Tangji is one of the dosage forms of medicine, also known as decoction. It is made by boiling the medicine, removing the residue and extracting the medicinal juice. Tangji has the advantages of fast absorption and strong effect, hence the saying "Tang, wash away." It can also be flexibly prescribed according to specific clinical symptoms, making it the most widely used in clinical practice. The "Sheng Ji Jing" states: "The main treatment of the decoction lies in the follicles. For all those who need to eliminate evil qi, the decoction is most suitable. In the treatment of typhoid fever, the decoction is often used first." The preface of the "Qian Jin Yao Fang" states: "All ancient prescriptions for treating diseases are based on the decoction method, and there is not a single one that uses powders… For sudden and severe diseases caused by evil spirits, the decoction is necessary for washing and cleansing."
In fact, the process of decocting Chinese herbs is the continuous release and dissolution of the active ingredients in the Chinese herbal pieces. When the concentration of the active ingredients in the herbal pieces and the medicinal liquid reaches equilibrium, this diffusion movement stops. If the decoction continues in order to achieve "more concentrated and less in volume", not only will the active ingredients in the medicine not be released again, but non-active ingredients (such as resins, gums, pigments, etc.) may continue to dissolve. This will reduce the concentration of active ingredients in the medicinal liquid due to evaporation, and may even be destroyed by prolonged high temperatures, thereby reducing the efficacy of the medicine.
In addition, prolonged decoction can also cause the decoction to become turbid. Overly concentrated decoction will increase the bitterness, making it difficult for patients to take the medicine, and may cause side effects such as nausea and vomiting after taking the medicine. Therefore, in order to ensure the effectiveness of Chinese medicine, it is necessary to decoct for a certain period of time according to the nature of the medicine. In most cases, it is advisable to decoct twice for various types of decoctions. After the decoction is done, it should be filtered while hot and squeezed dry to minimize the residual amount of the decoction in the herbal residue.
For drugs containing volatile components, such as peppermint, perilla leaf, patchouli, etc., they do not need to be decocted for a long time. They are generally added later during the decoction process, and the lid should be covered to prevent the loss of active ingredients. For heat-clearing drugs such as honeysuckle and chrysanthemum, as well as aromatic drugs such as Amomum villosum and sandalwood, they also do not need to be decocted for a long time. Some tonifying drugs require concentrated decoction, but the specific degree of decoction and the amount used should be determined by a traditional Chinese medicine physician based on the condition, and it is not appropriate to increase the dosage or prolong the decoction time without authorization. Some Chinese medicines containing saponins, such as sand ginseng, Tianqi, Achyranthes, licorice, and Platycodon grandiflorum, will start to boil before the temperature reaches 100℃, resulting in a "false boiling" phenomenon. If the medicine is taken off the heat at this time, the active ingredients in the herbs will not dissolve sufficiently, and the efficacy will be affected, resulting in an unexpected therapeutic effect. Therefore, attention should be paid to the decoction process.
Therefore, it is important to note that the decoction time of Chinese medicine should follow the doctor's instructions and vary depending on the type of medicine and the nature of the disease. Longer decoction time does not necessarily mean better efficacy.
