Ingredient Animal — whole (全虫 quán chóng)

Shui Zhi

Leech · 水蛭

Whitmania pigra Whitman, Hirudo nipponica Whitman, Whitmania acranulata Whitman · Hirudo

Also known as: Ma Huang (蚂蟥)

Shui Zhi (Leech) plant

Images shown are for educational purposes only

Shuǐ Zhì (leech) is one of the most powerful Blood stasis-breaking substances in Chinese medicine, used when stubborn, long-standing Blood stagnation resists milder herbs. It is primarily used for conditions involving fixed abdominal masses, absent menstruation due to Blood clots, traumatic injuries with internal bruising, and the aftermath of stroke. Despite its strong action, classical texts note it breaks up old stagnant Blood without harming healthy new Blood.

Category Blood-invigorating and stasis-dispelling herbs (活血化瘀药) Blood-breaking and mass-dispersing herbs (破血消癥药)
Therapeutic focus Cardiovascular Health Menstrual Health Stroke Recovery Injury and Trauma Recovery

TCM Properties

Temperature

Neutral

Taste

Salty (咸 xián), Bitter (苦 kǔ)

Channels entered

Liver, Urinary Bladder

Parts used

Animal — whole (全虫 quán chóng)

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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 Shui Zhi does in the body, explained in both everyday and TCM terms

Therapeutic focus

In practical terms, Shui Zhi is primarily used to support these areas of health:

Cardiovascular Health Menstrual Health Stroke Recovery Injury and Trauma Recovery

TCM Actions

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

Breaks Blood and Dispels Stasis Promotes Menstruation Disperses Accumulations and Dissipates Nodules

How these actions work

'Breaks Blood and expels stasis' means Shuǐ Zhì powerfully disperses old, stubborn Blood stagnation that has been stuck in the body for a long time. Unlike milder Blood-moving herbs such as Peach Kernel or Safflower, Shuǐ Zhì targets deeply lodged, hardened clots of stagnant Blood that resist gentler treatment. Its salty taste allows it to penetrate into the Blood level, while its bitter taste helps it push downward and break through blockages. Classically, this is expressed as 'salty enters the Blood, bitter purges stagnation' (咸入血走血，苦泄结). A key classical observation is that Shuǐ Zhì breaks up old stagnant Blood without damaging fresh, healthy Blood. This makes it especially valuable for long-standing Blood stasis conditions.

'Unblocks the channels and promotes menstruation' means it restores menstrual flow that has been blocked by Blood stasis. When stagnant Blood obstructs the uterine vessels and the Chōng and Rèn meridians, menstruation stops. Shuǐ Zhì's powerful stasis-breaking action clears these obstructions so that normal menstrual flow can resume. This is one of its most ancient recorded uses, dating back to the Shén Nóng Běn Cǎo Jīng.

'Disperses masses and accumulations' refers to its ability to break down fixed abdominal masses (癥瘕 zhēng jiǎ) caused by chronic Blood stasis. In TCM, when stagnant Blood accumulates over time, it can solidify into palpable lumps in the abdomen. Shuǐ Zhì, as an animal-derived substance with a natural affinity for blood, gradually penetrates and dissolves these hardened masses. It enters the Liver channel, which governs Blood storage and the smooth flow of Qi, making it particularly effective at addressing stasis in the Blood level of the Liver system.

Patterns Addressed

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

Why Shui Zhi addresses this pattern

Shuǐ Zhì directly targets the core pathomechanism of Blood Stasis. Its salty taste penetrates the Blood level and its bitter taste drives downward to break through obstructions. Entering the Liver channel (which governs Blood storage and smooth flow), it powerfully breaks up stagnant Blood that has become fixed and hardened. As a blood-feeding animal, it has what classical texts call a natural 'affinity' for stagnant Blood, seeking it out and dissolving it gradually without injuring fresh Blood. This makes it especially suited for severe or chronic Blood Stasis where lighter herbs like Peach Kernel or Safflower have been insufficient.

