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Single-herb prescriptions (Danfang) refer to formulas containing no more than one or two herbs, treating no more than one or two symptoms, yet their efficacy is remarkably rapid. If used inappropriately, they can also harm the body; this is what the world calls "Zhangshangfang" (prescriptions with exaggerated claims of efficacy). Their origin lies in Bencao (Materia Medica). Generally, ancient sages, when distinguishing the properties of medicinal substances, would necessarily record their functions, such as expelling wind (Zhufeng), dispelling cold (Zhuhan), resolving toxicity (Jiedu), and relieving pain (Dingtong). Whenever a patient suffers from a condition with only one or two primary manifestations, a single herb is used for treatment. Because the prescription is specialized, its therapeutic force is concentrated, naturally yielding miraculous effects. However, if a disease involves multiple symptoms, several herbs must be combined to form a formula. In later generations, as the number of medicinal substances increased daily, so did the number of single-herb prescriptions, resulting in some being effective and others ineffective. Regarding external pathogens and internal injuries, there are inherent laws of transmission and transformation, distinctions between deficiency (Xu) and excess (Shi), differences in duration (acute vs. chronic), and variations in depth of pathology. Furthermore, human constitutions vary, and climatic conditions differ. These complexities cannot be treated by those who do not adhere to fundamental principles while exercising flexibility (Shoujing daquan). If single-herb prescriptions were used universally, the specific nature of the herbs would lack regulation, leading to biased but impure actions, where benefits inevitably bring harms. Therefore, physicians should not experiment with them casually; this is why Jingfang (Classic Prescriptions) are so highly valued. Nevertheless, consulting single-herb prescriptions broadens knowledge and serves as a reserve for emergency situations; or as methods for targeted attack on pathogenic factors, this is also knowledge that cannot be ignored.

Heaven and Earth possess the virtue of loving life, and sages possess a heart of great impartiality. Creating formulas to treat diseases and making them known to all under heaven—could this not be the greatest wish of Heaven, Earth, and the Sages? By comparing the superiority and inferiority of formulas to assess efficacy, some cures the disease while others cause harm; changes are unpredictable. This represents the method of great impartiality. As for Jin Fang (Forbidden Prescriptions), their meanings may be unclear, and their mechanisms unfathomable. Their transmission often comes from eccentric hermits, or even immortals, Buddhas, ghosts, and gods. Encountering them is difficult, hence they are cherished intensely. If given away lightly, people would develop a casual attitude, which is why practitioners often guard them closely; this is human nature. On one hand, it is feared that the secrets of Heaven and Earth might be revealed. The preparation methods of herbs in forbidden prescriptions are invariably unique, and their combinations ingenious, exhausting the principles of Yin and Yang (Yin-Yang) and peering into the mechanisms of creation. Their compounding requires utmost sincerity, reverence, and caution; any violation of taboos renders the medicine unverified. If shown to others lightly, the vital energy (Qi) leaks, and the efficacy becomes ineffectual; this is again the principle of Yin and Yang. The *Lingshu* (Spiritual Pivot), chapter *Jinfu*, records: Huangdi (Yellow Emperor) said to Leigong, "This was prohibited by former masters, obtained through an oath of cutting arms and drinking blood." Thus, Huangdi had the Lantai Cang (Lantai Treasury), Changsang Jun had warnings against leakage, and ancient sages acted similarly. As for deceitful individuals seeking profit, they falsely claim "forbidden prescriptions" to deceive the public. Worse still, some cultivate hot-natured drugs to induce lust under the guise of health preservation, actually accelerating death. This is a vicious habit of the Jianghu (unorthodox medical circles), which sages condemn. There are also ancient forbidden prescriptions that have spread widely, recorded in medical texts alongside classic prescriptions; those with insight will naturally select appropriately.