Rehmanniae Radix
Dihuang (Rehmannia Root), a Chinese medicinal, is the fresh or dried tuberous root of Rehmannia glutinosa Libosch., a plant of the Scrophulariaceae family. It is mainly produced in Henan Province. It is dug in autumn, the rhizome crown, fibrous roots and sediment are removed, and then it is used fresh; or the root is slowly baked until about 80% dry. The former is commonly known as “Xian Dihuang” (fresh Rehmannia root), and the latter as “Sheng Dihuang” (raw Rehmannia root).
Efficacy & Actions
Fresh Rehmannia (Xian Dihuang): Clear heat and promote fluid production; cool the blood and stop bleeding. Raw Rehmannia (Sheng Dihuang): Clear heat and cool the blood; nourish yin and promote fluid production. Prepared Rehmannia (Shu Dihuang): Tonify blood and nourish yin; supplement essence and fill the marrow.
Indications
Fresh Rehmannia (Xian Dihuang): Indicated for fluid damage in febrile diseases, deep‑red tongue with vexation and thirst, skin eruptions and macules, hematemesis and epistaxis, sore throat. Raw Rehmannia (Sheng Dihuang): Indicated for heat entering the nutritive and blood levels, warm-toxin causing macules, hematemesis and epistaxis, fluid damage in febrile diseases, deep‑red tongue with vexation and thirst, constipation due to fluid damage, yin deficiency fever, bone‑steaming consumptive fever, internal heat with wasting thirst disorder. Prepared Rehmannia (Shu Dihuang): Indicated for sallow complexion due to blood deficiency, palpitations and severe palpitations (zhengchong), irregular menstruation, flooding and spotting (metrorrhagia), liver‑kidney yin deficiency, soreness and weakness of the lower back and knees, bone‑steaming tidal fever, night sweats and spermatorrhea, internal heat with wasting thirst disorder, dizziness and tinnitus, premature graying of beard and hair.
Modern Pharmacology
Hypoglycemic: Catalpol from Rehmannia lowers blood glucose and improves insulin resistance; used as an adjunctive treatment for diabetes. Immunomodulatory (enhances immunity): Rehmannia polysaccharides enhance the phagocytic function of macrophages and improve immune function. Anti‑aging and antioxidant: Scavenges free radicals and delays aging. Cardiovascular protection: Strengthens cardiac contraction, lowers blood pressure, protects against myocardial ischemia, and prevents atherosclerosis. Hepatoprotective: Reduces chemical‑induced liver injury and promotes hepatocyte regeneration. Hemostatic: Raw and fresh Rehmannia shorten clotting time; used for bleeding due to blood heat. Blood‑tonifying: Prepared Rehmannia (Shu Dihuang) promotes hematopoietic function, increases red blood cells and hemoglobin. Anti‑inflammatory: Inhibits the release of inflammatory mediators. Antitumor: Inhibits certain tumor cells.
Ingredients
Iridoid glycosides: Catalpol, rehmannioside A, B, C, D, leonuride, aucubin, etc. Catalpol is one of the main active components of Rehmannia root. Sugars (carbohydrates): Stachyose, raffinose, sucrose, glucose, etc. Rehmannia root has a high sugar content, especially stachyose. Amino acids: Arginine, glutamic acid, aspartic acid, and more than ten other amino acids. Others: Organic acids (e.g., ferulic acid), vitamin A‑like substances, trace elements (iron, zinc, copper, manganese, etc.).
Usage & Dosage
Fresh Rehmannia (Xian Dihuang): 12–30 g in decoction; or crushed for fresh juice. Raw Rehmannia (Sheng Dihuang): 10–15 g in decoction; large doses may be used up to 30 g. Prepared Rehmannia (Shu Dihuang): 9–15 g in decoction; or used in pills, powders, extracts, or wine preparations.
Contraindications
Fresh/Raw Rehmannia contraindications: Avoid in cases of spleen‑stomach deficiency cold, loose stools, qi stagnation with profuse phlegm. Prepared Rehmannia contraindications: Avoid in cases of spleen‑stomach deficiency, qi stagnation with profuse phlegm, abdominal distension and loose stools. Should not be taken together with radish, scallion white, or Chinese onion (Allium macrostemon). General precautions for all Rehmannia preparations: Should not be used together with Veratrum nigrum (Lilu) – according to the “Eighteen Incompatibilities”. Use with caution during pregnancy.
Selected Formulas
Raw Rehmannia (Shengdihuang) with Xuan shen (Scrophularia root) and Maidong (Ophiopogon root): Clears heat, nourishes yin, and promotes fluid production. Indicated for fluid consumption with dry mouth and tongue after febrile disease – as in Zengye Tang (Fluid‑Increasing Decoction). Raw Rehmannia with Shui nujiao (water buffalo horn) and Mudanpi (Moutan bark): Clears heat, cools blood, and resolves toxicity. Indicated for heat entering the nutrient‑blood level with skin rashes – as in Xijiao Dihuang Tang (Rhinoceros Horn and Rehmannia Decoction; now water buffalo horn is used as a substitute). Prepared Rehmannia (Shudihuang) with Danggui (Angelica root) and Chuanxiong (Szechwan lovage): Enriches and nourishes blood. Indicated for blood deficiency pattern – as in Siwu Tang (Four‑Substance Decoction). Prepared Rehmannia with Shanyao (Chinese yam) and Shanzhuyu (Cornus fruit): Nourishes kidney yin. Indicated for kidney yin deficiency pattern – as in Liuwei Dihuang Wan (Six‑Ingredient Rehmannia Pill). Prepared Rehmannia with Zhimu (Anemarrhena) and Huangbai (Phellodendron): Nourishes yin and reduces fire. Indicated for yin deficiency with fire hyperactivity and bone‑steaming tidal fever – as in Zhibai Dihuang Wan (Anemarrhena, Phellodendron and Rehmannia Pill).
Daily Consumption
1. Sheng Dihuang Congee (Raw Rehmannia Congee) Ingredients: 15 g raw rehmannia (Sheng Dihuang), 50 g japonica rice. Preparation: Cook together to make congee. Indication: For fluid damage in febrile diseases, dry mouth and throat. 2. Shu Dihuang Chicken Soup (Prepared Rehmannia Chicken Soup) Ingredients: 15 g prepared rehmannia (Shu Dihuang), 1 hen, 5 red dates (jujube). Preparation: Stew all ingredients together for 2 hours. Indication: For sallow complexion due to blood deficiency, soreness and weakness of the lower back and knees. 3. Shu Dihuang and Yam Congee (Prepared Rehmannia and Chinese Yam Congee) Ingredients: 10 g prepared rehmannia (Shu Dihuang), 30 g Chinese yam (Shanyao), 50 g japonica rice. Preparation: Cook together to make congee. Indication: For kidney yin deficiency with soreness and weakness of the lower back and knees.
Medicinal Parts
tuberous root
Selection & Storage
Fresh Rehmannia (Xian Dihuang): Store in a cool, damp place, protected from freezing. Alternatively, bury in sand for preservation. Raw Rehmannia (Sheng Dihuang) and Prepared Rehmannia (Shu Dihuang): Store in a well-ventilated, dry place, protected from mold and insects. Prepared Rehmannia has a high sugar content and is prone to moisture absorption; it should be kept in an airtight container.