A practitioner would look for one or more of these signs

Amenorrhea

Menstrual absence due to Blood stasis obstruction

Abdominal Pain

Fixed, stabbing lower abdominal pain that worsens with pressure

Dark Menstrual Clots

Dark clotted menstrual blood when flow does occur

Pale Tongue

Purple or dark tongue with stasis spots

Commonly Used For

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

Arises from: Blood Stasis in the Chest

TCM Interpretation

TCM understands stroke (中风 zhòng fēng) as a condition where internal imbalances lead to obstruction of the brain's vessels and channels. The most common underlying pattern involves a combination of Qi deficiency and Blood stasis. When Qi is too weak to push Blood through the vessels, Blood slows down and clots. Over time, these clots block the channels that supply the brain, causing sudden paralysis, speech problems, or loss of consciousness. The Liver plays a central role because it governs the smooth flow of Qi and stores Blood. When Liver function is disrupted (often by rising Liver Yang or Liver Wind), it further contributes to the chaotic movement of Blood and formation of stasis.

Why Shui Zhi Helps

Shuǐ Zhì is one of the most important herbs for post-stroke recovery because it powerfully breaks up the Blood stasis that is blocking circulation to the brain. Unlike plant-based Blood movers, Shuǐ Zhì is an animal substance with what classical texts describe as a 'penetrating, seeking' quality that can reach into deep, stubborn clots. Its neutral temperature makes it safe to use whether the underlying stroke pattern involves Heat or not. Zhang Xichun, the famous late-Qing dynasty physician, specifically praised Shuǐ Zhì for its ability to break up stagnant Blood without harming new Blood or damaging Qi. Modern clinical practice often combines Shuǐ Zhì with Huáng Qí (Astragalus) to simultaneously address the Qi deficiency and Blood stasis that characterise most stroke presentations.

Also commonly used for

Deep Vein Thrombosis

Blood clots in veins

Angina

Chest pain from coronary artery disease

Trauma

Internal bruising from falls, blows, or fractures

Hyperlipidemia

High blood lipids with blood viscosity

Endometriosis

Pelvic Blood stasis with pain

Cirrhosis

With Blood stasis and abdominal masses

Ingredient Properties

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

Temperature

Neutral

Taste

Salty (咸 xián), Bitter (苦 kǔ)

Channels Entered

Liver Urinary Bladder

Parts Used

Animal — whole (全虫 quán chóng)

Dosage & Preparation

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

Standard dosage

1–3g (powder/capsule); 3–6g (decoction)

Maximum dosage

Up to 6g in decoction or 3g as powder for severe Blood stasis conditions. Reported toxic dose is 15–30g; do not exceed standard doses without expert supervision.

Dosage notes

Shui Zhi is most commonly used as a ground powder in capsules or pills (1–3g per day) rather than in decoctions, because the key bioactive compound hirudin is a protein that is partially destroyed by prolonged boiling. Research suggests that unprocessed ground powder has higher fibrinolytic and anticoagulant activity than the talcum-fried processed form, though the latter is more traditional and easier to take due to reduced fishy smell. For decoctions: 3–6g, typically combined with other Blood-moving herbs (Tao Ren, Da Huang) as in Di Dang Tang. For powder/capsules: 1–1.5g per dose, 2–3 times daily, is the standard range. Lower doses (1–2g powder) are used for chronic cardiovascular conditions like coronary artery disease or post-stroke rehabilitation. Higher doses (up to 3g powder or 6g decoction) are reserved for acute Blood stasis conditions with clearly palpable masses, severe amenorrhea, or acute traumatic injury. Zhang Xichun in Yi Xue Zhong Zhong Can Xi Lu advocated using raw (unprocessed) Shui Zhi powder at approximately 1.5g doses for stubborn masses, finding it more effective than the fried form.

Preparation

If using in decoction, Shui Zhi can be decocted normally with the other herbs. However, because hirudin and other bioactive proteins are heat-sensitive, prolonged boiling reduces efficacy. For this reason, modern clinical practice often favors taking Shui Zhi as ground powder in capsules (swallowed directly, not decocted) to preserve maximum therapeutic activity. When using as a decoction ingredient, do not over-boil. The processed (talcum-fried) form is traditional for decoctions and pills, as it reduces the strong fishy smell and makes the material easier to grind.

Processing Methods

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

Processing method

Clean Shuǐ Zhì segments are stir-fried with talcum powder (滑石粉) using the 'scalding method' (烫法) until they slightly puff up and become crisp.

