古经方必有主药，无之者小青龙是也。何以言之？方中麻、芍、姜、辛、桂、甘各三两
，味
、夏各半升。考古半升，约古分亦三两。仲景每以半夏半斤配生姜三两，五味半升配生姜三
两。此方正其例也。八味轻重同则不相统，故曰无主药。或谓麻黄先煎即是主药。岂知麻黄
以
有沫当去，不得不先煎，与先煎泽漆、先煎大黄有别。特以肺为水源，以此疏其壅塞耳！且
本方加减法云去麻黄者四，麻黄在可去之例岂主药乎？匪特麻黄非主药也，即桂枝亦不过因
表不解发热而用之，其与芍药、甘草同用，全乎桂枝汤矣。桂枝即非主药，芍药、甘草更
可知已，又何论半夏乎？此方本从桂枝汤来，而其
义则在干姜、五味、细辛三味。本论于柴胡汤、四逆散方下云∶咳者，加干姜、五味子、细
辛，即此方主治之义。柴胡汤方下又云∶咳者去人参、生姜、大枣，加五味子、干姜，即
此方用桂枝汤，所以必去枣、姜之义。然则小青龙为治饮家咳之方，故凡用干姜、五味子，
而与若桂若麻并施者，皆自此出。如《金匮》浓朴麻黄汤、射干麻黄汤、苓桂五味甘草姜辛
汤、苓桂五味甘草姜辛半夏汤、苓桂五味甘草姜辛半夏杏仁汤、苓桂五味甘草姜辛半夏杏仁
大黄汤六方是也。论此方所从来，当入桂枝类；论此方所由衍，当另建一类，而六方隶焉，
斯当矣。
古代经方必定有主药，没有主药的方剂就是小青龙汤。为什么这样说呢？方中麻黄、芍药、生姜、细辛、桂枝、甘草各三两，五味子、半夏各半升。考证古代的“半升”，大约相当于古代的“三两”。张仲景通常用半夏半斤配伍生姜三两，用五味子半升配伍生姜三两。这个方子正是遵循这一例证。八味药的重量相同，彼此之间无法统摄主导，所以说是没有主药。有人主张麻黄先煎就是主药。哪里知道麻黄因为煮的时候会产生浮沫需要去除，所以才不得不先煎，这与先煎泽漆、先煎大黄的情况不同。仅仅是因为肺为水之上源（水源），用这些药物来疏通肺气的壅塞罢了！而且本方的加减法中提到去掉麻黄的情况有四种，麻黄在可被去掉的范畴内，难道是主药吗？不仅麻黄不是主药，就连桂枝也不过是因为表证未解、发热而使用，它与芍药、甘草配合使用，就完全变成了桂枝汤（Cinnamon Twig Decoction）。既然桂枝都不是主药，那么芍药、甘草更不用说了，又何况半夏呢？这个方子原本是从桂枝汤演变而来，而其核心意义在于干姜、五味子、细辛这三味药。《伤寒论》在柴胡汤（Bupleurum Decoction）、四逆散（Four Inversion Powder）方后注中说：咳嗽者，加干姜、五味子、细辛，这就是本方主治的意义。柴胡汤方后注又说：咳嗽者去人参、生姜、大枣，加五味子、干姜，这正是此方使用桂枝汤时，必须去掉大枣、生姜的道理。既然如此，小青龙汤是治疗痰饮家咳嗽的方剂，所以凡是使用干姜、五味子，并与桂枝、麻黄等并用的情况，都由此衍生出来。如《金匮要略》中的厚朴麻黄汤（Magnoliae Officinalis and Ephedra Decoction）、射干麻黄汤（Belamcandae Rhizoma and Ephedra Decoction）、苓桂五味甘草姜辛汤（Poria, Cinnamon Twig, Schisandra, Licorice, Dried Ginger and Asarum Decoction）、苓桂五味甘草姜辛半夏汤（Poria, Cinnamon Twig, Schisandra, Licorice, Dried Ginger, Asarum and Pinellia Decoction）、苓桂五味甘草姜辛半夏杏仁汤（Poria, Cinnamon Twig, Schisandra, Licorice, Dried Ginger, Asarum, Pinellia and Apricot Seed Decoction）、苓桂五味甘草姜辛半夏杏仁大黄汤（Poria, Cinnamon Twig, Schisandra, Licorice, Dried Ginger, Asarum, Pinellia, Apricot Seed and Rhubarb Decoction）这六个方子就是例子。讨论这个方子的来源，应当归入桂枝汤类；讨论这个方子的衍变，应当另立一类，并将上述六方隶属其中，这才是恰当的。
Ancient classical formulas must have a chief herb; the Xiao Qing Long Tang (Minor Blue Dragon Decoction) is an exception where no single chief herb exists. Why is this so? In this formula, Mahuang (Ephedrae Herba), Shaoyao (Paeoniae Radix Alba), Shengjiang (Zingiberis Rhizoma Recens), Xixin (Asari Radix et Rhizoma), Guizhi (Cinnamomi Ramulus), and Gancao (Glycyrrhizae Radix et Rhizoma) are each used in the amount of three liang, while Wuweizi (Schisandrae Fructus) and Banxia (Pinelliae Rhizoma Preparatum) are each used in the amount of half sheng. Historical research indicates that ancient "half sheng" is approximately equivalent to three liang. Zhang Zhongjing typically paired Banxia (Pinelliae Rhizoma Preparatum) half jin with Shengjiang (Zingiberis Rhizoma Recens) three liang, and Wuweizi (Schisandrae Fructus) half sheng with Shengjiang (Zingiberis Rhizoma Recens) three liang. This formula follows this precedent exactly. Since the weights of all eight herbs are identical, they cannot dominate or control one another; therefore, it is said to lack a chief herb. Some argue that because Mahuang (Ephedrae Herba) is boiled first, it serves as the chief herb. However, Mahuang (Ephedrae Herba) requires pre-boiling specifically to remove the foam that forms, which is distinct from the pre-boiling of Zeqi (Phytolaccae Radix) or Dahuang (Rhei Radix