Isatis: A Comprehensive Encyclopedic Reference
1. Identity: Botanical and Chemical Overview
Species and Taxonomy
Isatis tinctoria L. (Brassicaceae), commonly known as woad, is a species with an ancient and well-documented history as an indigo dye and medicinal plant. Isatis indigotica Fort. (Chinese woad) is a closely related species with an equally well-documented history as an indigo dye and medicinal plant, but it is often confused with Isatis tinctoria L. (European woad). The two species are distinct in their primary geographic and pharmacological contexts, but they share many chemical constituents and are frequently used interchangeably in the literature. Isatis indigotica Fortune is a biennial of the Cruciferae (Brassicaceae) family, primarily cultivated in China, where it was a staple in indigo dye manufacture until the end of the 17th century; today it is used primarily as a therapeutic herb in traditional Chinese medicine (TCM).
The genus Isatis L., which belongs to the Brassicaceae family, comprises about 80 herbaceous annual to perennial species diffused in the Middle East and central Asia and beyond. Isatis indigotica Fort. is mainly distributed in the Gansu, Shaanxi, Hebei, Shandong, Jiangsu, Zhejiang, Anhui, and Guizhou provinces of China.
Morphology
Isatis tinctoria is a biennial herb reaching 60–90 cm tall, with grey-green lanceolate leaves and clusters of small yellow flowers in its second year; the root is long and fusiform and is sometimes used in formulations. The plant is a herbaceous biennial that typically forms a rosette of silvery-green leaves during its first year, then bolts in the second year to produce slender, erect stems topped with yellowish-white flowers.
Names, Parts Used, and Common Preparations
The medicinal use of I. indigotica is separated into its leaves (Da-Qing-Ye, Folium Isatidis) and roots (Ban-Lan-Gen, Radix Isatidis), whereas its aerial components can be processed into a dried bluish-spruce powder (Qing-Dai, Indigo naturalis) following dehydration for long-term preservation.
Indigo naturalis (Qingdai) is a herbal medicine extracted from the leaves or stems of various plants, including Baphicacanthus cusia (Nees) Bremek, Polygonum tinctorium, Isatis indigotica, and Indigofera tinctoria. Common synonyms and trade names for Isatis products include Ban Lan Gen, Da Qing Ye, Dyer's Woad, Folium Isatidis, Radix Isatidis, Qing Dai, Indigo Naturalis, and Woad.
In 2011, I. tinctoria root was accepted into official European phytotherapy by the introduction of its monograph in the European Pharmacopoeia. Preparations available commercially and in clinical research include dried root or leaf for decoction, standardized aqueous or ethanol extracts, granule (concentrated extract) powders, topical ointments (notably "Lindioil," an olive-oil-based formulation of Indigo naturalis), and oral capsules. In 2008, researchers optimized the formulation for Indigo naturalis and named it "Lindioil ointment," which has achieved patents in the United States, the European Union, Taiwan, China, and other countries.
2. Traditional and Historical Use
Ancient Western and European Traditions
This species was introduced into Europe in the late Prehistory and Protohistory periods, as confirmed by the discovery of textile remains dyed in blue and preserved from the Neolithic, Bronze, and Iron Ages. The ancient Egyptians used I. tinctoria as an indigo source to dye the cloth wrappings applied for the mummies.
It is thought that the Ancient Britons used woad to dye their bodies to make them look more fearsome in battle, as reported by Pliny in AD 44. In northern Europe, woad was the traditional source of indigo, and the wealth created by trading this commodity was immense, with some of the infrastructure that arose from it still apparent today in old trading centers such as Toulouse and Erfurt.
The traditional use of woad in western herbal medicine is similar to the Chinese, with the earliest known mention dating to the Hippocratic corpus (5th century BCE), where it is recommended for treating wounds, ulcers, and haemorrhoids. Dioscorides (1st century CE) recorded that the leaves of dyer's woad (Isatis sativa or I. tinctoria var. sativa) could be applied to dissolve oedema or tumours, heal bloody wounds, stop bleeding, and cure spreading ulcers, herpes, and rotten ulcers.
On one hand, the term "Isatis", which derives from the Latin "Isazein" and the Greek "Isadso," is linked to its ancient use to treat wounds. By the Renaissance, imported Indian indigo overshadowed woad dye, prices plummeted, and European woad cultivation almost vanished by the 18th century; yet traditional healers in parts of Iran and Central Asia retained local usage for respiratory issues and topical wound care.
