Hirudo — Whitmania pigra Whitman, Hirudo nipponica Whitman (the dried whole body; an annelid worm)
Nature and flavour. Salty and bitter, neutral; listed as slightly toxic in the classical materia medica; Liver system.
The strongest of the stasis-breaking drugs, and the one where the classical account and modern medicine actually meet. Classical sources describe the dried leech as breaking blood and chasing out stasis, and record it for amenorrhoea, for abdominal masses attributed to blood stasis, for stabbing fixed pain, and for the bruising and swelling of traumatic injury. Separately from that tradition, the living leech is a real instrument in modern surgery: leech saliva contains hirudin, a direct thrombin inhibitor, and medicinal leeches are used in reconstructive and replantation surgery to relieve venous congestion in tissue whose venous drainage is not yet working. That clinical use is a supervised hospital procedure with a defined protocol — it is not the same activity as taking the dried drug, and it does not validate the traditional internal uses. For those traditional internal uses, the modern clinical evidence is limited and is not established.
性味归经。咸、苦，平；传统本草列为有小毒；归肝经。
破血逐瘀药中最峻烈的一味，也是古典记载与现代医学真正碰面的一味。古籍记载干品水蛭破血、逐瘀，用于经闭、瘀血所致的癥瘕、固定刺痛，以及跌打损伤的瘀肿。与这条传统并行的另一件事实是：活体水蛭是现代外科中真实使用的器械 —— 水蛭唾液含蛭素（直接凝血酶抑制剂），在重建与再植手术中用于缓解静脉回流尚未建立时的组织淤血。那是医院内有规范、有人监督的操作，与服用干品不是同一件事，也不能反过来证明传统内服用途成立。就上述传统内服用途而言，现代临床证据有限，尚未被证实。
传统列为有小毒，且其出血风险是实在的、而非理论上的。孕期禁用 —— 古典理由是其破血。有出血倾向者、活动性溃疡患者、血小板极低者、术前患者不宜；与华法林及其它抗凝药、抗血小板药同用的相互作用顾虑已有文献记载，且不是小事，因为该动物本身就是抗凝物质的来源。活体医用水蛭肠道内正常共生气单胞菌，这正是医院水蛭疗法需预防性使用抗生素的原因：叮咬处感染是已知并发症。水蛭叮咬后长时间出血导致贫血亦有记载。医用水蛭必须来自持证医疗供应商，绝不可取自池塘、钓具店或市场。本品任何形态都不属于可自行使用之物，须在合格执业者监督下使用；本页刻意不回答「该用多少」这个问题。
1 related entry.