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The *Neijing* states: Juyang (Taiyang, the Greater Yang channel) is the leader of all Yang channels. Its vessels connect to the Fengfu acupoint (GV16), thus it governs the Qi of all Yang channels. It also states: On the first day of a Shanghan (Cold Damage) disease, the Juyang channel receives the pathogen. Symptoms include pain in the head and nape, and stiffness in the lower back and spine. This is because this channel descends from the head and nape, passes through the shoulders, flanks the spine, and reaches the middle of the waist. Its jurisdiction is broad, and its pathway is long; therefore, it is easily invaded by pathogens. Once invaded, aversion to cold and fever occur, and these symptoms are more severe than in other channels. Zhang Zhongjing uses Mahuang Tang (Ephedra Decoction) to induce sweating and release the exterior. This applies when there are Taiyang symptoms, so Taiyang-specific herbs are used. If the disease is in the Yangming channel, heat predominates over cold, and the aforementioned symptoms would not be present. If the disease is in the Shaoyang channel, there is alternating chills and fever, and again, the aforementioned symptoms would not be present. If the pathogen transmits to the Three Yin channels, there is only heat without cold, and even less likely to have the aforementioned symptoms. Therefore, only in the Taiyang channel is the cold sensation particularly intense, the pulse particularly tight, and anhidrosis (absence of sweating) particularly prominent. Before transmitting to Yangming, there is no thirst; before transmitting to Shaoyang, there is no deafness. Zhang Zhongjing employs Mahuang Tang as the standard treatment for Taiyang diseases. This is indeed not replaceable by Jiwei Qianghuo Tang (Nine-Ingredient Notopterygium Decoction) created by Yi Lao (Wang Haogu). If it is not a Taiyang disease but a Yangming disease, Gegen Tang (Pueraria Decoction) should be used; if it is not a Taiyang disease but a Shaoyang disease, Chaihu Tang (Bupleurum Decoction) should be used. None of these can borrow or substitute for Mahuang Tang. Nevertheless, the Taiyang channel is not only susceptible to invasion by severe cold in winter; cold pathogens in all four seasons can invade it. If upon invasion the body is indeed cold, the pulse is indeed tight, and symptoms are complete, then Mahuang may be used regardless of the season. If upon invasion the cold is not severe, and the pulse is not notably tight, even if symptoms are present, Mahuang may be omitted even in winter. Furthermore, for individuals who are exhausted from labor or whose original Qi is depleted after illness, if they accidentally contract a cold pathogen and present with a tight pulse but weak strength, one must apply flexible treatment strategies rather than rigidly adhering to the use of Mahuang. This is because Mahuang possesses a fierce and potent nature; while it easily attacks pathogens, it readily damages healthy Qi. A single misapplication can lead to unpredictable complications; how can one not be cautious?

Note: Mahuang Tang is the primary medicine for the Taiyang channel. I emphasize caution repeatedly because if the timing, the channel, or the patient's constitution does not match the indication, harm is rarely avoided. Please do not experiment lightly; this would be a great fortune for the world.

Clinical Cases:
A friend, after accumulating fatigue, contracted cold and developed fever. The physician failed to examine carefully and administered Mahuang Tang. This resulted in red eyes, epistaxis (nosebleed), and blood in the sputum. Subsequently, Xiaochaihu Tang (Minor Bupleurum Decoction) was given, leading to a dry tongue lacking fluids. Upon my examination, the pulse was deficient, rapid, and weak, indicating a pattern of fatigue combined with Yin deficiency. Misadministration of hot-natured drugs inevitably caused bleeding and exhaustion of fluids. After administering Dihuang Tang (Rehmannia Decoction) for three doses, the bleeding stopped, but mental clarity had not returned. I prescribed Shengmai San (Generate the Pulse Powder) and Guipi Tang (Restore the Spleen Decoction) with Baizhu (Atractylodis Rhizoma) removed. Although the spirit settled, the tongue still failed to produce fluids. I stated: "The Kidney governs the five fluids, and the Lung is the source of production and transformation." Why did both nourishing Yin and tonifying Qi fail? After deep contemplation, I realized that Mahuang's nature does not retain inward; despite administration, no sweat occurred. It merely injured Yin, causing bleeding from the mouth and nose, while the medicinal properties were never vented outward. Consequently, fluid metabolism remained stagnant. I continued using Shengmai San to secure the root, and added Gegen (Puerariae Radix) and Chenpi (Citri Reticulatae Pericarpium) to guide the Qi. Thus, mild sweating ensued, and fluids finally appeared on the tongue. The patient recovered later with Guipi Tang and Liuwei Wan (Six-Ingredient Rehmannia Pill).

A physician, arrogant by nature, contracted cold in autumn. He self-administered two doses of Mahuang Tang. This led to red eyes, cracked lips, and disregard for propriety (exposing nakedness). Ultimately, he developed a complex disorder (Huai Zheng).

A herbal merchant caught a wind-cold. Believing himself knowledgeable about medicines, he ingested five qian of Mahuang. He suffered continuous hematemesis (vomiting blood) and died. For these two cases, even the administration of Huanglian Jiedu Tang (Coptis Decoction to Relieve Toxicity) and Xijiao Dihuang Tang (Rhinoceros Horn and Rehmannia Decoction) could not save them. This is truly terrifying.

Mahuang Tang Formula:
Mahuang (Ephedrae Herba, 2 qian)
Guizhi (Cinnamomi Ramulus, 1 qian)
Gancao (Glycyrrhizae Radix et Rhizoma, 0.5 qian)
Xingren (Armeniacae Semen Amarum, 8 grains)
Decoct with water, adding fresh ginger and jujube.

Jiwei Qianghuo Tang Formula:
Qianghuo (Notopterygii Rhizoma et Radix)
Fangfeng (Saposhnikoviae Radix)
Cangzhu (Atractylodis Rhizoma) (each 1 qian)
Gancao (Glycyrrhizae Radix et Rhizoma)
Baizhi (Angelicae Dahuricae Radix)
Chuanxiong (Ligustici Chuanxiong Rhizoma)
Shengdihuang (Rehmanniae Radix)
Huangqin (Scutellariae Radix) (each 1.5 qian)
Xixin (Asari Radix et Rhizoma) (0.7 qian)
Decoct with water, adding fresh ginger and jujube.