The central tenet of Chinese medical thought is that the whole body should be kept in harmony. The theories of yin yang and the five elements are applied to guide this practice. TCM claims that each organ of the body not only must perform well, but also must keep in balance with the rest. When one organ is not functioning, as it should, it will affect the overall performance of the others. TCM seeks to restore inner balance of the body using a method called dual modulation.
In pharmacological terms, dual modulation is when a drug (which commonly is herbal prescriptions in TCM) possesses a dual character. This means when the body is in an unbalanced state, the same drug can be used to lead the body to go from a hyper-functioning to a normal state, or from an under-functioning to a normal state, with no adverse effects. TCM application of herbs reflect these dual modulation character, and the regulating properties of the medicinal substance have categorized into eight actions; named as "ascend and descend", "cold and heat production", "yin and yang", "reinforce and reduce", "excrete/drain and astringent", "dry and moisture", "activate and stop or slow down circulation", and "dissolve and gather". The actions are exerted by carefully selecting herbs according to their properties and favors, quantity, combination, processing methods and administration method.
Four Important Aspects of Dual Modulation
Dual modulation of particular herbs and medicinal substances is possible because of four important aspects. These are:
Chinese herbs itself contains multiple active ingredients, including both acting and counter-acting ingredients;
Variation in quantity of the same herb or medicinal substance can have opposite effects on the body;
The body's adaptation ability can allow herbs to work differently in times of stress or illness;
Different preparation and combination methods can bring about different healing effects of the same herb or medicinal substance.
1. Multiple active ingredients in herbs
A single herb contains multiple active ingredients, in which the reverse-acting ingredients form the elemental basis for dual modulation actions. For herbal prescriptions that combined with several herbal ingredients can create a much more complicated mechanism. The different active ingredients can work together to produce a more desired health effect, or a particular herbal combination can cancel out the negative effects associated with a single herbal ingredient thereby minimizing side effects and retaining only the desired effect. Therefore, herbal prescriptions are combined in such a way to make them more flexible in the conditions that they treat. Western medicine simply cannot match the range and scope of Chinese herbal medicine. Some examples of this concept include:
Astragalus root (huang qi) is traditionally used for invigorating qi (vital energy), benefiting yang and general enhancement. The main active ingredients identified in this herb are astragaloside and polysaccharides. Researches have showed its dual modulation capabilities on regulating immune system. When the immune response is suppressed, astragalus root can boost it; when the immune response is too high or over functioning, astragalus root can depress it. In regarding to these results, TCM terms of invigorating qi and benefiting yang can be interpreted as promoting and regulating the body's immune functions in modern senses, a way of maintaining the balance of the internal environment.
Pseudoginseng (san qi), according to TCM application, is used to stop bleeding and activate blood as well. The ancient classic the Compendium of Materia Medica states that it can "stop bleeding, dissolve blood stasis, and relieve pain." Pharmacological research has shown that the herb has a dual action on the blood clotting system; active ingredients of pseudoginseng like saponin activates blood circulation and dissolves stasis, while dencichine stops bleeding. Other active compounds of it also possess dual effects on blood clotting. Dencichine increases the production of certain clotting factors in the liver, and activates them, helping to stop bleeding. Ginseng proponal, on the other hand, increases the cAMP content in platelets, declines the production of TXA2, and prevents thrombosis (a fixed blood clot in the body). Although the body can modulate its own coagulation-anticoagulation abilities, pseudoginseng enhances the processes significantly.
2. Variation in quantity
When using single herb or herbal prescription, different quantities will produce different health effects. For example:
Ginseng:a well-known tonic for invigorating Inborn qi, and its main ingredients are ginsenosides. Studies showed that small dosages causes high blood pressure in dogs, and also increase the strength of heart contractions. Large dosages cause hypotension (low blood pressure) temporary, decrease the strength of heart contractions and lower the heart rate.
Rhubarb (da huang):the usual dosage is 9g～15g; its main effect is promoting bowel movement, which is caused by the active ingredient quinone. However, when rhubarb is used in small dosages (around 1g), it will benefit the intestines and stop diarrhea, its active ingredient tannin takes action. This illustrates that, by using different dosages, the ratio of active ingredients that work may change, resulting in different results, a way of dual modulation.
