Sang Bai Pi (桑白皮): The Lung-Draining Herb for Cough and Edema

Introduction: The Premier Herb for Lung Heat and Water Swelling

Sang Bai Pi (桑白皮), or Mulberry Root Bark, occupies a unique position in the Chinese materia medica as the primary herb for draining Lung heat while simultaneously promoting urination to reduce edema. Derived from the root bark of the mulberry tree (Morus alba L.), this herb bridges two seemingly distinct clinical domains — respiratory complaints and fluid retention — through the TCM understanding of the Lung’s dual physiological roles.

In classical texts, Sang Bai Pi is described as having a “descending” nature that guides heat and fluid downward, making it indispensable for patterns where Lung heat causes cough and wheezing, or where impaired Lung function leads to water swelling.

Properties and Channel Entry

Property	Detail
Pinyin	Sang Bai Pi
Chinese	桑白皮
English	Mulberry Root Bark
Nature	Cold (寒)
Flavor	Sweet (甘)
Channel Entry	Lung (肺经)

Sang Bai Pi’s sweet flavor allows it to gently nourish without being harsh, while its cold nature enables it to clear heat. Its exclusive entry into the Lung channel makes it a highly targeted herb — its effects concentrate precisely where they are most needed for both respiratory and fluid-regulation disorders.

Key Functions

1. Drain Lung Heat and Stop Cough and Wheezing

Sang Bai Pi excels at clearing Lung heat and descending Lung Qi to relieve cough and wheezing. When heat accumulates in the Lung, it causes Qi to rebel upward, producing:

• Cough with yellow or sticky sputum
• Wheezing (喘) and dyspnea
• Rapid breathing and a sensation of chest fullness

By draining heat downward and restoring the Lung’s natural descending function, Sang Bai Pi addresses both the root (heat) and the manifestation (rebellious Qi).

2. Promote Urination and Reduce Edema

Sang Bai Pi is equally valued for its ability to promote urination and reduce swelling (利水消肿). It is particularly effective for:

• Facial edema (面浮肿) — often the first sign of water accumulation
• Body edema with reduced urination
• Ascites when due to Lung Qi failing to regulate water passages

The Lung’s Dual Role: Why One Herb Treats Both

Understanding Sang Bai Pi’s versatility requires appreciating the dual function of the Lung in TCM physiology:

1. The Lung governs Qi (肺主气) — It controls respiration and the movement of Qi throughout the body. When Lung heat causes Qi to rebel upward, cough and wheezing result.

2. The Lung regulates the water passages (肺主通调水道) — The Lung is the “upper source of water” (肺为水之上源). By descending and disseminating Qi, the Lung regulates how water moves through the body. When Lung Qi fails to descend, water accumulates and causes edema.

Sang Bai Pi’s genius lies in addressing both aspects simultaneously: by draining Lung heat and restoring the descending function of Lung Qi, it stops cough (the Qi-regulation problem) and reduces edema (the water-regulation problem). This dual action makes it irreplaceable in clinical practice.

Clinical Applications

Lung Heat Cough with Yellow Sputum

For cough due to Lung heat marked by yellow, sticky sputum, thirst, and a rapid pulse, Sang Bai Pi clears heat and descends Qi. It is often combined with:

• Huang Qin (黄芩) — for stronger heat-clearing
• Zhe Bei Mu (浙贝母) — for heat-phlegm
• Xing Ren (杏仁) — to assist Qi descent and stop cough

Wheezing and Dyspnea

For wheezing with a sensation of heat in the chest, Sang Bai Pi is the herb of choice. It descends Lung Qi and drains heat from the respiratory tract, providing relief from both the wheezing sound and the sensation of chest oppression.

Facial and Body Edema

For edema that begins in the face (a hallmark of Lung-related edema) and spreads to the body, Sang Bai Pi opens the water passages from above. This approach reflects the TCM principle: “To treat lower body edema, treat from above” — restoring the Lung’s regulatory function allows water to drain naturally.

Hypertension

In modern TCM practice, Sang Bai Pi has been applied for hypertension, particularly when the pattern involves Liver yang rising with underlying Lung heat. Its mild hypotensive effect has been validated by pharmacological research.

Famous Formulas Featuring Sang Bai Pi

Xie Bai San (泻白散) — The Signature Formula

Xie Bai San is the most important formula featuring Sang Bai Pi and the one most clinicians associate with this herb. Originating from the Xiao Er Yao Zheng Zhi Jue (Key to Therapeutics of Children’s Diseases) by Qian Yi (钱乙), it is the classic formula for Lung heat with cough.

Ingredient	Role
Sang Bai Pi (桑白皮)	Chief herb — drains Lung heat, descends Qi, stops cough
Di Gu Pi (地骨皮) — Wolfberry Root Bark	Clears Lung heat at the blood level, reduces steaming bone
Zhi Gan Cao (炙甘草) — Honey-fried Licorice	Harmonizes, protects the Spleen, moistens the Lung

The combination of Sang Bai Pi and Di Gu Pi is particularly elegant: Sang Bai Pi drains heat from the Qi level, while Di Gu Pi clears heat from the blood level, ensuring that Lung heat is addressed comprehensively. Zhi Gan Cao both harmonizes the formula and prevents the cold herbs from damaging the Spleen.

