泻火补水，润燥滑肠
辛苦寒滑。上清肺金而泻火（泻胃热、膀胱邪热、肾命相火），下润肾燥而滋阴，入二
经气分（黄柏入二经血分，故二药必相须而行）。消痰定嗽，止渴安胎（莫非清火之用）。
治伤寒烦热，蓐劳（产劳）骨蒸（退有汗之骨蒸），燥渴虚烦，久疟下痢（治嗽者，清
肺火也。治渴者，清胃热也。退骨蒸者，泻肾火也），利二便，消浮肿（小便利则肿消。东
垣曰∶热在上焦气分，结秘而渴，乃肺中伏热，不能生水，膀胱绝其化源。宜用渗湿之药，
泻火清金，滋水之化源。热在下焦血分，便闭而不渴，乃真水不足，膀胱干涸，无阴则阳无
以化。宜用黄柏、知母大苦寒之药，滋肾与膀胱之阴。而阳自化，小便自通。丹溪曰∶小便
不通，有热有湿，有气结于下，宜清、宜燥、宜升。又有隔二隔三之治∶如肺不燥，但膀胱
热，宜泻膀胱，此正治；如因肺热不能生水，则清肺，此隔二之治；如因脾湿不运而精不上
升，故肺不能生水，则燥胃健脾，此隔三之治。泻膀胱，黄柏、知母之类；清肺，车前、茯
苓之类；燥脾，二术之类。昂按∶凡病皆有隔二隔三之治，不独便闭也）。然苦寒伤胃而滑
肠，多服令人泻（李士材曰∶苦寒肃杀，非长养万物者也。世以其滋阴，施之虚损之人，则
如水益深矣，特表出以为戒）。
得酒良。上行酒浸，下行盐水拌。忌铁。
Zhi Mu (Rhizoma Anemarrhenae) clears fire and supplements water, moistens dryness and lubricates the intestines.
It is pungent, bitter, cold, and slippery in nature. Ascendingly, it clears Lung Metal to drain fire (including Stomach heat, Bladder pathogenic heat, and Ministerial Fire of Kidney and Life Gate); descendingly, it moistens Kidney dryness and nourishes Yin, entering the Qi level of these two meridians (Huang Bai enters the Blood level of these two meridians; therefore, these two herbs must be used together). It eliminates phlegm, calms cough, relieves thirst, and calms the fetus (all due to its fire-clearing effect).
It treats vexatious fever caused by Shanghan (Cold Damage), postpartum consumptive disease (Chan Lao), bone-steaming tidal fever (resolving bone-steaming with sweating), dry thirst with deficiency vexation, chronic malaria, and dysentery (treating cough involves clearing Lung fire; treating thirst involves clearing Stomach heat; resolving bone-steaming involves draining Kidney fire).
It promotes urination and defecation, and reduces edema (when urination becomes smooth, edema subsides. Li Dongyuan stated: Heat in the Upper Jiao Qi level causes constipation and thirst; this is latent heat in the Lung preventing the generation of fluids, cutting off the source of the Bladder. One should use diuretic herbs to drain fire, clear Metal, and nourish the source of water. Heat in the Lower Jiao Blood level causes constipation without thirst; this is insufficiency of True Water, leading to a dry Bladder where Yang cannot transform without Yin. One should use Huang Bai and Zhi Mu, which are greatly bitter and cold, to nourish the Yin of the Kidney and Bladder, so that Yang transforms naturally and urination flows freely. Zhu Danxi stated: Obstruction of urination may be due to heat, dampness, or Qi stagnation in the lower part; treatment should involve clearing heat, drying dampness, or raising Qi. There is also the "separated two" and "separated three" treatment methods: if the Lung is not dry but only the Bladder is hot, one should drain the Bladder directly, which is direct treatment; if the Lung heat prevents water generation, one should clear the Lung, which is separated-two treatment; if Spleen dampness fails to transport essence upward, causing the Lung to fail in generating water, one should dry dampness and strengthen the Spleen, which is separated-three treatment. To drain the Bladder, use Huang Bai and Zhi Mu; to clear the Lung, use Che Qian Zi and Fu Ling; to dry the Spleen, use Bai Zhu and Cang Zhu. Wang Ang notes: All diseases have separated-two and separated-three treatments, not just constipation.).
However, its bitter-cold nature damages the Stomach and lubricates the intestines; excessive use causes diarrhea (Li Shicai stated: Bitter-cold has a肃杀 (astringent/killing) nature and does not nurture all things. The world uses it for its yin-nourishing properties on patients with deficiency-consumption, which is like adding water to deep water; this is noted as a warning.).
It acts better when processed with wine. For ascending action, soak in wine; for descending action, stir-fry with salt water. Avoid iron.