Therapeutic Effects and Functions of Hirudo (Leech)

Leeches are a commonly used traditional Chinese medicinal herb. Their therapeutic effects and actions typically include breaking up stagnant blood and resolving blood stasis, promoting blood circulation and regulating menstruation, unblocking the meridians and activating collaterals, providing local anesthesia and analgesia, and exerting anticoagulant effects. A detailed analysis follows:

1. Breaking Up Stagnant Blood and Resolving Blood Stasis

Leeches have a bitter and salty taste and a neutral nature, entering the Liver channel. They possess the effect of breaking up stagnant blood and resolving blood stasis. Hirudin—the active component in leeches—inhibits platelet activity, thereby exerting anticoagulant effects and alleviating symptoms such as traumatic injuries, contusions, swelling, and pain due to blood stasis.

2. Promoting Blood Circulation and Regulating Menstruation

By inhibiting coagulation and enhancing blood circulation, leeches effectively treat menstrual disorders caused by blood stasis—such as amenorrhea, dysmenorrhea, reduced menstrual flow, and prolonged menstrual cycles. They are frequently employed to relieve discomfort associated with conditions like blood-stasis-induced amenorrhea and abdominal masses (e.g., fibroids or tumors).

3. Unblocking the Meridians and Activating Collaterals

Leeches help unblock the meridians and activate collaterals, thus improving symptoms such as hemiplegia following stroke and pain in the chest or abdomen due to blood stasis. They are often combined with other herbs—including earthworm (Pheretima), Angelica sinensis (Danggui), and Carthamus tinctorius (Honghua)—to promote blood circulation, resolve blood stasis, unblock meridians, and activate collaterals, thereby serving as an adjunctive therapy.

4. Local Anesthesia and Analgesia

Hirudin present in leeches exhibits local anesthetic properties. When applied to wounds accompanied by significant localized pain, leeches can provide effective anesthesia and pain relief.

5. Anticoagulation

Leech saliva contains multiple biologically active enzymes that inhibit the blood coagulation cascade and prevent thrombus formation, thereby producing anticoagulant effects. Extracts from leeches and purified hirudin significantly suppress platelet aggregation, helping alleviate symptoms associated with thrombotic disorders—including cerebral thrombosis and coronary artery atherosclerotic heart disease.

Leeches possess mild toxicity; therefore, their use must be supervised by a qualified healthcare professional. Self-administration without medical guidance is strongly discouraged. Pregnant women must avoid leeches entirely, as their blood-activating and stasis-resolving effects may trigger miscarriage. During treatment with leeches, patients should maintain a light diet and avoid greasy, spicy, or otherwise irritating foods, which could interfere with drug absorption and therapeutic efficacy.