Kidney Water. With depleted Kidney Water, the Stomach and Gallbladder become weaker. Only by tonifying the Kidney with Shu Di Huang can the Stomach and Gallbladder draw sufficient support, remaining moist and hydrated. Who says Yang syndromes should not be treated with Yin tonification?

Someone doubts: Shu Di Huang is an extreme Yin herb; using it heavily to nourish the Kidney is appropriate. But why did ancients use it effectively for extreme Yang diseases? Is Shu Di Huang a Yang herb? Answer: Shu Di Huang is not a Yang herb. Using a non-Yang herb for Yang diseases works because Yang is balanced by Yin. Yang cannot settle without Yin. Using Shu Di Huang to capture extreme Yang Qi allows Water to ascend and Fire to descend, achieving the beauty of Mutual Interaction (Ji Ji, 既济).

Someone doubts: Shu Di Huang nourishes Yin but doesn't open the stomach. Who knew it was a sacred herb for opening the stomach? The Stomach is the gate of the Kidney. When the Kidney is withered, it relies on the Stomach gate to transport food and water to relieve distress. Would the Stomach reject what the Kidney desires? Moreover, with Kidney deficiency and lack of Water, the Stomach is filled with Fire, longing for True Yin Water to save it from drought. Thus, Shu Di Huang is pleasing to both the Stomach and the Kidney. Why would the Stomach not eagerly open its gates to welcome it? Therefore, Kidney-deficient patients must use Shu Di Huang to open the stomach. If Kidney Water is not deficient and there is no Fire in the Stomach, sudden use of Shu Di Huang may cause slight bloating; this is improper usage. Who says Shu Di Huang closes the stomach?