How it changes properties

The thermal nature remains neutral. Scalding with talcum powder reduces the fishy smell, makes the material easier to grind into powder, and is believed to reduce the slight toxicity. The Blood-breaking action is somewhat moderated compared to the raw form, making it safer for oral use in decoctions and pills.

When to use this form

This is the standard processed form used in most clinical prescriptions today, as specified in the Chinese Pharmacopoeia. It is preferred for internal use in decoctions, pills, and powders because it is safer and easier to handle than the raw form.

Common Ingredient Pairs

These ingredients are traditionally combined with Shui Zhi for enhanced therapeutic effect

Meng Chong
Meng Chong 1:1 (historically 30 pieces each in Dǐ Dāng Tāng)

Shuǐ Zhì and Méng Chóng (gadfly) are the classical Blood-breaking pair, used together since the Shāng Hán Lùn. Shuǐ Zhì acts slowly and persistently, penetrating deeply to dissolve stubborn stasis, while Méng Chóng acts swiftly and fiercely to break open acute obstructions. Together they create a complementary action where one provides sustained power and the other provides immediate breakthrough force, making the pair far more effective than either alone at clearing severe Blood stasis.

When to use: Severe Blood stasis in the lower abdomen with absent menstruation, mania or delirium from stagnant Blood, or hardened lower abdominal masses with dark stool. This is the core pair in Dǐ Dāng Tāng.

Tao Ren
Tao Ren Shuǐ Zhì 3g : Táo Rén 9-12g

Shuǐ Zhì breaks Blood stasis from the animal/insect level with its penetrating, seeking quality, while Táo Rén (peach kernel) invigorates Blood and moistens the intestines from the plant level. Shuǐ Zhì handles the deep, stubborn clots while Táo Rén smooths general Blood circulation and helps expel stagnant material through the bowels. The combination covers both the deep breaking and the gentle moving aspects of Blood stasis treatment.

When to use: Blood stasis amenorrhea, post-traumatic internal bleeding, or abdominal masses. Appears together in Dǐ Dāng Tāng and Dà Huáng Zhè Chóng Wán.

Huang Qi
Huang Qi Huáng Qí 30-60g : Shuǐ Zhì 3-6g (large ratio reflecting the need to strongly support Qi while cautiously breaking stasis)

Huáng Qí tonifies Qi powerfully while Shuǐ Zhì breaks Blood stasis. This pairing addresses the common clinical reality that Qi deficiency and Blood stasis often coexist: weak Qi fails to push Blood, so Blood stagnates. Huáng Qí restores the driving force behind circulation while Shuǐ Zhì clears the accumulated clots. Together they treat both the root (Qi deficiency) and the branch (Blood stasis) simultaneously.

When to use: Post-stroke recovery with hemiplegia, cardiovascular disease with fatigue and Blood stasis, or chronic conditions where both weakness and stagnation are present.

Di Long
Di Long 1:2 to 1:3 (Shuǐ Zhì 3g : Dì Lóng 6-10g)

Both are animal substances with salty taste that enter the Blood level. Shuǐ Zhì excels at breaking up existing Blood clots, while Dì Lóng (earthworm) is better at unblocking the channels and improving circulation through constricted vessels. Together they provide comprehensive vascular support: Shuǐ Zhì removes the old clots while Dì Lóng keeps the channels open afterward.

When to use: Post-stroke hemiplegia, chronic cardiovascular disease, or any condition with Blood stasis obstructing the channels and vessels.

Key Formulas

These well-known formulas feature Shui Zhi in a prominent role

Di Dang Tang 抵当汤 King

Dǐ Dāng Tāng from the Shāng Hán Lùn is THE defining formula for Shuǐ Zhì, showcasing its most powerful application. Shuǐ Zhì serves as the King herb (alongside Méng Chóng) in this four-herb formula that treats severe Blood stasis in the lower abdomen with mania, hardness below the navel, dark stool, and absent menstruation. This formula demonstrates Shuǐ Zhì at its most characteristic: breaking through deeply entrenched, stubborn Blood stasis that no milder herb can touch.

Da Huang Zhe Chong Wan 大黄蛰虫丸 Deputy

This Jīn Guì Yào Lüè formula treats 'dry Blood' (干血) from chronic deficiency and stasis: emaciation, rough scaly skin, dark eye sockets, and deep exhaustion. Shuǐ Zhì serves as Deputy, contributing its stasis-breaking power alongside five other Blood-moving substances. The formula illustrates an important clinical principle: even in severely weakened patients, Shuǐ Zhì can be used safely because it breaks old stasis without harming new Blood, and the pill form provides gradual, sustained action rather than an aggressive purge.

