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*Shanghan Lun* (Treatise on Cold Damage) was originally a book for treating cold damage, yet it discusses wind-stroke first because wind-stroke can also be named cold damage (*Nan Jing* states: "There are five types of cold damage; including wind-stroke, cold damage, damp-warmth, heat disease, and warm disease"). However, upon investigation, it is different from true cold damage. Generally, wind-stroke is mild while cold damage is severe. Because of its severity, treatment must employ potent medicinal strength to be effective. What is meant by "potent" refers to *Mahuang Tang* (Ephedra Decoction) in *Shanghan Lun*. Now, let us discuss the syndrome of *Mahuang Tang* and the rationale behind its formulation, and elaborate on the methods of flexible modification when using *Mahuang Tang*.

Original text of *Shanghan Lun*: In Taiyang disease (disease pattern caused by pathogenic factors invading the Taiyang channel), whether fever has already appeared or not, there will inevitably be aversion to cold, body pain, vomiting and regurgitation, and a tight pulse at all positions (cun, guan, chi). This is named cold damage.
Another original text: In Taiyang disease, with headache, fever, body pain, lower back pain, joint pain, aversion to wind, absence of sweating, and wheezing, *Mahuang Tang* (Ephedra Decoction) should be used as the primary treatment.

A tight pulse at all positions is indeed a definitive sign of cold damage. However, the sensation of a tight pulse is hardest to describe; only by thoroughly understanding its pathology can one easily imagine and grasp it. The pulse originates from the Heart; when the Heart beats, it pumps blood outward, causing the entire body's vessels to pulsate. The movement resembles waves rising and falling. Logically, the greater the force of the pulse, the more pronounced its rising and falling momentum should be. As for the tight pulse, its beating seems forceful yet appears to lack fluctuation. Investigating the reason, it is actually because Taiyang represents the defensive Yang Qi of the exterior. When attacked by cold, this Qi is forced inward to merge with the vessels. The vessels receive the accumulated heat of Taiyang and should naturally rise and fall forcefully to create a responsive momentum. However, the constricting force of the cold simultaneously compresses the vessel pathways, preventing them from rising and falling. Therefore, upon palpation, the pulse feels very forceful but passes straight through without resistance. Furthermore, due to the inability to fluctuate, the accumulated energy creates a tendency to flicker left and right. This is the true image of a tight pulse.

Regarding the syndrome of *Mahuang Tang*, whole-body pain occurs because the muscles and bones cannot withstand the constriction of cold (as iron bars shorten in extreme cold, the constricting power of cold is evident). The fever arises because the primordial Yang Qi within the body is blocked by cold and cannot disperse, leading to increased heat. The absence of sweating and aversion to wind occur because sweat is closed by cold; the internally accumulated heat originally desires to escape via sweating, hence the aversion to wind. The wheezing occurs because the Lung Meridian of Hand-Taiyin and the Defensive Qi jointly govern the skin and hair. Cold enters the Lungs via the skin and hair, blocking the airways within the Lungs, resulting in an inability to inhale deeply and causing wheezing. However, investigating the cause of wheezing further, it is not limited to this. The chest is also a region of Taiyang. The Great Qi accumulated therein is intimately connected with the external Defensive Qi. But Great Qi is Zong Qi (Pectoral Qi); *Ling Shu* states: "Zong Qi accumulates in the chest, emerges from the throat, penetrates the heart vessels, and facilitates respiration." Since Great Qi can penetrate the heart vessels, it also circulates within the Ying Blood. In cold damage syndromes, both Ying and Wei are constrained by external cold, causing Great Qi to stagnate internally, expand, and rebel upward against the Lungs. This is another origin of wheezing.

[Mahuang Tang Formula] Ephedrae Herba (Mahuang, 麻黄) 3 liang, Cinnamomi Ramulus (Guizhi, 桂枝) 3 liang, peeled; Glycyrrhizae Radix et Rhizoma (Gancao, 甘草) 1 liang, honey-fried; Armeniacae Semen Amarum (Xingren, 杏仁) 70 seeds, peeled and removed of tips. These four ingredients are boiled in 9 sheng of water. First, boil Mahuang until reduced by 2 sheng, remove the foam on top, then add the remaining herbs and boil to obtain 2.5 sheng. Strain and take 8 ge warm (1 sheng equals 10 ge). After taking the medicine, cover with blankets to induce a slight, continuous sweating. There is no need to drink hot porridge. Rest and care instructions follow those for Guizhi Tang (Cinnamon Twig Decoction).