According to some studies, dosages of astragalus root below 20g can lead to noticeable diuresis (excessive urination). However when dosages over 30g are used, it inhibits urination.
3. The body's adaptation mechanism
Recent studies showed that certain Chinese herbs such as ginseng, acanthopanax, rhodiola and reishi mushroom, codonopsis, astragalus root, schisandra, epimedium and Chinese wolfberry can improve non-specific resistance to negative influences when the body encounters harmful stimulation. This is due to the drug's enhancement of the body's own "adaptation" mechanism. This kind of non-specific resistance only works in special circumstances, such as when the body's immune resistance is low, under stress or when it has to do extra work. When the body is in normal health, therapeutic dosages of these herbs do not interfere with physiological functions or cause any adverse effects. Russian cosmonauts carried these kinds of Chinese medicines with them as health supplements during their voyage into space.
Acanthopanax
Chinese wolfberry
reishi muchroom
4. Different processing methods
Different therapeutic effects are achieved with different processing or preparation methods. For example:
Rhubarb (da huang) has a strong effect to bowel movements when used raw, the effect will become mild when processed; it can also stop bleeding after being fried. This is due to the heat that decomposes the active ingredient, quinone.
Fleece flower root (he shou wu) possesses lubricant intestines and bowel movement effects when it is used raw. When processed, it benefits the liver and kidney, replenishing the essence and the marrow. This is also due to the decomposition of the active ingredient, quinone.
Ginseng
Rhubarb
Fleece flower root
Conclusion
By understanding the dual modulation effects of single herbs on the body, you can see how it becomes even more difficult to predict how the complex interactions of several herbs in a herbal prescription will affect the body. The interactions between active ingredients contained in the herbs, dosages of each ingredient and processing methods, all contribute to make a unique remedy that can have completely different effects from a similar combination if any of these things are altered. Furthermore, the herbal remedies may react differently from person to person, due to health state or mental stress of individuals.
This is why the empirical knowledge passed down through TCM practitioners and various TCM classics is invaluable. The experiences in knowing what herbs can be combined, in what amounts, and how they should be prepared cannot be overlooked. This knowledge, combined with today's new scientific methods, help us to identify new active ingredients and understand how best to prepare and combine herbal ingredients to make even better TCM prescriptions for health maintenance.
By understanding the concept of dual modulation, you can understand why there is such variety in the efficacies of similar remedies. It is also essential to understand this concept in order that TCM prescriptions can be applied appropriately for maximum health benefits.
Reference
Tao Yufeng, What is Chinese Medicine? - A Home Companion to Chinese Medicine, Shanghai Education Publishing House 1997:102-105.
Written By:
Prof. Jiang Shufa Senior Engineer, Shanghai Institute of Materia Medica
Editors:
Angela Collingwood MSN, Integrated Chinese Medicine Holdings Ltd. Jennifer Eagleton, BA & MA (Asian Studies), Integrated Chinese Medicine Holdings Ltd. Rose Tse, Integrated Chinese Medicine Holdings Ltd.
Pseudoginseng (san qi), according to TCM application, is used to stop bleeding and activate blood as well. The ancient classic the Compendium of Materia Medica states that it can "stop bleeding, dissolve blood stasis, and relieve pain." Pharmacological research has shown that the herb has a dual action on the blood clotting system; active ingredients of pseudoginseng like saponin activates blood circulation and dissolves stasis, while dencichine stops bleeding. Other active compounds of it also possess dual effects on blood clotting. Dencichine increases the production of certain clotting factors in the liver, and activates them, helping to stop bleeding. Ginseng proponal, on the other hand, increases the cAMP content in platelets, declines the production of TXA2, and prevents thrombosis (a fixed blood clot in the body). Although the body can modulate its own coagulation-anticoagulation abilities, pseudoginseng enhances the processes significantly. 
Ginseng:a well-known tonic for invigorating Inborn qi, and its main ingredients are ginsenosides. Studies showed that small dosages causes high blood pressure in dogs, and also increase the strength of heart contractions. Large dosages cause hypotension (low blood pressure) temporary, decrease the strength of heart contractions and lower the heart rate.