Comparable Ingredients

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

San Leng
Shui Zhi vs San Leng

Both Shuǐ Zhì and Sān Léng break up Blood stasis and disperse masses. However, Sān Léng is a plant-based herb that is stronger at quickly attacking and breaking up accumulations but more easily injures normal Qi. Shuǐ Zhì, being an animal substance, penetrates more gradually and deeply into stubborn, chronic stasis, and classical authorities note it breaks stagnant Blood without harming healthy Blood or damaging Qi. Choose Shuǐ Zhì for deep-seated, chronic stasis (especially in cardiovascular or post-stroke conditions); choose Sān Léng for acute masses with Qi stagnation.

Tu Bie Chong
Shui Zhi vs Tu Bie Chong

Both are animal-derived Blood-breaking herbs that enter the Liver channel. Tǔ Biē Chóng (ground beetle) is cold in nature and better suited to Blood stasis with Heat, especially in cases of traumatic injury where it also helps reconnect broken sinews and bones. Shuǐ Zhì is neutral in temperature and more specialised for chronic internal Blood stasis, abdominal masses, and vascular obstruction. Tǔ Biē Chóng is the go-to insect for trauma; Shuǐ Zhì is the go-to for chronic stasis in the vessels and uterus.

E Zhu
Shui Zhi vs E Zhu

Both break Blood stasis and disperse masses. É Zhú (Curcuma rhizome) also strongly moves Qi and is better when Qi stagnation accompanies Blood stasis, particularly in digestive system masses. Shuǐ Zhì works more purely in the Blood level without significant Qi-moving action, making it preferable for vascular Blood stasis (stroke, thrombosis) where the primary problem is clotted Blood rather than stagnant Qi.

Therapeutic Substitutes

Legitimate clinical replacements when Shui Zhi is unavailable, restricted, or contraindicated

Tu Bie Chong

Tu Bie Chong
Tu Bie Chong 土鳖虫
Ground beetle

Covers: Covers Shuǐ Zhì's core action of breaking Blood stasis (破血逐瘀) and unblocking the channels for patterns of fixed masses (癥瘕), amenorrhea due to stasis, and accumulation of old congealed Blood. Like Shuǐ Zhì, it is a salty, liver-channel insect drug that acts powerfully within the Blood level. Chinese clinical literature (including Baidu Health medical reference and practitioner guides citing Zhū Liáng Chūn's insect-drug tradition) explicitly lists Tǔ Biē Chóng as the primary single-herb replacement for Shuǐ Zhì when Shuǐ Zhì is unavailable or too strongly dispersing for a particular patient.

Does not cover: Tǔ Biē Chóng is consistently described as milder in blood-breaking force than Shuǐ Zhì — it is the weakest of the three classical blood-breaking insect drugs (Shuǐ Zhì > Méng Chóng > Tǔ Biē Chóng). It will not adequately substitute in cases of very severe, deeply entrenched Blood stasis (e.g. dry-Blood consumption, 干血痨) where Shuǐ Zhì's penetrating, sustained action is specifically required. Tǔ Biē Chóng also has an additional action of knitting bones and sinews that Shuǐ Zhì lacks — this is clinically useful but means the two are not equivalent across all indications. Cold nature of Tǔ Biē Chóng (vs. neutral for Shuǐ Zhì) must be considered in patients with Cold patterns.

Use when: When Shuǐ Zhì is unavailable, too expensive, or when the degree of Blood stasis is moderate rather than severe. Also appropriate when the patient has concurrent bone or sinew injury alongside Blood stasis, where Tǔ Biē Chóng's bone-knitting action adds clinical benefit. Typical substitute dose: 3–10g in decoction, or 1–1.5g as powder swallowed in capsules.

