Source 出处 · Wenbing Tiaobian · Doses are not given here: they are set by a licensed practitioner for the individual.
Safety. Yi Wei Tang is recorded in the Wenbing Tiaobian for the stage after a febrile illness has passed its peak: the heat has receded, the fluids are damaged, and what is left is a person with a dry mouth, a dry red tongue with little coating, and — in the phrase the text uses — 不饥不食, neither hungry nor eating. The composition answers that description directly: three sweet, moistening roots, one rhizome, and crystal sugar.
The honest modern framing is that 不饥不食 is not a pattern to be tonified but a symptom to be explained. Loss of appetite that persists after an illness, especially with weight going down, is an indication for investigation in every clinical guidance set: unresolved or smouldering infection including tuberculosis, malignancy, iron-deficiency anaemia, thyroid disease, depression, uraemia and liver disease, medication effects, and in older people the simple downward spiral of deconditioning and sarcopenia. The second half of the picture matters too. Dry mouth and thirst are produced by a long list of ordinary things — anticholinergic medicines, antihistamines, some antidepressants and antipsychotics, diuretics, opioids, uncontrolled diabetes, radiotherapy or surgery involving the salivary glands, mouth breathing from nasal obstruction or sleep apnoea, dehydration, and anxiety. Dry mouth with thirst and weight loss is, before anything else, a reason to check blood glucose.
Identity is the other half of what is worth saying. 沙参 is one name for two unrelated plants: 北沙参 is the root of Glehnia littoralis, a salt-tolerant coastal plant in the carrot family, while 南沙参 comes from Adenophora species in the bellflower family. Classical texts use the word without specifying, and the two are not interchangeable as botanicals. 麦冬 is likewise admitted from two species under the Chinese Pharmacopoeia, Ophiopogon japonicus and Liriope spicata (山麦冬). 生地 is unprocessed Rehmannia glutinosa root, and it is a different substance from 熟地, the processed form — the pairing shows up in other entries in this library precisely because the difference is real. 玉竹 is Polygonatum odoratum, which is not 黄精 (Polygonatum sibiricum and relatives); same genus, different species, different traditional use.
One composition fact deserves to be stated without softening: 冰糖 is sugar. A bowl of this decoction carries a genuine sugar load, and the person described in the classical line — recovering, thin, not eating — is often exactly the person whose blood glucose has not yet been checked.
This entry records how a classical text handled a convalescent state. It is not a substitute for finding out why someone is not eating.
益胃汤著录于《温病条辨》，用于热病高峰已过之后的那一段：热退了，津液伤了，留下的是一个口中干燥、舌干红少苔、按原文的说法「不饥不食」的人。组成正是照着这个描述配的：三味甘润的根、一味根茎，再加冰糖。
老实说，「不饥不食」不是一个可以进补的证，而是一个需要解释的症状。**病后持续食欲不振**，尤其伴体重下降，在各国的临床指引里都是**检查指征**而不是调补指征：未清的或迁延的感染（含结核）、肿瘤、缺铁性贫血、甲状腺疾病、抑郁、尿毒症与肝病、药物影响，以及老年人单纯的失用性衰退与肌少症。另一半同样要讲：**口干与口渴**由一长串很平常的原因造成 —— 抗胆碱药、抗组胺药、部分抗抑郁与抗精神病药、利尿剂、阿片类、未控制的糖尿病、涉及唾液腺的放疗或手术、因鼻塞或睡眠呼吸暂停而张口呼吸、脱水，以及焦虑。**口干＋口渴＋体重下降，首先要做的是查血糖。**
辨物是另一半要说的话。**沙参**这一个名字对应两种毫不相干的植物：**北沙参**是伞形科珊瑚菜（生于海边、耐盐）的根，**南沙参**则是桔梗科沙参属的根；古典文献用这个词时未作区分，而作为植物药两者不能互替。**麦冬**在中国药典里同样收两个来源：麦冬与**山麦冬**。**生地**是玄参科地黄的根、未经炮制，与炮制过的**熟地**是两物 —— 本库另有条目正因这个差别而并列两味，差别是实在的。**玉竹**是玉竹，不是**黄精**，同属不同种、传统用途也不同。
组成里还有一件事不该含糊：**冰糖就是糖**。这一碗汤带着一次真实的糖负荷，而古典条文描述的那个病后消瘦、不想吃东西的人，往往正是还没查过血糖的那个人。
本条是「古典文献如何处理病后调理」的一份记录。它不能替代去查明一个人为什么吃不下东西。