Mahuang has a very fierce sweating-inducing power. Boiling it first removes the floating foam because the foam contains the fierce power of releasing the exterior. Removing it serves to moderate the exterior-releasing nature of Mahuang. Mahuang is not only good at inducing sweating but also promotes urination. For exterior pathogens located in the Taiyang channel, occasionally they may enter the Fu organs and linger. (Generally, Taiyang diseases that do not resolve after many days involve the pathogen entering the Fu organs). Using Mahuang to induce sweating resolves the exterior pathogens in the channel; using Mahuang to promote urination helps dissipate pathogens that have entered the Fu organs from the channel. Moreover, Mahuang enters the Hand-Taiyin Lung Meridian to drain the Lungs and stop wheezing, ensuring that pathogens entering the Lungs via the skin and hair (which the Lungs govern) are thoroughly cleared. Thus, although not only Mahuang induces sweating in Taiyang, Zhang Zhongjing chose Mahuang exclusively for this formula. Guizhi is acrid and warm, possessing exterior-releasing power, but its action is confined to the muscle layer, making it excellent at pushing cold out from the muscles. Additionally, *Shen Nong Ben Cao Jing* states it treats upper Qi, cough, regurgitation, and inhalation-exhalation difficulties. Thus, Guizhi not only assists Mahuang in releasing the exterior but also assists in entering the Lungs to stop wheezing. Xingren is bitter and warm; *Shen Nong Ben Cao Jing* also states it treats cough and rebellious Qi, indicating its ability to assist Mahuang in stopping wheezing. Its bitter-descending nature also promotes urination, assisting Mahuang in removing lingering pathogens in the Fu organs of Taiyang, so it is added as an assistant herb. Gancao's sweet and moderating nature moderates the fierce sweating effect of Mahuang, detoxifies the slight toxicity of Xingren, and uses its earth-element property to fill the emptiness of sweat glands after sweating. With only four ingredients, the formula covers all aspects and mutually supports each other; truly, only a master could achieve this.

Appendix: Flexible Methods for Using Mahuang Tang
Human constitution shifts with the changes of Heaven and Earth's Qi. Since the Qi transformation of ancient times may differ from today, there are inevitably differences between the constitutions of ancients and modern people regarding strength, density, thinness, yin-yang bias, etc. Therefore, when applying ancient formulas today, it is appropriate to adapt them according to the times.

*Mahuang Tang* is originally used to release exterior cold. After ingestion, profuse sweating occurs, and if aversion to cold resolves, some patients recover completely. Occasionally, however, they do not recover immediately and later develop fever, transforming into a Yangming syndrome (Yangming disease). Why is this? When I first practiced medicine, I did not understand the reason. Later, I realized that after sweating following *Mahuang Tang*, if the heat trapped within the Ying and Wei returns to the surface and dissipates with sweat, the disease cures. If the heat does not return to the surface but sinks deeper, the heat will increase daily; this is the transition from Taiyang to Yangming. Having grasped this principle, when using *Mahuang Tang* now, I always add several qian of Anemarrhenae Rhizoma (Zhimu, 知母) to resolve the internally sinking heat. Treating cold damage with no sweating, this method has never failed to cure (see *Mahuang Jia Zhimu Tang* [Ephedra Plus Anemarrhena Decoction] in the Medical Formulas section for reference). *Da Qing Long Tang* (Major Green Dragon Decoction) treats cold damage with no sweating and irritability, indicating pre-existing internal heat in the chest that has no outlet, leading to depression and irritability. Therefore, Gypsum Fibrosum (Shigao, 石膏) is added to the exterior-releasing herbs to clear internal heat. However, combining Mahuang and Shigao sometimes fails to induce sweating. If using *Mahuang Jia Zhimu Tang* and adding a heavy dose of Zhimu, its cold-moistening nature combines in the Lungs to transform into sweat, reaching the exterior along with Mahuang, thereby eliminating irritability.

As discussed above, *Mahuang Tang* originally should include Zhimu. Yet occasionally, it is unsuitable, requiring careful consideration. Occasionally, patients with deficiency in the Yang aspect require the addition of Qi-tonifying herbs to *Mahuang Tang* to assist sweating.

One patient, nearly forty years old, was constitutionally frail. He contracted cold damage in late winter. The physician prescribed *Mahuang Tang*, but no sweat occurred. Seeking my consultation, his pulse seemed tight but could not withstand heavy pressure. I added Radix Astragali Preparata (Huangqi, 黄芪) and Trichosanthis Radix (Tianhuafen, 天花粉), each 5 qian, to the *Mahuang Tang*. One dose induced sweating and cured him.

Another patient, also nearly forty, had recently recovered from an initial exterior contraction. He went out to work and was re-exposed to exterior pathogens. He felt cold inside and out, had a slight headache, weak breathing, and mild chills. His pulse was imperceptible in all six positions, even under heavy pressure. I was startled but asked if he felt anything else besides coldness. Knowing he had no other distress, I deemed it treatable without unexpected risks. I added 1 liang of Huangqi to the original *Mahuang Tang*. After taking the medicine, all six pulses emerged, slight sweating occurred, and he recovered.