Identity & Adulterants

Related species and common adulterations to be aware of when sourcing Shui Zhi

The three pharmacopoeia-listed species (Whitmania pigra, Hirudo nipponica, and Whitmania acranulata) are all legitimate but have different traditional standings. Hirudo nipponica (the small blood-sucking species) is considered most consistent with the classical description of the medicinal leech and is considered the highest quality. Common substitution issues include: - Terrestrial or mountain leeches (山蛭), which were specifically excluded by Tao Hongjing and later authorities as non-medicinal. - Non-blood-sucking freshwater species that lack the bioactive salivary compounds (particularly hirudin) responsible for the therapeutic effect. - Heavily adulterated products padded with soil, stones, or metal filings to increase weight, as dried leech is expensive. - Improperly processed or poorly stored specimens that have become damp, moldy, or rancid, losing both efficacy and safety. Authentication tip: genuine Shui Zhi, when soaked in water, rehydrates into a recognizable segmented worm shape with visible suckers at both ends.

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

Toxicity Classification

Classical Chinese pharmacopoeia toxicity rating for Shui Zhi

Slightly toxic

The 2020 Chinese Pharmacopoeia classifies Shui Zhi as having 'slight toxicity' (有小毒). Historical texts varied: the Shen Nong Ben Cao Jing did not mention toxicity, the Ming Yi Bie Lu stated 'toxic,' and the Ben Cao Gang Mu stated 'slightly toxic.' The primary bioactive and potentially toxic components are hirudin (a potent direct thrombin inhibitor), heparin-like substances, and anti-thrombotic proteins. Overdose (reported toxic dose: 15–30g) can cause nausea, vomiting, bleeding gums, nosebleeds, subcutaneous bruising, excessive menstrual bleeding, hematuria, and in severe cases gastrointestinal hemorrhage, severe abdominal pain, and intracranial bleeding. Proper processing (炮制) significantly reduces these risks. The standard method is to stir-fry with talcum powder (滑石粉烫) until the leech segments puff up slightly and turn yellowish-brown, which reduces the potency of heat-labile proteins like hirudin while making the material brittle and easier to grind for pills and powders. At standard clinical doses (1–3g as powder, 3–6g in decoction), Shui Zhi has extremely low clinical toxicity. Modern research confirms that properly processed Shui Zhi at therapeutic doses is safe, though long-term use requires monitoring for allergic reactions and bleeding tendency.

Contraindications

Situations where Shui Zhi should not be used or requires extra caution

Avoid

Pregnancy. Shui Zhi is a powerful Blood-breaking herb that can stimulate uterine contractions and cause miscarriage. It is classified as a pregnancy-prohibited (禁用) substance in Chinese medical texts.

Avoid

Active bleeding or hemorrhagic conditions (e.g. hemorrhagic stroke, active gastrointestinal bleeding, hemophilia). Shui Zhi's potent anticoagulant properties can worsen uncontrolled bleeding.

Avoid

Absence of Blood stasis. Classical texts state that Shui Zhi is prohibited for those without genuine Blood stasis (无瘀血者禁用). Using it in patients with Qi or Blood deficiency alone, without stasis, risks depleting already weakened Blood.

Avoid

Menorrhagia or heavy menstrual bleeding. The Blood-breaking action can significantly worsen excessive menstrual flow.

Caution

Patients with severe thrombocytopenia or other coagulopathy disorders, where further impairment of clotting could be dangerous.

Caution

Patients with constitutional Qi and Blood deficiency who are frail and debilitated. Use with extreme caution, and only if Blood stasis is clearly present alongside the deficiency. Combine with tonifying herbs.

Caution

Perioperative period. Discontinue well before elective surgery due to its anticoagulant effects, which may increase surgical bleeding risk.

Caution

Patients with peptic ulcer disease or history of gastrointestinal bleeding. The anticoagulant activity may increase gastrointestinal bleeding risk.

Special Populations

Important considerations for pregnancy, breastfeeding, and pediatric use

Pregnancy

Absolutely contraindicated in pregnancy. Shui Zhi is classified as a pregnancy-prohibited (禁用) herb in Chinese medicine, alongside other powerful Blood-breaking substances like San Leng, E Zhu, and Meng Chong. Its potent Blood-breaking and stasis-dispelling action can directly stimulate uterine activity and provoke miscarriage. The active compound hirudin is a powerful thrombin inhibitor that could theoretically cross the placenta and affect fetal coagulation. Research on recombinant hirudin confirms it is not recommended in pregnancy due to transplacental passage. There are no circumstances where Shui Zhi should be used during pregnancy unless specifically required for termination under professional medical supervision.

