By Eric Brand

Dui yao is a concept in Chinese medicine that refers to the pairing of medicinals in clinically relevant combinations.  When we practice Chinese herbal medicine, we often draw upon groups of medicinals that accentuate each other's actions.  Many of these pairings were established in ancient formulas, and much of our modern herbal practice involves using these conceptual units in various permutations to create customized formulas that draw from ancient combinations of medicinals.  For example, Si Ni San is an ancient formula with few ingredients, but it is profound because it contains a very eloquent combination of medicinals.  Over generations, numerous other formulas have developed out of the original dui yao combinations established in formulas such as Si Ni San.

...

Si Ni San was one of the first formulas to combine several of the most prominent medicinal pairs in the history of Chinese medicine. Combinations of particular importance include Chai Hu with Bai Shao, Bai Shao with Zhi Gan Cao, and Chai Hu with Zhi Shi. Si Ni San was originally created to treat cold extremities due to depression of yang qi, but later generations expanded its use to treat disharmony of the liver and spleen. As such, Si Ni San is one of the most important base formulas for coursing the liver and supplementing the spleen.

Wood likes orderly reaching and is averse to depression. When liver qi is depressed, it is treated with acrid, dispersing medicinals such as Chai Hu, which has an upward, floating nature. The acridity of Chai Hu accounts for its strength in coursing the liver qi, but it tends to be dry and prone to damaging yin. To counteract this tendency, it is often combined with Bai Shao, which is said to emolliate (soften) the liver. Bai Shao has a blood-nourishing effect and a sour taste that is used to check the dry, out-thrusting tendency of Chai Hu. Thus, these two medicinals are often combined, and they are routinely used together in common formulas such as Chai Hu Shu Gan San (Bupleurum Liver-Coursing Powder) and Xiao Yao San (Free Wanderer Powder).

In addition, the upbearing nature of Chai Hu is paired with the downbearing medicinal Zhi Shi in the formula Si Ni San. Zhi Shi is a qi-moving medicinal that has a downward direction of movement, while Chai Hu is a qi-moving medicinal with an upward direction of movement. The combination of one upbearing with one downbearing medicinal in the formula Si Ni San is important, because these two medicinals use their complementary opposition to increase the overall movement of qi while checking each other’s extreme tendencies. Just as Chai Hu and Bai Shao combine acridity with sourness (and their corresponding dispersing and constraining natures), Chai Hu and Zhi Shi reinforce each other in the goal of moving qi.

The combination of Bai Shao with Zhi Gan Cao is also important in Si Ni San. In fact, the combination of these two medicinals constitutes a formula known as Shao Yao Gan Cao Tang (Peony and Licorice Decoction), which is a major formula for calf spasms. Bai Shao and Zhi Gan Cao are used together to treat spasmodic, cramping pain throughout the body, and they are particularly effective for cramping pain in the abdomen as well.

Si Ni San is a very useful starting point for many conditions that are due to a disharmony of wood and earth. For wood-earth disharmony manifesting in painful diarrhea, Si Ni San can be combined with the compound formula Tong Xie Yao Fang (Pain and Diarrhea Formula). In modern Chinese medicine, this combination is very common for treating patients with irritable bowel syndrome (IBS) when the case manifests with cramping pain and diarrhea due to a wood-earth disharmony.

Tong Xie Yao Fang is itself a formula for harmonizing wood and earth. Rather than using Chai Hu to course the liver, it uses the acrid nature of Fang Feng (Saposhnikoviae Radix), which is less drying. Chinese formula texts also often emphasize that Fang Feng is aromatic, which helps to guide the formula to the spleen. Tong Xie Yao Fang also contains Chen Pi (Citri Reticulatae Pericarpium) and Bai Zhu (Atractylodis Macrocephalae Rhizoma), which makes it slightly more suitable for treating spleen vacuity complicated by dampness. Tong Xie Yao Fang and Si Ni San share the presence of Bai Shao. The two formulas can be combined together, or one can simply add Chen Pi (Citri Reticulatae Pericarpium), Fang Feng (Saposhnikoviae Radix), and Bai Zhu (Atractylodis Macrocephalae Rhizoma) to Si Ni San.

To take Si Ni San in a different direction, the liver-coursing effect of Si Ni San can be strengthened by adding acrid medicinals such as Xiang Fu (Cyperi Rhizoma) and Chuan Xiong (Chuanxiong Rhizoma). These medicinals appear together in the formula Chai Hu Shu Gan San (Bupleurum Liver-Coursing Powder), which is itself an eloquent formula for treating binding depression of liver qi.

The formula Chai Hu Shu Gan San can also be expanded by adding medicinals such as Hong Hua (Carthami Flos) and Tao Ren (Persicae Semen) to combine the principles of coursing liver qi and quickening the blood. These principles are often combined because stagnation of qi tends to lead to stagnation of blood, and quickening the blood is best accomplished by simultaneously moving qi. Such modifications are particularly common in the field of gynecology, because conditions such as menstrual pain are often associated with liver depression and blood stasis.

Continuing in the direction of blood-quickening, the formula Xue Fu Zhu Yu Tang (Expelling Stasis in the House of Blood Decoction) and its own derivative formulas can be created from a base of either Si Ni San or Chai Hu Shu Gan San. This opens up an entire category of qi- and blood-moving formulas. For example, medicinals such as Pu Huang (Typhae Pollen), Wu Ling Zhi (Trogopteri Faeces), and Yan Hu Suo (Corydalis Rhizoma) can be added to relieve pain due to blood stasis, a principle also found in the formula Ge Xia Zhu Yu Tang (Infradiaphragmatic Stasis-Expelling Decoction).

In Chai Hu Shu Gan San, the liver-coursing effect of Si Ni San is accentuated. By contrast, if the spleen-fortifying aspect of Si Ni San is accentuated by the addition of medicinals such as Bai Zhu (Atractylodis Macrocephalae Rhizoma) and Fu Ling (Poria), the formula moves in the direction of Xiao Yao San (Free Wanderer Powder). Xiao Yao San is a formula that strikes a harmonious balance between coursing wood and gently supplementing earth and blood.  Further supplementation of blood with the addition of Di Huang (Rehmanniae Radix) makes the formula Hei Xiao Yao San (Black Free Wanderer Powder), while the addition of Mu Dan Pi (Moutan Radix) and Zhi Zi (Gardeniae Fructus) creates the heat-clearing, wood-earth regulating formula Jia Wei Xiao Yao San (Augmented Free Wanderer Powder).  There is beauty in all of these subtle modifications and changes, the medicinal combinations are simple yet profound.