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。
知母能清泻火热、滋补阴液，润泽干燥、滑利肠道。
其味辛苦，性寒而质滑。上行可清肃肺金以清泻火热（包括胃热、膀胱邪热、肾命相火），下行可滋润肾燥以滋养阴液，主要作用于足少阴肾经和足太阳膀胱经的气分（黄柏则入这两经的血分，因此这两味药必须配合使用）。
它能消除痰饮、安定咳嗽，止渴并安胎（这主要是清泻火热的作用）。
用于治疗伤寒引起的烦热、产后虚劳（产劳）、骨蒸潮热（退除有汗的骨蒸症状）、因燥热引起的口渴和虚烦、久疟疾以及下痢（治疗咳嗽是因为清肺火；治疗口渴是因为清胃热；退除骨蒸是因为泻肾火）。
它能通利大小便，消除浮肿（小便通畅则浮肿消退。李东垣说：热邪在上焦气分，导致便秘且口渴，这是肺中有潜伏的热邪，不能化生阴液上承，导致膀胱失去化源。应当使用渗湿的药物，清泻火热、清肃肺金，以滋补水液的化源。若热邪在下焦血分，导致便秘但不口渴，这是真阴不足，膀胱干涸，无阴则阳气无法化生。应当使用黄柏、知母这类大苦大寒的药物，滋养肾与膀胱的阴液，这样阳气自然化生，小便自然通畅。朱丹溪说：小便不通，有因热、有因湿、有因气结于下部，应当清热、燥湿或升提。还有“隔二”、“隔三”的治疗法：如肺不燥，仅是膀胱热，应直接泻膀胱，这是正治；如果因肺热不能生水，则清肺，这是隔二之治；如果因脾湿不运导致精气不能上升，进而肺不能生水，则燥湿健脾，这是隔三之治。泻膀胱用黄柏、知母之类；清肺用车前子、茯苓之类；燥脾用苍术、白术之类。汪昂按语：凡是疾病都有隔二隔三的治疗法，不仅仅局限于便秘）。
然而，苦寒之性容易损伤胃气并滑肠，多服用会导致腹泻（李士材说：苦寒具有肃杀之气，不是长养万物的性质。世人因为它能滋阴，就将其用于虚损之人，这就如同水越加越深了，特此提出以作警戒）。
酒制后效果更佳。上行时需用酒浸泡，下行时需用盐水拌炒。忌与铁器接触。
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.