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Treats Taiyang disease (disease of the Taiyang channel) where wind-cold pathogens are in the exterior, presenting with stiffness and pain in the head and nape, fever, body ache, lower back pain, joint pain, aversion to wind and cold, absence of sweating, chest fullness with wheezing, and a floating-tight or floating-rapid pulse. Use this formula to induce sweating. Even if these symptoms are present, if the pulse is floating and weak, there is spontaneous sweating, or the Chi (cun-kou position on the radial artery corresponding to the lower jiao/kidney) pulse is faint and slow, it must not be used. It is most suitable for Bi syndrome (obstruction syndrome) caused by wind, cold, and dampness; lung meridian congestion leading to confusion and inability to speak; and asthma/wheezing caused by cold wind.

Ephedrae Herba (Mahuang, 麻黄) [remove joints] 3 liang
Cinnamomi Ramulus (Guizhi, 桂枝) 2 liang
Glycyrrhizae Radix et Rhizoma (Gancao, 甘草) [roasted] 1 liang
Pruni Semen (Xingren, 杏仁) [remove skin and tips] 60 seeds

The above four ingredients: Take nine sheng of water, first decoct Ephedrae Herba until reduced by two sheng, remove the foam from the surface, add the remaining herbs, and decoct to obtain two and a half sheng of liquid. Strain the dregs, and take eight he of the decoction warm. Cover warmly to induce slight sweating; there is no need to drink hot porridge. After one dose, if sweating occurs, stop taking the remaining medicine. If sweating is excessive, apply warm powder to the body.

[Annotation] Whenever wind-cold pathogens are in the exterior, with a floating-tight-rapid pulse and absence of sweating, all constitute Exterior Excess patterns (Biao Shi), which should be primarily treated with Mahuang Tang (Cinnamon Twig Decoction). It is named Mahuang Tang because Ephedrae Herba serves as the Sovereign herb. Ephedrae Herba is warm in nature, pungent and bitter in taste, and its action is rapid ascent and dispersion. Cinnamomi Ramulus is warm in nature, pungent and sweet in taste, and its function is to secure the exterior. Since the pattern belongs to excess, using Ephedrae Herba as the primary agent is the strategy for victory; using Cinnamomi Ramulus as the Minister herb demonstrates the subtlety of regulation and restraint. The bitter-warm nature of Pruni Semen assists Ephedrae Herba in expelling pathogens and descending rebellious qi. The sweet-pure nature of Glycyrrhizae Radix et Rhizoma assists Cinnamomi Ramulus in harmonizing the interior and repelling the exterior. Upon entering the stomach, the qi circulates through Yuanfu (pores/interstitial spaces), and essence is transported to the skin and hair. Thus, the skin and vessels combine their essence, and sweat flows profusely. Pathogens in the exterior will be completely eliminated without retention, pain ceases, wheezing subsides, and cold-heat symptoms resolve instantly. There is no need to drink porridge to rely on grain qi for sweat generation. The reason ginger and jujube are not used is that the nature of Zingiberis Rhizoma Recens (Shengjiang, fresh ginger) disperses horizontally in the muscles, hindering the rapid ascent of Ephedrae Herba; the nature of Ziziphi Jujubae Fructus (Dazao, jujube) is sticky and stagnant in the diaphragm, hindering the rapid descent of Pruni Semen. This is to achieve rapid direct action; any delay makes it less rapid, and horizontal dispersion prevents ascent. However, this is a purely Yang formula with overly strong dispersing power, like a general charging straight ahead with a single sword. If used appropriately, success is achieved in one battle; if misused, failure to restrain leads to disaster. Therefore, it can be taken only once, not twice. If the condition persists after sweating, Guizhi Tang (Cinnamon Twig Decoction) should be substituted. This formula is Zhang Zhongjing's first potent drug for opening the exterior, expelling pathogens, and inducing sweating. Unskilled physicians do not understand that its potency lies in covering warmly to induce sweating; without warm covering, it is not potent. The world says Ephedrae Herba specializes in releasing the exterior and does not treat other diseases. They do not know that when this decoction is combined with Guizhi Tang, it is named Mahuang Guizhi Ban Tang (Half-Mahuang Half-Cinnamon Twig Decoction), used to harmonize lingering cold-heat in the Taiyang channel. When Pruni Semen is removed and Shizui Gypsum (Shigao, gypsum fibrosum) is added to Guizhi Tang, it is named Guizhi Er Yuebi Yi Tang (Two-Guizhi One-Yuebi Decoction), used to resolve cold-heat where heat predominates over cold in the Taiyang channel. If yang is abundant internally with no sweating, there is also Mahuang Xingren Gancao Shigao Tang (Ephedra Apricot Seed Licorice Gypsum Decoction), used to disperse pathogens in the Taiyin Lung. If yin is abundant internally with no sweating, there is also Mahuang Fuzi Xixin Gancao Tang (Ephedra Aconite Asarum Licorice Decoction), used to warm and disperse cold in the Shaoyin Kidney. In *Jingui Yaolue* (Essential Prescriptions of the Golden Cabinet), this formula has Cinnamomi Ramulus removed; in *Qianjin Fang* (Prescriptions Worth a Thousand Gold), Cinnamomi Ramulus is replaced by Cinnamomum Cassia Bark (Rougui, cinnamon bark); both are named Huanhun Tang (Soul-Recovering Decoction), used to treat pathogens in the Taiyin channel causing sudden syncope, locked jaw, and cessation of breathing, taking effect upon swallowing. None of these require warm covering to induce sweating. Thus, we know that the potency of Mahuang Tang depends on whether warm covering is applied. This is the secret method of Zhang Zhongjing in using formulas; how could ordinary people fathom it!