Ingredient Mineral (矿物 kuàng wù)

Mang Xiao

Mirabilite (Glauber's salt) · 芒硝

Na₂SO₄·10H₂O (hydrated sodium sulfate, mineral mirabilite) · Natrii Sulfas

Also known as: Pò Xiāo (朴硝), Pí Xiāo (皮硝), Mǎ Yá Xiāo (马牙硝),

Mang Xiao (Mirabilite (Glauber's salt)) plant

Images shown are for educational purposes only

Máng Xiāo is a mineral salt (sodium sulfate) used as a powerful natural laxative in Chinese medicine. It works by drawing water into the intestines to soften hard, dry stools and flush out excess Heat. It is also applied externally to reduce swelling and pain from conditions like sore throats, mouth ulcers, and breast engorgement.

Category Purgatives (攻下药)
Therapeutic focus Constipation Relief Digestive Health Detoxification Swelling and Inflammation

TCM Properties

Temperature

Cold

Taste

Bitter (苦 kǔ), Salty (咸 xián)

Channels entered

Stomach, Large Intestine

Parts used

Mineral (矿物 kuàng wù)

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Educational content • Consult qualified TCM practitioners for diagnosis and treatment

What This Ingredient Does

Every ingredient has a specific set of actions — here's what Mang Xiao does in the body, explained in both everyday and TCM terms

Therapeutic focus

In practical terms, Mang Xiao is primarily used to support these areas of health:

Constipation Relief Digestive Health Detoxification Swelling and Inflammation

TCM Actions

In TCM terminology, these are the specific therapeutic actions that Mang Xiao performs to restore balance in the body:

Purges Heat and Unblocks the Bowels Softens Hardness and Moistens Dryness Clears Heat and Reduces Swelling

How these actions work

'Purges Heat and unblocks the bowels' means that Máng Xiāo draws water into the intestines through an osmotic effect, producing a strong laxative action that flushes out accumulated Heat and stagnant matter. This is its primary function and the reason it is used for severe constipation caused by excess Heat drying out the stool. It is almost always combined with Dà Huáng (rhubarb), and the two together form one of the most powerful purgative partnerships in Chinese medicine.

'Moistens Dryness and softens hardness' refers to Máng Xiāo's salty taste, which in TCM theory has the ability to soften things that have become hard and dry. In practical terms, it softens dry, compacted stool that has become rock-hard and immovable in the intestines. The salty flavour also has a natural downward-moving tendency, which aids elimination.

'Clears Fire and reduces swelling' describes Máng Xiāo's use both internally and externally for hot, swollen, painful conditions. Applied topically dissolved in water, it can reduce the swelling and pain of skin abscesses, inflamed hemorrhoids, sore throat, mouth ulcers, and red swollen eyes. It is also applied externally to the breasts to help with engorgement or weaning (stopping breastmilk production).

Patterns Addressed

In TCM, symptoms cluster into recognizable patterns of disharmony. Mang Xiao is used to help correct these specific patterns.

Why Mang Xiao addresses this pattern

Máng Xiāo directly addresses the core pathomechanism of the Yángmíng Organ pattern: excess Heat that has dried the intestinal contents into hard, immovable stool. Its cold temperature clears the intense internal Heat, its salty taste softens the hardened fecal matter ('softens hardness'), and its osmotic effect draws water into the intestines to flush everything downward. It enters the Stomach and Large Intestine channels, which are exactly the organs affected in this pattern. This is the single most important pattern for Máng Xiāo and the reason it appears in the famous Chéng Qì Tāng family of formulas.