et Rhizoma). It is merely used because the Lung is the source of water fluids, and these herbs are employed to unblock pulmonary congestion. Furthermore, the modification rules for this formula mention four instances where Mahuang (Ephedrae Herba) is removed. If Mahuang (Ephedrae Herba) can be removed, how can it be the chief herb? Not only is Mahuang (Ephedrae Herba) not the chief herb, but Guizhi (Cinnamomi Ramulus) is also used only when the exterior syndrome remains unresolved accompanied by fever. When combined with Shaoyao (Paeoniae Radix Alba) and Gancao (Glycyrrhizae Radix et Rhizoma), it essentially becomes Guizhi Tang (Cinnamon Twig Decoction). If Guizhi (Cinnamomi Ramulus) is not the chief herb, then Shaoyao (Paeoniae Radix Alba) and Gancao (Glycyrrhizae Radix et Rhizoma) certainly are not, let alone Banxia (Pinelliae Rhizoma Preparatum). This formula originally derives from Guizhi Tang (Cinnamon Twig Decoction), and its core therapeutic significance lies in the combination of Ganjiang (Zingiberis Rhizoma), Wuweizi (Schisandrae Fructus), and Xixin (Asari Radix et Rhizoma). The Shanghan Lun states under the Chaihu Tang (Bupleuri Decoction) and Sini San (Four Reversal Powder) sections: for cough, add Ganjiang (Zingiberis Rhizoma), Wuweizi (Schisandrae Fructus), and Xixin (Asari Radix et Rhizoma); this reflects the main indication of this formula. Under the Chaihu Tang (Bupleuri Decoction) section, it further states: for cough, remove Renshen (Ginseng Radix), Shengjiang (Zingiberis Rhizoma Recens), and Dazao (Jujubae Fructus), and add Wuweizi (Schisandrae Fructus) and Ganjiang (Zingiberis Rhizoma); this explains why, when using Guizhi Tang (Cinnamon Twig Decoction) as the base for this formula, Dazao (Jujubae Fructus) and Shengjiang (Zingiberis Rhizoma Recens) must be removed. Thus, Xiao Qing Long Tang (Minor Blue Dragon Decoction) is a formula for treating cough due to fluid retention. Consequently, any instance where Ganjiang (Zingiberis Rhizoma) and Wuweizi (Schisandrae Fructus) are used in conjunction with Guizhi (Cinnamomi Ramulus) or Mahuang (Ephedrae Herba) stems from this principle. Examples include the six formulas found in the Jin Gui Yao Lue: Houpo Mahuang Tang (Magnoliae Officinalis and Ephedra Decoction), Shegan Mahuang Tang (Belamcandae Rhizoma and Ephedra Decoction), Linggui Wugan Jiangxin Tang (Poria, Cinnamon Twig, Schisandra, Licorice, Dried Ginger and Asarum Decoction), Linggui Wugan Jiangxin Banxia Tang (Poria, Cinnamon Twig, Schisandra, Licorice, Dried Ginger, Asarum and Pinellia Decoction), Linggui Wugan Jiangxin Banxia Xingren Tang (Poria, Cinnamon Twig, Schisandra, Licorice, Dried Ginger, Asarum, Pinellia and Apricot Seed Decoction), and Linggui Wugan Jiangxin Banxia Xingren Dahuang Tang (Poria, Cinnamon Twig, Schisandra, Licorice, Dried Ginger, Asarum, Pinellia, Apricot Seed and Rhubarb Decoction). Regarding the origin of this formula, it should be classified under the Guizhi Tang category; regarding its derivation, it should establish a new independent category to which these six formulas belong. This classification would be appropriate.