This can be subdivided into two. One is the modification of the adjuvant drug, by which is meant subtracting some unsuitable drugs in the original prescription or adding some necessary drugs that are not in the original prescription to meet the need of treatment of present accompanying symptoms. But it should be carried out on the condition that the present chief syndrome is identical with that of the original prescription, but the accompanying symptoms are different. Since the adjuvant drug plays a minor role in a recipe, its modification is not likely to bring about a radical change of the original potency. This is also known as "the modification in the light of the symptoms".

For instance, Si Junzi Tang is chiefly designed for qi-deficiency syndrome of the spleen and stomach, marked by pale complexion, faint voice, short breath, lack of strength, poor appetite, loose stool, pale tongue with whitish fur, thready and weak pulse. It is composed of Renshen (Radix Ginseng), Baizhu (Rhizoma Atractylodis Macrocephalae), Fuling (Poria) and Zhigancao (Radix Glycyrrhizae Praeparatae), and functions to replenish qi and invigorate the spleen. If the above symptoms are accompanied by oppressed sensation over the epigastrium and abdominal distention and obstructed flow of qi, which results from dysfunction of spleen-qi, Chenpi (Pericarpiun Cirri Reticulatae) can be added to the above recipe to promote the flow of qi and relieve distention. This gives rise to another prescription entitled Yigong San.

The other refers to the modification of monarch and minister drugs or the change of the monarch drug and its compatibility by adding to or subtracting other drugs from the original prescription- Consequently radical changes will take place in terms of the potency. For example, when Guizhi (Ramulus Cinnamomi) in Mahuang Tang is substituted for Shigao (Gypsum Fibrosum ), it is called Mahuang Xingren Gancao Shigao Tang. The former takes Mahuang (Herba Ephedrae) as the monarch drug, which is combined with Guizhi (Ramulus Cinnamomi) to treat exterior-excess syndrome caused by wind-cold through inducing diaphoresis and expelling cold. While the latter take Mahuang (Herba Ephedrae ) and Shigao (Gypsum Fibrosum) together as the monarch drug to remove heat from the lung to relieve asthma.

Thereby, it is effective for curing cough with asthma due to lung-heat. It can be seen that though the two are different only in one ingredient, because of the change of the relationship between monarch drug and its compatibility, the main action of the prescription changes accordingly. In that case, the prescription for relieving exterior syndrome with pungent and warm drugs is changed consequently into one for relieving exterior syndrome with pungent and cool drugs.