A practitioner would look for one or more of these signs

Constipation

Severe constipation with hard, dry stool that will not move

Abdominal Pain

Abdominal fullness and pain that worsens with pressure

Fever

Tidal fever, especially worsening in the afternoon

Delirium

Delirium or confused speech from intense internal Heat

Commonly Used For

These are conditions where Mang Xiao is frequently used — but only when they arise from the specific patterns it addresses, not in all cases

Arises from: Yangming Organ (Fu) Pattern Intestinal Heat

TCM Interpretation

In TCM, constipation is not a single condition but arises from different root causes. The type of constipation that Máng Xiāo treats is specifically 'Heat-type constipation' (热秘), where excess Heat in the Stomach and Large Intestine has scorched and dried the body's fluids, leaving the intestinal contents hard, dry, and unable to move. This is an 'excess' pattern, meaning the body has too much of something (Heat) rather than too little. The person typically feels hot, may be irritable or agitated, has a red tongue with dry yellow coating, and a strong pulse. This is very different from constipation caused by weakness (Qi or Blood deficiency) or Cold, where warming and tonifying approaches are needed instead.

Why Mang Xiao Helps

Máng Xiāo is perfectly matched to Heat-type constipation because of three properties working together. First, its cold temperature directly opposes the excess Heat that is causing the problem. Second, its salty taste gives it the ability to 'soften hardness,' which means it can break down the compacted, rock-hard stool. Third, as a mineral salt (sodium sulfate), it draws water into the intestines through osmosis, providing the moisture that the Heat has depleted. This combination of cooling, softening, and moistening makes it one of the most effective substances for acute, Heat-driven constipation. It is almost always paired with Dà Huáng (rhubarb), which provides additional downward-driving force to push everything out.

Also commonly used for

Intestinal Obstruction

Used in formulas for acute simple intestinal obstruction

Abdominal Pain

Abdominal fullness, distention, and pain from accumulation

Sore Throat

Used topically (combined with borax and borneol) for pharyngitis

Mouth Ulcers

Applied topically for oral ulceration and gum swelling

Viral Conjunctivitis

Dissolved in water as an eye wash for red, swollen eyes

Hemorrhoids

External application for swollen, painful hemorrhoids

Gallstones

Used in modern clinical practice for gallstone-related abdominal pain with constipation

Ingredient Properties

Every ingredient has an inherent temperature, taste, and affinity for specific channels — these properties determine how it interacts with the body

Temperature

Cold

Taste

Bitter (苦 kǔ), Salty (咸 xián)

Channels Entered

Stomach Large Intestine

Parts Used

Mineral (矿物 kuàng wù)

Dosage & Preparation

These are general dosage guidelines for Mang Xiao — always follow your practitioner's recommendation, as dosages vary based on the formula and your individual condition

Standard dosage

6–12g

Maximum dosage

Up to 15g for severe dry constipation with Heat binding, under practitioner supervision. Higher doses risk excessive fluid loss and electrolyte disturbance.

Dosage notes

Mang Xiao is typically used at 6–12g for internal purposes. Lower doses (6–9g) provide a gentle moistening laxative effect, while higher doses (10–15g) are used for severe Heat-binding constipation with hard, dry stools. When combined with Da Huang (rhubarb) in formulas like Da Cheng Qi Tang, the synergistic effect is powerful and dosage may be kept moderate. For external use (mastitis, skin sores, hemorrhoids), an appropriate amount is dissolved in water and applied topically. Xuan Ming Fen (the weathered, anhydrous form) is milder and is preferred when a gentler action is desired, particularly for patients who are slightly weakened.

Preparation

Mang Xiao must NOT be decocted with the other herbs. It should be dissolved (冲入, chong ru) in the strained, hot decoction liquid just before drinking, or dissolved separately in hot water and taken. Boiling it with other herbs reduces its efficacy. In some formulas it is also taken as a powder (散剂) or dissolved in warm water for external application.

Processing Methods

In TCM, the same ingredient can be prepared in different ways to change its effects — here's how processing alters what Mang Xiao does

Processing method

Máng Xiāo crystals are placed in a flat-bottomed basin or wrapped in paper and hung in a well-ventilated, dry area to allow natural weathering (风化). The crystalline water gradually evaporates, leaving behind a fine white anhydrous powder (Na₂SO₄). The temperature must remain below 32°C during this process; otherwise the crystals liquefy instead of forming powder. An alternative method heats the crystals gently in a porcelain basin over a water bath until all moisture has evaporated.