A third patient, over thirty years old, was constitutionally frail and addicted to opium. He contracted cold damage in winter. Being somewhat knowledgeable about medicine, he self-administered *Mahuang Tang* with no result. Upon examination, his pulse was very fine and thready, lacking a tight quality. I used the original formula, adding 5 qian of Huangqi. He sweated after taking it and recovered. These two cases illustrate situations where *Mahuang Tang* should not include Zhimu but should include Huangqi.

I once treated a young man who contracted cold damage in late winter. He had a chronic deficiency of Yin. His pulse was rapid (approaching six beats per breath), wiry, and fine. He had cold limbs, aversion to cold, and a pale white tongue coating. The attending physician noted the rapid and weak pulse and feared that despite early-stage cold damage, strong sweating with Mahuang was contraindicated. At that time, I was invited by his neighbor to consult. I said, "Although Mahuang's sweating power is fierce, using a small dose is harmless. Combined with herbs that tonify righteousness, it will surely succeed safely." I prescribed: Mahuang 1.5 qian, Guizhi tip 1 qian, Xingren and Gancao each 1.5 qian, plus Dioscoreae Hypoglaucae Rhizoma (Shanyao, 山药) and Glehniae Radix (Beishashen, 北沙参) each 6 qian. I instructed that if no sweat occurred within two hours, he should take approximately 2 fen of Aspirin to assist sweating. He followed this, sweated profusely, and recovered.

I once treated a young man surnamed Li from a neighboring village who had suffered from cold damage for ten days. The exterior syndrome had not resolved; he experienced intermittent aversion to cold, slight headache, white tongue coating, slight internal heat sensation, and yellow urine. His pulse was floating and wiry, seeming forceful under heavy pressure. This indicated heat entering the Fu organ of Taiyang (the Bladder). I prescribed *Mahuang Tang* with 8 qian of Zhimu and 6 qian of Talcum (Huashi, 滑石). One dose induced sweating and cured him.

Although this syndrome involved the exterior and Fu organ of Taiyang, it had essentially connected with Yangming. Therefore, a heavy dose of Zhimu was used to clear Yangming heat, while Mahuang was still used to release the exterior, allowing any remaining un-cleared heat to dissipate via sweat. This explains why one dose cured him. Regarding *Shanghan Lun* records of severe conditions returning to Taiyang, which should still be treated with *Mahuang Tang*, whenever I encounter such cases, I also heavily add Zhimu when using *Mahuang Tang*.

If the *Mahuang Tang* syndrome includes sore throat, reduce Guizhi by half in the formula, add 6 qian of Tianhuafen and 3 qian of Belamcandae Rhizoma (Shegan, 射干). If the throat is painful and swollen, reduce Mahuang by half, remove Guizhi, and add 3 qian of Poria Cum Radix (Shengpuhuang, 生蒲黄 - note: usually Poria is Fuling, Pu Huang is Pollen Typhae; here likely referring to Pollen Typhae for swelling) to reduce swelling. However, such modifications make cooling herbs heavy and exterior-releasing herbs light. If no sweat occurs after half an hour, take a small amount of Aspirin to assist sweating. If sweat still does not occur, continue administering Aspirin until sweating is achieved. If slight sweating covers the whole body, the throat pain and swelling will resolve.

If the *Mahuang Tang* syndrome involves a patient with a history of pulmonary consumption (lung tuberculosis/chronic wasting), add 8 qian of Shanyao and 8 qian of Asparagi Radix (Tianmendong, 天门冬) to the original formula.

If the *Mahuang Tang* syndrome involves a patient with a history of hemoptysis (coughing blood), even if cured, remove Guizhi and replace it with 2 qian of Saposhnikoviae Radix (Fangfeng, 防风) (Guizhi is strictly contraindicated in hemoptysis), and add 3 qian of Paeoniae Radix Alba (Baishao, 白芍). (Note: Ancient 1 liang approximates modern 3 qian. If dividing one decoction into three doses, each dose would contain approx. 3 qian of Mahuang). However, dosage must be carefully considered based on time, location, and individual characteristics, not rigidly fixed at 3 qian. During mild weather, sweat comes easily, so less Mahuang suffices. In severe cold, sweat is difficult to induce, requiring more Mahuang. This is adapting to the season. People south of the Yangtze River live in warm climates with thin skin; 1 qian of Mahuang suffices for sweating, hence southern medical texts often state Mahuang dosage should not exceed 1 qian. North and south of the Yellow River, 3 qian is the standard. People in Northeast China, growing up in severe cold with thick, robust skin, require more than 3 qian to induce sweating. This is adapting to geography. Regardless of north or south, or cold or warm seasons, individuals working outdoors versus those staying indoors have different skin thickness and strength, affecting ease of sweating. Dosage of Mahuang varies accordingly. This is adapting to the person. How can one use ancient formulas without flexibility?