Breastfeeding

There is no established safety data for Shui Zhi during breastfeeding. Given that its bioactive compounds (hirudin, heparin-like substances) are proteins and polypeptides, some transfer into breast milk is possible. Its strong Blood-breaking action could theoretically affect the nursing infant's developing coagulation system. It is generally considered inadvisable during breastfeeding unless the clinical need is urgent and the mother is under close practitioner supervision. If used, the infant should be monitored for signs of unusual bruising or bleeding.

Children

Shui Zhi is generally not used in pediatric practice due to its potent Blood-breaking properties and slight toxicity. Children's Qi and Blood are considered immature and easily damaged by such strong-acting substances. If absolutely necessary for a confirmed Blood stasis condition in older children (typically over 10 years), the dosage should be reduced to roughly one-third to one-half of the adult dose, used only for short courses, and prescribed by an experienced practitioner. It should be avoided entirely in infants and young children.

Drug Interactions

If you are taking pharmaceutical medications, be aware of these potential interactions with Shui Zhi

Anticoagulant drugs (warfarin, heparin, enoxaparin, dabigatran, rivaroxaban, apixaban): Shui Zhi contains hirudin, a potent natural direct thrombin inhibitor, along with heparin-like substances. Concurrent use with pharmaceutical anticoagulants creates a significant risk of synergistic anticoagulation, leading to excessive bleeding. INR monitoring is essential if any combination is necessary, though concurrent use is generally inadvisable.

Antiplatelet drugs (aspirin, clopidogrel, dipyridamole, ticagrelor): Shui Zhi has demonstrated antiplatelet effects in animal studies, including inhibition of ADP-induced platelet aggregation. Combined use with antiplatelet medications may increase bleeding risk through additive or synergistic mechanisms.

Thrombolytic drugs (streptokinase, alteplase, tenecteplase): The combination of Shui Zhi's natural thrombin inhibition with pharmaceutical thrombolysis poses a high risk of hemorrhagic complications and should be avoided.

NSAIDs (ibuprofen, naproxen, diclofenac): NSAIDs impair platelet function and can cause gastrointestinal mucosal damage. Combined with Shui Zhi's anticoagulant effects, there is an increased risk of gastrointestinal bleeding.

Dietary Advice

Foods and dietary considerations when taking Shui Zhi

Avoid cold, raw foods and iced drinks while taking Shui Zhi, as these can impede Blood circulation and work against the herb's stasis-breaking action. Avoid excessive consumption of foods that strongly promote Blood movement (such as large quantities of alcohol or very spicy foods) during treatment, as this may compound the anticoagulant effect and increase bleeding risk. A balanced diet that gently supports Blood circulation, including moderate amounts of warming, nourishing foods, is appropriate.

Botanical Description

Physical characteristics and morphology of the Shui Zhi source animal

Shui Zhi (水蛭) is not a plant but an animal-derived medicinal substance. It comes from leeches of the family Hirudinidae. The species used in Chinese medicine include Whitmania pigra Whitman (蚂蟥, the broad-bodied leech), Hirudo nipponica Whitman (日本医蛭, Japanese medicinal leech), and Whitmania acranulata Whitman (柳叶蚂蟥, willow-leaf leech).

These are segmented, soft-bodied aquatic annelid worms with flattened bodies. The broad-bodied leech (W. pigra) is spindle-shaped and 4–10 cm long, with a dark brown or black back, a flat yellowish-brown underside, and a sucker at each end. The Japanese medicinal leech (H. nipponica) is smaller, 2–5 cm long, cylindrical and often found curled or twisted, entirely dark brown-black in color. These leeches inhabit shallow freshwater environments such as ponds, lakes, paddy fields, marshes, and slow-flowing streams, where they feed on the blood of fish, frogs, and mammals.

Leeches breed from late April through June, depositing cocoons that hatch after 16–25 days. They reach maturity by autumn if conditions are favorable. Today, due to declining wild populations, commercial cultivation in managed ponds is increasingly common across China.

Sourcing & Harvesting

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

Harvesting season

Summer and autumn. Leeches are collected from freshwater habitats (ponds, paddy fields, lakes), then killed in boiling water and dried in the sun or at low temperature.