How it changes properties

The temperature remains cold and the taste remains salty-bitter, but the purgative (laxative) action becomes significantly milder. The mineral is now purer anhydrous sodium sulfate. Because the osmotic laxative effect depends partly on the hydrated form, the dehydrated Xuán Míng Fěn is less effective as a purgative but retains strong Heat-clearing and swelling-reducing properties. It becomes particularly suited for topical use on mucous membranes.

When to use this form

Preferred for topical applications: mouth ulcers, throat inflammation, red swollen eyes, and skin conditions. Also used internally when a milder purgative effect is desired, or in patients who need Heat-clearing without drastic purging. It is the form used in formulas like Bīng Péng Sǎn for throat and mouth conditions.

Common Ingredient Pairs

These ingredients are traditionally combined with Mang Xiao for enhanced therapeutic effect

Da Huang
Da Huang 1:1 (e.g. Dà Huáng 9-12g : Máng Xiāo 9-12g)

The most classical pairing in Chinese medicine purgative therapy. Dà Huáng powerfully drives downward and purges Heat, while Máng Xiāo softens hardened stool and draws water into the intestines. Together they are described as 'mutually reinforcing' (xiāng xū 相须), meaning each herb dramatically amplifies the other's purgative and Heat-clearing effect. Dà Huáng provides the driving force while Máng Xiāo provides the softening and moistening.

When to use: Yángmíng Organ pattern with severe constipation, hard dry stool, abdominal fullness and pain, high fever or tidal fever, and possibly delirium. The hallmark signs are 'fullness, distention, dryness, and solidity' (痞满燥实).

Gan Sui
Gan Sui Máng Xiāo 9g : Gān Suì 1g (Gān Suì used in very small amounts due to its toxicity)

Gān Suì is a harsh water-expelling substance, and combined with Máng Xiāo it creates a powerful formula for breaking up accumulations where Heat and water are bound together. Gān Suì forcefully expels water downward while Máng Xiāo clears Heat and softens hardness. Together they address conditions where fluid and Heat have become locked together in the chest or abdomen.

When to use: Major chest bind pattern (dà xián xiōng 大陷胸) with pain in the chest and upper abdomen that worsens with pressure, hard sensation below the heart, and constipation. This is a drastic combination used only for severe acute conditions.

Zhi Shi
Zhi Shi Máng Xiāo 9-12g : Zhǐ Shí 9g

Zhǐ Shí breaks up Qi stagnation and relieves abdominal fullness and distention, while Máng Xiāo softens hardened stool and purges Heat downward. Together they address both the Qi blockage (the 'fullness' aspect) and the material obstruction (the 'hardness' aspect) in the intestines.

When to use: When constipation is accompanied by pronounced abdominal bloating, distention, and a feeling of blockage, indicating both Qi stagnation and material accumulation in the intestines.

Gan Cao
Gan Cao Máng Xiāo 9-12g : Gān Cǎo 6g

Gān Cǎo (licorice) moderates and slows down Máng Xiāo's harsh purgative action, making the combination gentler on the Stomach. This pairing transforms a drastic purge into a gentler one that still clears Heat and moves the bowels but with less risk of damaging the digestive system.

When to use: When the patient has Heat constipation but the condition is less severe, or when the patient's constitution is not robust enough for the full force of a drastic purgative. This is the core strategy of Tiáo Wèi Chéng Qì Tāng.

Key Formulas

These well-known formulas feature Mang Xiao in a prominent role

Da Cheng Qi Tang 大承氣湯 Deputy

The definitive formula showcasing Máng Xiāo's core function. In this formula, Máng Xiāo serves as Deputy to Dà Huáng, softening the hardened, dry stool (addressing 'dryness') while Dà Huáng drives everything downward (addressing 'solidity'). The formula treats severe Yángmíng Organ pattern with all four hallmark signs: fullness, distention, dryness, and solidity. Máng Xiāo is added last in the cooking process and dissolved into the strained decoction to preserve its purgative strength.

