How to make prescriptions with different drugs based on their rational compatibility? Besides an accurate differentiation of syndromes, establishment of therapeutic method and appropriate choice of drugs and doses, it is necessary to follow the peculiar principle of monarch (jun), minister (chen), adjuvant (zuo) and guide (shi) drugs in a prescription.

Monarch drug: Being an essential ingredient in a prescription, it plays a leading curative role aiming at the cause or the main syndrome of a disease.
Minister drug: helps strengthen the curative effect of the monarch drug.

Adjuvant drug: It refers to. ① the ingredient to cooperate with the monarch and minister drugs to strengthen the therapeutic effects or treat the accompanying diseases or syndromes; ② the ingredient to inhibit the drastic effects or toxicity of the monarch and minister drugs; ③ the ingredient to possess the properties and flavor opposite to those of the monarch drug, but play supplementing effect in the treatment when serious diseases due to excessive pathogenic factors make patients refuse the drug.

Guiding drug: It refers to ① the ingredient leading the other drugs in the prescription to the affected part; and ② the ingredient regulating the properties of other drugs in the prescription.

Take Mahuang Tang for example to explain the above principle of formulation. This recipe is composed of Mahuang (Herba Ephedrae) 9 g, Guizhi (Ramulus Cin namomi) 6 g, Xingren (Semen Armniacae Amarum) 6 g, and Gancao (Radix Glycyrrhizae) 3 g. It is used to treat exterior excess syndrome due to affection of exogenous pathogenic wind-cold, marked by aversion to cold, fever, headache, general aching, anhidrosis, asthma, thin and whitish fur, superficial and tense pulse. The syndrome herein is caused by exogenous wind-cold. Its chief syndrome is attack of wind-cold on the superficies, the accompanying one being the obstruction of the lung-qi.

Thus the therapy for expelling cold to relieve exterior syndrome and facilitating the flow of lung-qi to relieve asthma should be employed. The first two ingredients of this recipe are both pungent in flavor and warm in property, capable of expelling cold to relieve the exterior syndrome. But Mahuang (Herba Ephedrae) bears a drastic efficacy with a large dosage, and is thus used as monarch drug to deal with the cause of the disease and the chief syndrome (Ramulus Cinnamomi) helps Mahuang (Herb Epheadrae) induce sweating to disperse cold and expel exterior pathogenic factors and functions as minister drug. Xingren (Semen Armeniacae Amarum) acts as adjuvant drug with the function of descending adversely rising qi, stopping cough and relieving asthma, and is specially supposed to treat accompanying symptoms.

The last ingredient in this recipe can mediate drug properties on the one hand, belonging to a mediating drug of guiding drugs. On the other hand, it is sweet in flavor and mild in property, and can alleviate excessive diaphoretic effects induced by the first two ingredients that are pungent and warm in nature, so it is concurrently the adjuvant drug.
Here is the outline of the formulation of the above recipe:

The above principle of forming a prescription shows that drugs in a prescription have their respective importance of effect in the order of the monarch, minister, adjuvant and guiding drugs. Besides, the drugs in a recipe are related to one another -- the monarch and minister drugs cooperate with each other, the adjuvant drug coordinates or inhibits the monarch and minister drugs, ensuring the optimum effect of the recipe by means of a supplementary or opposite relationship. Moreover, not every recipe comprises invariably the monarch, minister, adjuvant and guiding drugs, nor does each of the four ingredients play a single role in a recipe. So the composition of monarch, minister, adjuvant and guiding drugs depends on therapeutic requirements.

Although monarch drug is indispensable to a recipe, it does not necessarily follow that the rest three should be included in the recipe. If the monarch drug has adequate potency, minister drug will not be included in the recipe. If the first two ingredients bear no toxic and drastic property, adjuvant drug is not needed. If the drugs meant to treat the chief syndrome can come to the affected part, no guiding drug will be involved. Some minister drugs may have the function of the adjuvant drug concurrently, so do some adjuvant drugs of the guiding drug, e.g., Gancao (Radix Glycyrrhizae) in Mahuang Tang is a guiding drug in itself, but has a concurrent function with the adjuvant drug. Therefore, this principle should never be applied mechanically.

The drugs in a prescription in accordance with the compatible principle have their special effect and action. They interact with and inhibit one another. In this way, they form an organic whole with rigorous compatibility, thereby producing significant therapeutic effect.