Primary growing regions

Shui Zhi is distributed widely across China in freshwater environments. The main producing regions include Shandong (especially around Weishan Lake), Jiangsu (around Taihu Lake), Anhui (Huaiyuan area), and Hubei (around Honghu Lake). Historically, the area around Weishan Lake in Shandong and Baiyangdian in Hebei were among the largest production bases. Due to declining wild populations from habitat loss and pesticide use, large-scale aquaculture farms now supply much of the commercial demand, with major cultivation operations in Shandong, Jiangsu, Anhui, Hubei, and Zhejiang provinces.

Quality indicators

For the broad-bodied leech (蚂蟥, Whitmania pigra, the most commonly used species): good quality specimens are flat and spindle-shaped, 4–10 cm long, with a dark brown-black back showing 5 faint longitudinal stripes when soaked, and a flat yellowish-brown belly. The texture should be brittle and easy to snap, with a shiny, gelatinous cross-section. The smell should be faintly fishy but not putrid. For the Japanese medicinal leech (水蛭, Hirudo nipponica): good quality pieces are small (2–5 cm), cylindrical, dark brown-black throughout, often twisted and strung together. They should snap cleanly with an uneven, non-glossy fracture surface. Processed (talcum-fried) Shui Zhi should appear slightly puffed, yellowish-brown, crisp, and easy to powder. Avoid specimens that are damp, moldy, have excessive earthy smell, or show signs of insect damage. In Sichuan, a variety with distinct yellow-green striping called 'gold-edge leech' (金边蚂蟥) is considered especially high quality.

Classical Texts

Key passages from the classical Chinese medical texts that describe Shui Zhi and its therapeutic uses

Shen Nong Ben Cao Jing (《神农本草经》)

Original: 水蛭，味咸平，主逐恶血、瘀血、月闭，破血瘕积聚，无子，利水道。生池泽。

Translation: Shui Zhi, salty and neutral in flavor. It drives out foul blood and stagnant blood, opens blocked menstruation, breaks Blood masses and accumulations, treats infertility, and promotes the water passages. It grows in marshes and ponds.

Tang Ye Ben Cao (《汤液本草》)

Original: 水蛭苦走血，咸胜血，仲景抵当汤用虻虫、水蛭，咸苦以泄畜血，故经云有故无殒也。

Translation: Shui Zhi's bitter flavor moves Blood and its salty flavor overcomes Blood. Zhongjing's Di Dang Tang uses Meng Chong and Shui Zhi, employing salty and bitter flavors to drain retained Blood. Thus the classics say: 'when there is a condition to treat, there is no harm.'

Ben Cao Jing Bai Zhong Lu (《神农本草经百种录》)

Original: 水蛭最喜食人之血，而性又迟缓善入，迟缓则生血不伤，善入则坚积易破，借其力以攻积久之滞，自有利而无害也。

Translation: The leech loves to consume human blood, yet its nature is slow-acting and penetrating. Being slow, it does not harm fresh blood; being penetrating, it easily breaks apart stubborn accumulations. Borrowing its power to attack long-standing stasis is beneficial without harm.

Ben Cao Jing Shu (《本草经疏》)

Original: 水蛭味咸苦气平，有大毒，其用与虻虫相似…咸入血走血，苦泄结，咸苦并行，故治妇人恶血、瘀血、月闭、血瘕积聚。

Translation: Shui Zhi is salty and bitter with a neutral nature, and has strong toxicity. Its use is similar to Meng Chong... Salty flavor enters and moves Blood, bitter flavor drains accumulations. Working together, they treat foul blood, stagnant blood, amenorrhea, and Blood masses in women.

Historical Context

The history and evolution of Shui Zhi's use in Chinese medicine over the centuries

Shui Zhi is one of the oldest animal-derived medicines in Chinese medicine, first recorded in the Shen Nong Ben Cao Jing (circa 1st–2nd century CE) under the 'Lower Grade' category, indicating its potent, targeted therapeutic action. The character 蛭 (zhì) is explained in the Shuo Wen Jie Zi as meaning 'a louse-like creature,' reflecting its small parasitic nature. Li Shizhen noted in the Ben Cao Gang Mu that the dialectal mispronunciation of 蛭 as 'chī' gave rise to folk names like 'water fool' (水痴). Other traditional names include Mǎ Qí (马蜞), Mǎ Biē (马鳖), and Ròu Zuān Zi (肉钻子, 'flesh drill'), the last vividly describing the leech's ability to burrow into skin.