Tiao Wei Cheng Qi Tang 調胃承氣湯 Deputy

This milder formula uses only three ingredients (Dà Huáng, Máng Xiāo, and Gān Cǎo) and is called the 'gentle purgative.' Here Máng Xiāo's softening and Heat-clearing actions are moderated by licorice, making it suitable for Yángmíng Heat constipation that presents with dryness and solidity but without the severe bloating and distention that call for the full Dà Chéng Qì Tāng.

Comparable Ingredients

These ingredients have overlapping uses — here's how to tell them apart

Da Huang
Mang Xiao vs Da Huang

Both are purgative herbs used for Heat-type constipation, but they work through different mechanisms and are complementary rather than interchangeable. Dà Huáng (rhubarb) is bitter and cold, actively driving contents downward and also clearing Heat from the Blood, resolving toxins, and invigorating Blood. Máng Xiāo is salty and cold, working by softening hardness and drawing water into the intestines. Dà Huáng is the 'active mover' while Máng Xiāo is the 'softener and moistener.' When stool is extremely hard and dry, Máng Xiāo is essential because Dà Huáng alone cannot soften compacted fecal matter.

Huo Ma Ren
Mang Xiao vs Huo Ma Ren

Both treat constipation but for fundamentally different patterns. Huǒ Má Rén (hemp seed) is a mild, gentle, oily laxative that moistens the intestines for chronic constipation in elderly or weak patients with Blood or Yin Deficiency. Máng Xiāo is a powerful, drastic purgative for acute excess-Heat constipation in relatively strong patients. Huǒ Má Rén is used long-term for deficiency-type dryness; Máng Xiāo is used short-term for excess-type Heat.

Fan Xie Ye
Mang Xiao vs Fan Xie Ye

Both are strong purgatives used for constipation, but Fān Xiè Yè (senna leaf) is bitter and cold and stimulates intestinal peristalsis directly, while Máng Xiāo softens stool osmotically and is particularly suited for cases where the stool has become extremely hard and compacted. Máng Xiāo also has the additional ability to clear Fire and reduce swelling for external use, which senna lacks.

Common Substitutes & Adulterants

Related species and common adulterations to be aware of when sourcing Mang Xiao

The main confusion involves the different grades and processing forms of the same mineral: - Pu Xiao (朴硝): the crude, less-refined crystal with more impurities (MgSO4, CaCl2, etc.). It has a stronger and less predictable effect. Pu Xiao should be distinguished from refined Mang Xiao on prescriptions. - Xuan Ming Fen / Yuan Ming Fen (玄明粉/元明粉): the dehydrated, weathered powder form of Mang Xiao (anhydrous Na2SO4). It has a milder purgative effect and is considered gentler. - Pi Xiao (皮硝): the crudest grade, generally reserved for external use only. - Xiao Shi (硝石): historically confused with Mang Xiao in classical texts. Xiao Shi is actually potassium nitrate (KNO3), a completely different substance with different properties. This confusion persisted for centuries until clarified by Li Shizhen. Authentic Mang Xiao should taste salty-bitter. When dissolved in water and tested with barium chloride, it produces a white precipitate (barium sulfate) insoluble in hydrochloric acid, confirming the presence of sulfate ions.

Educational content — always consult a qualified healthcare provider or TCM practitioner before using any ingredient.

Toxicity Classification

Classical Chinese pharmacopoeia toxicity rating for Mang Xiao

Non-toxic

Mang Xiao (refined sodium sulfate decahydrate) is classified as non-toxic in the Chinese Pharmacopoeia. It is essentially a purified mineral salt. However, excessive dosage acts as a powerful osmotic laxative, drawing large amounts of water into the intestines. This can cause severe diarrhea, dehydration, and electrolyte imbalance (particularly sodium and potassium disturbances). Prolonged or excessive use may damage Spleen Yang and deplete body fluids. In healthy adults at standard dosage (6-12g), no toxic effects are expected. The traditional processing method of recrystallizing crude Pu Xiao with radish (luobo) removes impurities such as excess magnesium and calcium sulfates, producing a purer and safer product. Must be stored sealed below 30°C to prevent dehydration into thenardite powder (feng hua xiao / 风化硝).