Xie Bai San is indicated for: cough with rapid breathing, fever, and a red tongue with yellow coating — the classic presentation of Lung heat.

Sang Bai Pi Tang (桑白皮汤)

This formula combines Sang Bai Pi with additional heat-clearing and phlegm-resolving herbs for more severe Lung heat with thick phlegm. It typically includes Huang Qin, Zhe Bei Mu, and Xing Ren alongside Sang Bai Pi as the chief ingredient.

Wu Pi San (五皮散) — The Five-Bark Formula for Edema

Wu Pi San uses five herb barks to treat edema, with Sang Bai Pi representing the Lung’s role in water regulation:

• Sang Bai Pi (桑白皮) — drains Lung heat, opens water passages from above
• Chen Pi (陈皮) — moves Qi, dries dampness
• Da Fu Pi (大腹皮) — promotes movement of Qi, reduces swelling
• Sheng Jiang Pi (生姜皮) — promotes sweating, reduces surface edema
• Fu Ling Pi (茯苓皮) — drains dampness, promotes urination

The inclusion of Sang Bai Pi ensures that the Lung — the upper source of water — is addressed alongside the Spleen and other organs involved in fluid metabolism.

The Mulberry Tree: A TCM Pharmacy in One Tree

The mulberry tree (Morus alba) is one of the most medicinally productive plants in TCM, with virtually every part used as medicine:

Part	Herb Name	Primary Function
Leaf	Sang Ye (桑叶)	Disperses Wind-Heat, clears Lung heat, cools blood
Root bark	Sang Bai Pi (桑白皮)	Drains Lung heat, reduces edema
Twig	Sang Zhi (桑枝)	Dispels Wind-Damp, unblocks channels
Fruit	Sang Shen (桑椹)	Nourishes Yin, enriches blood

This remarkable versatility reflects the TCM principle that different parts of a single plant embody different energetic properties, making the mulberry tree a “living pharmacy” in the tradition.

Preparation: Honey-Fried vs. Raw

The preparation method for Sang Bai Pi significantly alters its clinical emphasis:

• Honey-fried (蜜炙桑白皮): The honey-frying process enhances the herb’s moistening and cough-stopping properties. It is preferred for Lung heat cough and wheezing, as the honey softens the cold nature slightly while directing the herb’s action to the Lung.

• Raw (生桑白皮): The raw herb retains a stronger diuretic and edema-reducing effect. It is preferred when the primary concern is water swelling and reduced urination, where the draining action needs to be more forceful.

This distinction exemplifies the TCM practice of pao zhi (炮制) — processing herbs to modify their therapeutic direction.

Dosage and Precautions

Parameter	Detail
Standard dosage	6–15 g in decoction
Honey-fried	Use toward the higher range for cough
Raw	Use toward the higher range for edema

Precautions:

• Cold-type cough (风寒咳嗽): Sang Bai Pi’s cold nature can worsen cough caused by Wind-Cold patterns. Avoid or combine with warming herbs.
• Spleen deficiency with loose stools (脾虚便溏): The cold, descending nature may aggravate digestive weakness. Use cautiously or combine with Spleen-strengthening herbs.

Modern Research

Contemporary pharmacological studies have provided evidence supporting several of Sang Bai Pi’s traditional applications:

• Hypotensive effect: Sang Bai Pi extract has demonstrated blood pressure-lowering properties in animal studies, validating its modern use for hypertension.
• Diuretic action: Studies confirm a mild diuretic effect, supporting its traditional use for edema.
• Expectorant effect: The herb promotes the secretion of respiratory tract mucus, facilitating expectoration — consistent with its use for productive cough.
• Anti-inflammatory properties: In vitro and animal studies show anti-inflammatory activity, which may underlie its effectiveness in heat-related respiratory conditions.

While these findings are promising, further clinical trials are needed to establish optimal dosing and confirm efficacy in human populations.

Key Takeaways

• Sang Bai Pi is the primary herb for draining Lung heat, relieving cough and wheezing by restoring the Lung’s descending function.
• It uniquely addresses both respiratory and fluid disorders through the Lung’s dual role in governing Qi and regulating water passages.
• Xie Bai San is its signature formula, pairing it with Di Gu Pi for comprehensive Lung heat clearance.
• Preparation matters: honey-fried for cough, raw for edema.
• The mulberry tree is a TCM treasure, with leaf, bark, twig, and fruit each serving distinct therapeutic roles.
• Use with caution in cold-type cough and Spleen deficiency patterns.

Disclaimer

This article is for educational purposes only and does not constitute medical advice. Traditional Chinese Medicine should be practiced under the guidance of a qualified practitioner. Do not self-prescribe herbs without professional consultation.

Related Articles

• Huang Qin (Scutellaria) — Another key heat-clearing herb often paired with Sang Bai Pi for Lung heat patterns
• Chen Pi (Tangerine Peel) — Sang Bai Pi’s companion in Wu Pi San for edema
• Zang-Fu Organ Theory — Understanding the Lung’s dual role in Qi and water regulation