Zhang Zhongjing (circa 150–219 CE) was the most influential early proponent of Shui Zhi, using it as a key ingredient in his famous Di Dang Tang (抵当汤) for treating lower-abdomen Blood stasis with mania or delirium, and in Da Huang Zhè Chong Wan for consumptive Blood stasis conditions. Remarkably, he used it even for severely debilitated patients, demonstrating his confidence that it attacks stagnant blood without harming healthy blood. Modern scholar Pei Yongqing of Beijing University of Chinese Medicine has championed this view, arguing that later physicians' fear of Shui Zhi was unfounded and that Zhongjing never described it as harmful to the body's Qi and Blood.

Li Shizhen's Ben Cao Gang Mu famously retells the story of the King of Chu who accidentally swallowed a leech while eating, only to find his chronic abdominal mass cured, as an illustration of the herb's Blood-breaking power. In modern times, the discovery of hirudin from leech saliva (first isolated in 1884 by Haycraft in Wales, and purified in 1955 by Markwardt in Germany) validated the traditional anticoagulant understanding and led to the development of pharmaceutical thrombin inhibitors including bivalirudin and dabigatran.

Modern Research

4 published studies investigating the pharmacological effects or clinical outcomes of Shui Zhi

1

Pharmacological Activities and Mechanisms of Hirudin and Its Derivatives - A Review (2021)

Dong H, Ren JX, Wang JJ, et al. Pharmacological Activities and Mechanisms of Hirudin and Its Derivatives - A Review. Frontiers in Pharmacology, 2021, 12: 660757.

This comprehensive review summarized two decades of research on hirudin, the key bioactive compound in leech. The review confirmed hirudin is the strongest known natural thrombin inhibitor, with potent anti-thrombotic effects. Beyond anticoagulation, the review documented emerging evidence for wound repair, anti-fibrosis, anti-tumor activity, effects on diabetic complications, and anti-hyperuricemia properties of hirudin and its derivatives.

PubMed
2

From Ancient Leech to Direct Thrombin Inhibitors and Beyond: New from Old - Review (2022)

Ferroni L, Gardin C, De Pieri A, et al. From ancient leech to direct thrombin inhibitors and beyond: New from old. Biomedicine & Pharmacotherapy, 2022, 149: 112878.

This historical pharmacology review traced the journey from ancient leech use to modern anticoagulant drug design. It detailed how hirudin, isolated from leech salivary glands, inspired the development of parenteral thrombin inhibitors (bivalirudin, argatroban) and the oral direct thrombin inhibitor dabigatran, as well as factor Xa inhibitors. The review highlighted that leech salivary glands contain over 100 bioactive proteins with multiple therapeutic properties beyond anticoagulation.

3

Cloning, Characterization, and Heterologous Expression of a Candidate Hirudin Gene from Hirudo nipponia (2023)

Electricwala A, et al. Cloning, characterization, and heterologous expression of a candidate Hirudin gene from the salivary gland transcriptome of Hirudo nipponia. Scientific Reports, 2023, 13: 5326.

This was the first study to clone and express recombinant hirudin from Hirudo nipponica (the species used in Chinese medicine as Shui Zhi). The researchers identified a 489-bp hirudin gene from the salivary gland transcriptome, successfully produced recombinant hirudin in a yeast expression system, and confirmed it possessed the structural motifs needed to bind and inhibit thrombin. This provides a molecular basis for the traditional use of this specific leech species.

4

Medicinal Leech Therapy - An Overall Perspective (Review, 2017)

Sig AK, Guney M, Uskudar Guclu A, et al. Medicinal leech therapy - an overall perspective. Integrative Medicine Research, 2017, 6(4): 337-343.

This integrative review evaluated the overall evidence for medicinal leech therapy across both traditional and modern medical contexts. It found growing evidence supporting leech therapy in plastic and reconstructive microsurgery (particularly for venous congestion relief in flap surgery), osteoarthritis pain management, and various inflammatory conditions. The review also addressed safety, noting that adverse effects are generally mild when leeches are properly handled.

Research on individual TCM herbs is growing but still limited by Western clinical trial standards. These studies provide emerging evidence and should be considered alongside practitioner expertise.