Contraindications

Situations where Mang Xiao should not be used or requires extra caution

Avoid

Pregnancy: Mang Xiao has purgative and downward-draining properties that can stimulate uterine contractions and potentially cause miscarriage. Classical texts explicitly prohibit its use during pregnancy.

Avoid

Spleen and Stomach deficiency cold (pi wei xu han): Mang Xiao is drastically cold in nature. Using it in someone whose digestive system is already weak and cold will severely damage the Spleen Yang, worsening diarrhea, poor appetite, and abdominal pain.

Avoid

Absence of interior excess heat or dry stool: Mang Xiao is only indicated when there is genuine Heat binding with dry, hard stool. If the constipation is due to Qi deficiency, Blood deficiency, or cold, this herb will cause harm without benefit.

Caution

Active menstruation or postpartum bleeding: The herb's strong purgative and Blood-moving properties may exacerbate bleeding.

Caution

Elderly or constitutionally weak patients: The powerful draining action can deplete Qi and fluids. If use is essential, the dose should be carefully reduced and combined with tonifying herbs.

Avoid

Gastrointestinal obstruction or perforation: The osmotic laxative action could worsen an existing bowel obstruction or perforation.

Caution

Severe dehydration or electrolyte imbalance: As an osmotic purgative (sodium sulfate), Mang Xiao draws water into the intestines and can worsen fluid and electrolyte depletion.

Caution

Impaired kidney function: Sodium sulfate can place additional burden on the kidneys. Use with caution and ensure adequate hydration.

Classical Incompatibilities

Traditional Chinese pharmacological incompatibilities — herbs or substances to avoid combining with Mang Xiao

Mang Xiao appears twice in the Nineteen Mutual Fears (十九畏): 1. Liu Huang (硫黄, Sulfur) fears Pu Xiao/Mang Xiao (硫黄畏朴硝) 2. Ya Xiao/Mang Xiao fears San Leng (牙硝畏三棱, Sparganium) Additionally, the classical note from Ben Cao Jing Ji Zhu states: "Shi Wei (石韦, Pyrrosia leaf) serves as its envoy (使). It fears Mai Ju Jiang (麦句姜)."

Special Populations

Important considerations for pregnancy, breastfeeding, and pediatric use

Pregnancy

Contraindicated. Classical texts including the Pin Hui Jing Yao (《品汇精要》) explicitly state that Mang Xiao must not be used during pregnancy (妊娠不可服). As a powerful osmotic purgative, it strongly stimulates intestinal peristalsis and can induce uterine contractions. The Ben Cao Jing notes it can cause miscarriage (堕胎). While the Shang Han Lun tradition allows cautious use in life-threatening situations during pregnancy under the principle of "you gu wu yun" (有故无殒, when there is a clear pathological cause, treating it will not harm the fetus), this requires expert clinical judgment and is not a standard recommendation.

Breastfeeding

Use with caution. Mang Xiao's active component (sodium sulfate) can pass into breast milk and may cause loose stools or diarrhea in the nursing infant. Interestingly, when applied externally to the breasts, Mang Xiao (usually as Pi Xiao, the crude form) is a traditional method for promoting milk return (cessation of lactation) or treating early-stage mastitis (breast abscess), and has been clinically documented for this use. If internal use during breastfeeding is clinically necessary, the lowest effective dose should be used for the shortest possible duration, and the infant should be monitored for loose stools.

Children

Can be used in children for genuine excess Heat constipation, but the dose must be significantly reduced according to age and weight, typically one-quarter to one-half of the adult dose. Very young children and infants have immature digestive systems that are more sensitive to osmotic purgatives, so use is generally not recommended for children under 3 years. For childhood digestive accumulation (shi ji, 食积), crude Pi Xiao applied externally to the abdomen is a safer traditional method than internal use. Close monitoring for dehydration is essential in any pediatric application.

