Lignum Sappan — Caesalpinia sappan L. (accepted name Biancaea sappan (L.) Tod.), the dried heartwood
Nature and flavour. Sweet and salty, neutral. Heart, Liver and Spleen systems.
A red heartwood, and a reminder that a great deal of the materia medica did double duty as trade goods: sappan wood was a major export of Southeast Asia for centuries, used as a red dye for textiles and as a colourant, and the same wood entered medicine. Its red principle is brazilin, which oxidises to the red brazilein; a close relative, logwood (Haematoxylum campechianum), yields haematoxylin, which is still used as a histological stain — a useful illustration that a dye and a drug are not separate categories in this material. Classical sources describe it as quickening the blood and opening the menses, dispersing stasis and settling pain, and record it for amenorrhoea and painful periods held to be stasis, for postpartum stasis and abdominal pain, for stabbing pain in the chest and abdomen, and for the swelling and pain of traumatic injury. It is a blood mover of moderate strength rather than a breaker, and the classical texts put it a clear step below 三棱 and 莪术. Modern clinical evidence for these uses is limited and is not established.
性味归经。甘、咸，平。归心、肝、脾经。
一味红色心材，也提醒人本草里有相当一部分同时是商品：苏木数百年来是东南亚的重要出口品，既作纺织红色染料与着色料，也入药。其红色成分是巴西苏木素，氧化后成为红色的巴西苏木红素；近缘的洋苏木（Haematoxylum campechianum）所含的苏木精至今仍用作组织学染色剂 —— 这一点很好地说明：在这批材料里，染料与药物并不是两个分开的类别。古籍记载其活血通经、散瘀止痛，用于经闭痛经（属瘀血者）、产后瘀阻腹痛、胸腹刺痛，以及跌打损伤的肿痛。它的活血之力属中等而非破削，古籍明确把它放在三棱、莪术之下一个台阶。上述用途的现代临床证据有限，尚未被证实。
属活血药，故孕期禁用，古籍对无瘀者亦有禁忌。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同用的相互作用顾虑已有文献记载。此类木材是已知的接触性皮炎成因，其粉尘也会引起呼吸道刺激，接触后出现皮疹或气喘应当停用并就诊，而不是继续。由于它长期作为染料使用，苏木也以着色料与手工材料的身份流通，从这些渠道买到的材料在品种与洁净度上没有任何保证。不同市场还有其它红色木材以相似名称流通。不属于可自行使用的药材，须在合格执业者监督下使用。