Gui Zhi Tang is the first formula described in the Shanghan Lun, and the most diverse. It is repeatedly mentioned in the text in relation to different clinical applications. It is often associated with the tai yang classification of disease, linking it to diseases of external pathogenic wind manifesting in fever, chills, body aches and spontaneous sweating. However it is also mentioned in correlation to tai yin and jue yin diseases for situations which involve internal disorders of blood and qi disharmony manifesting in symptoms such as aversion to cold, spontaneous sweating, chronic muscular tension and pain (including skeletal smooth and cardiac muscles).  

In order to properly use this formula it is necessary to understand its underlying mechanism of action which is harmonizing the functions of ying qi and wei qi. This is explained in line 53 of the Shanghan Lun:

以营行脉中，卫行脉外，复发其汗，营卫和則愈，宜桂枝汤

“By means of ying circulating in the vessels [and] wei circulating outside of the vessels, restore the generation of the sweat, [when] ying and wei harmonize then there is healing, it is proper [to use] gui zhi tang.”

Ying qi & Wei qi

What is the meaning of disharmony of ying and wei? How does this affect the function of the body?

Ying qi is often translated as ‘nutritive qi’. It refers to the yin quality of the body’s immune function and rehabilitation processes, including the substances and fluids that nourish and restore the organs and tissue. Due to its yin quality and function it circulates within the body through vessels allowing it to maintain structure and stability. 

Wei qi is often translated as ‘defense qi’. It refers to the yang quality of the body’s defense mechanisms and mobility. Due to its yang quality and function its circulation is not inhibited by vessels allowing it to be agile, attentive and responsive to changing circumstances. When they work together in harmony the body is resilient and can deal with challenges. When they are disharmonious the body is exposed and vulnerable to harm both externally and internally.

The Shanghan Lun provides a descriptive explanation of the underlying mechanism of this disorder in line 12:

“In greater tai yang wind strike with floating yang and weak yin, floating yang is spontaneous heat effusion, and weak yin is spontaneous issue of sweat. If there is huddled aversion to cold, wetted aversion to wind, feather warm heat effusion, noisy nose, and dry retching, gui zhi tang governs.”

Translated by Craig, Feng & Weisman

“Floating yang with weak yin”: this describes both the quality of the pulse as well as the underlying mechanism of this disorder.

• The pulse: a floating yang pulse is superficial felt with light pressure and disappears with heavier pressure. This pulse is associated with the body’s reaction to an external pathogenic invasion. The wei qi is driven to the surface of the body to battle an offensive force.

• Disease mechanism: The floating yang refers to stimulation of the wei qi at the surface, which in this case is a reaction to a pathogenic influence. The focus of the wei qi on external stimuli causes the ying qi to be less protected and therefore exposed and relatively weakened. This in itself is a normal and healthy reaction to a perceived threat to the body. However, when the ying and wei are not harmonized, this reaction leads to non-productive results.

“Weak yin is spontaneous issue of sweat”: This does not indicate a state of yin deficiency or even ying deficiency. This is a situation where the ying qi follows the wei qi and moves toward the exterior.  In a healthy situation the ying qi and wei qi work together and produce a sweating reaction that is used to expel the pathogen from the body. In this case all that is produced is unregulated sweat, causing a loss of ying qi that lacks the force to expel the harmful influence.

Lines 53 and 54 of the text describe a similar situation of spontaneous sweating without the involvement of an external pathogen. This indicates that this pathological reaction can be instigated by other environmental stimuli. We can see for example psychological stressors as instigators of this sort of response as well.

The passage then gives examples of three symptoms which can be viewed as representing manifestations of the disease mechanism, all of which reflect an imbalanced wei qi response:

1. “Huddled aversion to cold”: one of the functions of the wei qi is to warm the body. In this case when the wei qi rushes to the exterior it neglects this function and the body reacts by attempting to stay warm by curling up. This is a muscular reaction of tensing and contracting which is characteristic of this syndrome.  
2. “Wetted aversion to wind”: This describes the feeling of chills when we are exposed to wind while we are wet, leading to the need to cover ourselves with a towel or additional clothing. This reflects the sense of vulnerability our body experiences when the wei qi is preoccupied with an external stimuli and does not provide sufficient overall protection. This symptom can be associated with goose bumps which are not only a response to cold but also a response to a feeling of being overly exposed.
3. “Feather warm heat effusion”: this describes a sensation of fever which is not intense and overbearing but causes a sense of discomfort. This heat is reflective of the battle between the wei qi and the pathogen. The pathogen incites a reaction from the wei qi, but it is flimsy and inefficient.

Ingredients

The five ingredients of the formula are well-suited to restore harmony between ying and wei. This is a gentle yet sophisticated formula that has several layers of synergy between the herbs:

• Gui zhi and sheng jiang: Acrid and diaphoretic herbs that stimulate the yang and support the functions of wei.
• Shao yao, da zao and zhi gan cao: Astringent and sweet herbs that embrace the functions of ying.
• The harmonizing action of zhi gan cao promotes balance between the two forces.
• The synergetic combination of gui zhi and shao yao support the function of ying and wei on the exterior; promote circulation of fluid, blood and qi; and relax muscle tension.
• The synergetic combination of sheng jiang, da zao and zhi gan cao supports the functions of the stomach and spleen to promote and regulate the production of ying and wei.

These five herbs create a harmonizing effect that restores the body’s ability to protect and nourish while responding to the external environment.  

Instructions for administration

After taking the formula it is advised to eat 200 ml of warm rice porridge. This enhances the functions of both wei and ying, encouraging them to respond to the herbs and provides substance for renewal of production of both qi and fluids.

While taking the formula, it is advised to refrain from eating difficult to digest foods such as dairy, fresh vegetables, and fatty food; and also avoid heating foods such as hot spices, alcohol, and fried food. It is also recommended to cover up after taking the herbs to stimulate a gentle sweating response.

Unfavorable side effects

It is always important to observe the patient’s reaction to a formula to determine if this is the appropriate treatment. In the case of gui zhi tang the text provides two warning signs that the formula should be stopped:

1. This formula is meant to create a gentle sweating, often just a slight sensation of moistness on the skin. If the body reacts in profuse sweating the formula should be discontinued and differential diagnosis should be made. According to the text this indicates there might be an underlying yang deficiency that was overlooked. 
   
2. The symptoms of the formula include slight heat that can manifest as feverishness redness on the skin, or hypersensitivity in general. However, this heat is a result of the stimulation of wei qi on the surface, it is not a result of either excess or deficient heat syndromes. In case of true heat gui zhi tang should not be given. If the patient reacts to the formula by intensified heat symptoms this indicates the condition was misdiagnosed and another formula addressing the heat should be given.

Summary

Line 12 which we have now analyzed refers to a tai yang disease when an external influence triggers a pathological response due to the disharmony of ying and wei. In this case the symptoms reflect the external pathogenic influence. When the manifestation of this disharmony is triggered by another cause, the symptoms can differ, but the mechanism is the same. For example over-sensitivity of the senses. This is due to excessive activity of wei qi at the surface leading to over-sensitivity to external sensual stimulation with a sense of vulnerability and unease. This can be observed in conditions of extremely light sleep when every slight noise or change in light can disrupt. This can also apply to conditions of hormonal imbalance such as sensitivity to smell in the first weeks of pregnancy.

This analysis of gui zhi tang demonstrates a general guideline to the reading of the Shanghan Lun and is summed up in the famous saying:

抓病机，活用经方
“Grasp the mechanism of disease, to flexibly apply the formulas “