Drug Interactions

If you are taking pharmaceutical medications, be aware of these potential interactions with Mang Xiao

Reduced absorption of oral medications: As an osmotic laxative, Mang Xiao accelerates intestinal transit and can reduce the absorption of concurrently administered oral medications. Oral drugs should ideally be taken at least 1–2 hours before Mang Xiao to ensure adequate absorption. This is particularly important for medications with narrow therapeutic windows such as digoxin, warfarin, oral contraceptives, and anti-epileptics.

Diuretics and nephrotoxic drugs: Because Mang Xiao causes fluid shifts into the intestine, concurrent use with diuretics (furosemide, hydrochlorothiazide), ACE inhibitors, ARBs, or NSAIDs may increase the risk of dehydration, electrolyte imbalance, and renal impairment.

Cardiac glycosides (digoxin): Electrolyte disturbance from osmotic purging (particularly hypokalemia and hypomagnesemia) can increase sensitivity to digoxin toxicity.

Antihypertensive medications: The fluid and electrolyte shifts caused by Mang Xiao may cause unpredictable drops in blood pressure when combined with antihypertensives.

Tetracycline and fluoroquinolone antibiotics: Sodium sulfate preparations can reduce the absorption of these antibiotics.

Dietary Advice

Foods and dietary considerations when taking Mang Xiao

While taking Mang Xiao, avoid cold, raw, and greasy foods that further burden the digestive system. Drink adequate warm fluids to replenish the water drawn into the intestines by the herb's osmotic action. Avoid excessively salty foods, as Mang Xiao is itself a sodium salt. Light, easily digestible foods such as rice congee are recommended during and after use. Avoid alcohol, as it can worsen dehydration.

Botanical Description

Physical characteristics and morphology of the Mang Xiao source mineral

Mang Xiao (芒硝) is not a plant-derived herb but a mineral substance. It is the refined crystalline form of the naturally occurring mineral mirabilite, a hydrated sodium sulfate (Na2SO4·10H2O). Mirabilite belongs to the sulfate class of minerals and forms in the monoclinic crystal system. The crystals are typically colorless to white, with a vitreous (glass-like) luster, and may occasionally show pale yellowish, greenish, or bluish tints.

Mirabilite forms as an evaporite mineral in arid environments where sodium sulfate-rich brines undergo evaporation. It is commonly found along the shores of saline lakes, salt flats (playas), and around saline springs, alongside associated minerals such as halite (rock salt), gypsum, thenardite (anhydrous sodium sulfate), and epsomite. The crystals are brittle, with a hardness of only 1.5–2 on the Mohs scale, and readily lose their water of crystallization when exposed to dry air above approximately 32°C, dehydrating into a white powder known as thenardite. For medicinal use, the crude mineral (Pu Xiao, 朴硝) is dissolved in hot water, filtered, then recrystallized with radish slices to produce the purified product known as Mang Xiao.

Sourcing & Harvesting

Where Mang Xiao is sourced, when it's harvested or collected, and how to assess quality

Harvesting season

Year-round (全年均可采制). As a mineral, it can be collected in any season, though traditionally harvested from salt lake deposits during dry periods when crystallization is most abundant.

Primary growing regions

Mang Xiao (mirabilite) is a mineral, not a cultivated plant, so it is collected rather than grown. It is widely distributed across China, found in provinces including Inner Mongolia, Hebei, Shanxi, Shandong, Jiangsu, Anhui, Henan, Hubei, Sichuan, Yunnan, Guizhou, Qinghai, Xinjiang, and Shaanxi. It forms naturally in arid regions around salt lakes and saline springs. Historically, high-quality sources were noted from Yizhou (益州, roughly modern Sichuan) and the Longxi (陇西) region. In modern times, the best refined Mang Xiao comes from Sichuan and Hubei provinces, where traditional processing methods are well established.

Quality indicators

High-quality Mang Xiao should be in the form of clear, colorless or white, transparent prismatic crystals with a vitreous (glass-like) luster. The crystals should be clean, free of visible impurities or discoloration. The taste is distinctly salty and slightly bitter. Avoid product that appears dull, opaque, or has turned to white powder (indicating it has lost its crystallization water through weathering into thenardite/feng hua xiao). The best grade has large, well-formed, translucent crystals. Must be stored in sealed containers below 30°C to maintain quality.

