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(Cattail Pollen / Zexie) Drains damp-heat from the Qi aspect of the Bladder.
Ze Xie (Zexiae Rhizoma, specifically enters the Bladder and Kidney meridians). Sweet, bland, slightly cold. It can enter the Qi aspect of the Bladder to drain fire pathogens from the Kidney meridian. Its efficacy specializes in promoting urination and removing dampness. Therefore, it is used in Wu Ling San (Five Ingredient Powder with Poria).
It also treats conditions where water accumulation causes irritability and thirst, difficult urination, or vomiting or diarrhea; Wu Ling San is the primary formula. The use of Ze Xie in the formula indicates its proficiency in moving water. (Ba Wei Wan [Eight-Ingredient Pill] uses this herb to drain damp-fire from the Kidney meridian.)
Li Shizhen said: In Di Huang Wan [Rehmannia Pill], Fuling (Poria) and Ze Xie are used to drain pathogenic qi from the Bladder, not to guide tonification. Ancients, when using tonifying medicines, always combined them with draining herbs. Once pathogens are removed, tonics can take effect. One opening and one closing constitutes the profound mystery. Later generations did not understand this principle, focusing solely on tonification, thus long-term use inevitably leads to harm from excessiveness.
Wang Ang said: Liu Wei Di Huang Wan contains the warmth of Shu Di Huang (Prepared Rehmannia Root), the coolness of Mu Dan Pi (Moutan Cortex), astringency of Shan Yao (Dioscorea Rhizome), permeability of Fu Ling (Poria), astringency of Shan Zhu Yu (Cornus Fruit), and draining action of Ze Xie. It tonifies the Kidney while simultaneously tonifying the Spleen. There must be draining accompanying tonification; they harmonize and assist each other to achieve balanced tonification. This is the miracle within simplicity, making it an unchanging excellent prescription since ancient times. Even with modifications, such as adding one Zi He Che (Human Placenta), or a few flavors like Wu Wei Zi (Schisandra Berry), Mai Dong (Ophiopogon Tuber), Du Zhong (Eucommia Bark), or Niu Xi (Achyranthes Root), it rarely exceeds two or three ingredients. Modern people doubt the draining nature of Ze Xie and remove it, arbitrarily adding many tonifying herbs from materia medica. With tonification but no draining, and guest herbs outnumbering host herbs, responsibility is not focused, causing the efficacy of Liu Wei Wan to retreat to a vacant position, losing the original intent of the prescription. This is the error of mediocre physicians in recent times.
(Thus) ensuring tonification does not become excessive allows for safe tonification. How can one say Ze Xie tonifies Yin with efficacy comparable to Di Huang (Rehmannia)? However, if damp-heat is not eliminated, symptoms become unpredictable, leading to conditions such as Xiao Ke (Wasting-Thirst), vomiting, Tan Yin (Phlegm-Fluid retention), swelling, Hong Kong Jiao (Tinea Pedis/Foot Athlete's Foot), Yin Han (Scrotal Sweating), Hematuria, and Jing Xie (Spermatorrhea). (These symptoms are all caused by the harm of damp-heat.) Using this herb's sweet, bland, and slightly salty properties facilitates percolation and drainage. (How can spermatorrhea be treated with diuretics? Because it arises from damp-heat, diuretics are necessarily employed.) Thus, turbid Qi descends, and clear Qi ascends. (Hence, there is the efficacy of clear hearing and bright vision.) It is said that eliminating one cause eliminates hundred diseases. But if urination is excessively profuse, Kidney Water becomes more deficient, and vision will surely dim. (Yi Lao said: Draining hidden water and removing retained filth clarifies the eyes; excessive urination depletes Kidney Qi, causing dim vision.) This is a fixed principle. Stir-fry with salt water, or mix with wine. Avoid iron.