Leech (Shuizhi): A Highly Contested Chinese Herb in Oncology

The leech (mahuang) is a Chinese herb commonly used in oncology. Whether leech should be used in tumor patients is controversial in academic circles. Some scholars believe hirudin carries the risk of promoting hematogenous metastasis of cancer cells, while others believe leech helps improve tumor patients' symptoms and that its side effect of promoting hematogenous metastasis can be offset by combining it with other herbs. Both views are influential, and the controversy is fierce.

Consulting the Zhonghua Bencao (Chinese Materia Medica) and the Zhongyao Da Cidian (Dictionary of Chinese Materia Medica), the two most authoritative modern Chinese-medicine reference works, there are few records of leech's anticancer effect; only the Zhongyao Da Cidian mentions that oral gavage of leech extract can induce apoptosis in leukemia L1210 tumor cells in tumor-bearing mice.

Animal experiments have mainly confirmed the anticoagulant effect of leech. Hirudin, isolated from the head of the leech, is the most potent specific thrombin inhibitor known to date; it inhibits thrombin, stimulates fibroblast proliferation, and contracts smooth muscle cells. In Chinese-medicine terms, leech has a very strong effect of activating blood and resolving stasis. So leech is mainly used as an anticoagulant and thrombolytic drug. Medicinal leech has a long history of use in Europe, and related anticoagulants made from hirudin have been approved by the US FDA.

Traditional Chinese medicine holds that leech is salty and bitter in flavor, neutral in nature, and toxic, entering the liver meridian. Some materia medica works also hold that leech enters the liver and bladder meridians (such as Bencao Zaixin and Yaoyao Fenji), probably because their authors believed leech promotes urination. In fact, leech improves urinary retention in patients with enlarged prostate because of its blood-activating and stasis-resolving effect.

Chinese medicine summarizes leech's effects as breaking blood and expelling stasis, unblocking menstruation and dissipating zheng-jia masses, and it mainly treats blood-stasis amenorrhea, zheng-jia abdominal masses, and traumatic injuries. This summary is quite accurate; the Chinese-medicine concept of zheng-jia masses includes both stasis-induced swellings and various benign and malignant tumors. Because of its strong anticoagulant effect, leech may inhibit tumor angiogenesis, disrupting or even destroying the vascular tissue within tumors, thereby shrinking or even eliminating tumors. But at the same time, it does indeed increase the risk of hematogenous metastasis of the tumor.

Searching the literature, I have indeed not seen many records of leech's anticancer effect in authoritative sources. But I have come into contact with several Chinese-medicine physicians who commonly use leech, and their anticancer results are commendable, such as the late renowned Beijing physician Professor Kong Sibo and the present Professor Pei Yongqing of Beijing University of Chinese Medicine.

I have personally seen prescriptions they wrote for patients in which leech was used heavily—both elders incorporated the leech-containing Didang Tang as a component of their formulas, and they often combined this formula with Shengjiang San, Shengmai Yin, Sanren Tang, and Wuwei Xiaodu Yin.

I have met the cancer patients they treated successfully, and I personally collected the prescriptions from these patients or their families. I did not see in these patients the side effect of cancer metastasis that scholars who claim leech promotes hematogenous metastasis warn of; on the contrary, I saw their tumors regress and their survival times be extraordinarily long.

So I believe that, under the principle of pattern differentiation and treatment, whether using leech in cancer patients is beneficial or harmful requires further research. Aspirin is also an anticoagulant; in theory this kind of anticoagulant could also promote hematogenous metastasis of cancer cells, but some large European studies (with samples exceeding 100,000 people) show that long-term aspirin use can extend cancer patients' survival by more than 30%.

New findings from modern pharmacological research have broadened the range of leech's application. In modern times, leech preparations are used not only for traditional conditions such as blood-stasis amenorrhea but also widely in treating hyperlipidemia, cerebral hemorrhage, myocardial infarction, coronary heart disease, cor pulmonale, enlarged prostate, and many other diseases—precisely employing leech's blood-activating and stasis-resolving effect. Leech can unblock vessels and improve the symptoms caused by cardiovascular and cerebrovascular blockage, and can also treat common conditions such as enlarged prostate and uterine fibroids.

Traditional Chinese medicine mostly uses processed leech; but processing destroys hirudin, the active component. So Zhang Xichun pointed out: "Leech is best used raw; fire-roasting is strictly forbidden." Zhang Xichun also gave an example of a gynecological patient to prove this. The patient had previously seen a physician who used leech, but that physician fire-roasted the leech in sesame oil before using it, with no effect. Later Zhang Xichun treated the same patient with leech, only switching to raw leech, and obtained an immediate effect.

But raw leech tastes extremely foul and fishy; I once ground raw leech, and the stench made me retch. So when using raw leech to treat disease, it should either go into decoction or be put into capsules or pills; one should avoid having patients take it as a powder.