Classical Texts

Key passages from the classical Chinese medical texts that describe Mang Xiao and its therapeutic uses

Shen Nong Ben Cao Jing (《神农本草经》)

Under the entry for Xiao Shi (消石, which classical texts note is also called Mang Xiao):

Original: 「主五藏积热，胃张闭，涤去蓄结饮食，推陈致新，除邪气。」

Translation: "It treats accumulated Heat in the five Zang organs, distension and blockage of the Stomach, washes away retained and bound food and drink, expels the old to bring in the new, and eliminates pathogenic Qi."

Ben Cao Gang Mu entry for Pu Xiao (《本草纲目》朴硝条)

Original: 「主百病，除寒热邪气，逐六府积聚，结固留癖，能化七十二种石。」

Translation: "It treats a hundred diseases, eliminates Cold-Heat pathogenic Qi, expels accumulations in the six Fu organs, dissolves hardened masses and long-standing blockages, and can transform seventy-two kinds of stones."

Yao Pin Hua Yi (《药品化义》)

Original: 「芒硝，味咸软坚，故能通燥结；性寒降下，故能去火热。」

Translation: "Mang Xiao is salty in flavor, which softens hardness, and therefore it can open Dryness binds; its nature is cold and descending, and therefore it can eliminate Fire-Heat."

Cheng Wu-Ji's commentary on the Shang Han Lun

Original: 「咸味下泄为阴...气坚者以咸软之，热盛者以寒消之，故张仲景大陷胸汤、大承气汤、调胃承气汤皆用芒硝以软坚去实热。结不至坚者，不可用也。」

Translation: "The salty flavor drains downward and belongs to Yin... What is firm in Qi can be softened by saltiness; what is exuberant in Heat can be dispersed by cold. Therefore Zhang Zhongjing used Mang Xiao in Da Xian Xiong Tang, Da Cheng Qi Tang, and Tiao Wei Cheng Qi Tang to soften hardness and eliminate excess Heat. If the binding has not reached the point of hardness, it should not be used."

Historical Context

The history and evolution of Mang Xiao's use in Chinese medicine over the centuries

Mang Xiao has one of the most complex terminological histories of any substance in the Chinese materia medica. The confusion between Xiao Shi (消石/硝石), Pu Xiao (朴硝), Mang Xiao (芒硝), and Ma Ya Xiao (马牙硝) persisted for over a thousand years. The Shen Nong Ben Cao Jing listed Xiao Shi and Pu Xiao separately but noted they were related. Tao Hongjing (陶弘景, c. 456–536 CE) commented that the Ben Jing originally had no separate entry for Mang Xiao and suspected it was identical to Xiao Shi. It was not until the Ming Dynasty that Li Shizhen, in the Ben Cao Gang Mu, clearly systematized the distinctions: Pu Xiao is the crude mineral, Mang Xiao is the purified refined crystal (named because fine needle-like "whiskers" or mang 芒 form when the solution crystallizes overnight), and Xuan Ming Fen (玄明粉) is the further weathered, anhydrous powder.

The name "Mang Xiao" literally means "crystal-whisker mineral salt" (芒 = fine needle/awn; 硝 = a type of mineral salt). In the Western world, the equivalent substance was independently recognized by the German-Dutch chemist Johann Rudolf Glauber in 1625, who named it sal mirabilis ("miraculous salt") for its laxative properties. It became widely known as "Glauber's salt."

Mang Xiao plays a central role in several of Zhang Zhongjing's most famous formulas from the Shang Han Lun and Jin Gui Yao Lue, including Da Cheng Qi Tang, Tiao Wei Cheng Qi Tang, and Da Xian Xiong Tang, where it is paired with Da Huang to soften hardness and purge excess Heat. Cheng Wu-Ji, the Song Dynasty commentator on the Shang Han Lun, emphasized that Mang Xiao should only be used when the binding has truly reached "hardness" (坚), distinguishing its role from Da Huang which merely expels fullness.