Chinese Medicine Tradition
Isatis indigotica Fortune, a dual-purpose medicinal plant in traditional Chinese medicine, has been utilized since the Han Dynasty (206 BCE–220 CE) for heat-clearing and epidemic prevention. Its earliest medical documentation in China dates to the Theory of Medicinal Properties from the Tang Dynasty (627 AD). Indigo naturalis has been used for centuries to treat fever, hemoptysis, pediatric convulsions, oral ulcers, and sore throats.
Its root (Radix Isatidis, Chinese name Ban-Lan-Gen) and leaf (Folium Isatidis, Chinese name Da-Qing-Ye) have been widely used in combination with other Chinese medicines to treat and prevent a variety of diseases such as influenza, parotitis, epidemic encephalitis B, epidemic myelitis, epidemic cerebrospinal meningitis, acute infectious hepatitis, and sore throat.
The powdered leaf (indigo powder, Qing Dai) is used medicinally with the traditional characterization of being salty and entering the Liver, making it useful in TCM for extreme cases of heat from febrile disorders where the blood starts to move chaotically, causing nosebleeds; or when Liver fire scorches the Lungs, leading to a painful cough with blood-streaked sputum; or when Liver fire generates wind to cause convulsions, dizziness, delirium, and incoherent speech.
Over past several decades, I. indigotica has been generally utilized for its heat-clearing effects and bodily detoxification in TCM, attributed to the presence of several classes of bioactive compounds including organic acids, alkaloids, terpenoids, and flavonoids, as well as lignans, anthraquinones, glucosides, glucosinolates, sphingolipids, tetrapyrroles, and polysaccharides.
Banlangen (Ban-Lan-Gen) has been one of the eight major medicines recommended by the Chinese government for treating and preventing the deadly severe acute respiratory syndrome (SARS). The Isatis indigotica root and phenolic Chinese herbs were frequently used for the prevention of SARS during the SARS outbreaks in China, Hong Kong, and Taiwan in 2003.
Preparation Methods in TCM and Related Traditions
The root is most commonly prepared as a water decoction (Tang) by simmering in water. The roots and leaves of Isatis indigotica represent two renowned antipyretic-detoxicate crude drugs in the Chinese Pharmacopoeia, Radix Isatidis and Folium Isatidis. Indigo naturalis (Qing Dai) is a processed blue powder derived from the stems and leaves. Chinese herbal medicines containing Indigo naturalis have been used mainly as antifever and anti-inflammatory drugs, for example in the form of enema treatments for UC patients, and in Japan, Indigo naturalis powder has been sold as a health food.
3. Phytochemistry: Key Constituents and Active Compounds
The phytochemical composition of I. tinctoria has been thoroughly investigated, and the plant was proven to contain many valuable biologically active compounds, including several alkaloids — among which tryptanthrin, indirubin, indolinone — phenolic compounds, polysaccharides, glucosinolates, carotenoids, volatile constituents, and fatty acids. Over 100 compounds have been isolated across the two major species. A number of studies were carried out, and over 100 compounds were isolated over the past decades, the structures of which include alkaloids, lignans, steroids, purines, adenosine, organic acids, flavonoids, anthraquinones, and other compounds.
Lignans, indole alkaloids, and their corresponding derivatives have been identified as the major active ingredients of I. indigotica and are associated with antiviral, anti-inflammatory, anti-cancer, and other health-promoting activities.
Major Bioactive Compounds
- Indirubin: Indirubin was identified as an antileukemic drug with no inhibition of the bone marrow. Studies have revealed that indirubin and its derivatives are potent inhibitors of cyclin-dependent kinases (CDK-1, CDK-2, CDK-4, and CDK-5) and block cell proliferation by arresting the cell cycle. It has been well established that indirubin and related compounds are strong inhibitors of cyclin-dependent kinases (CDKs). Indirubin is the crucial ingredient of Danggui Longhui Wan and Qing-Dai, traditional Chinese medicine herbal formulas used for the therapy of chronic myelocytic leukemia in China for hundreds of years.
- Indigotin (Indigo): Indigotin is a blue pigment formed by dimerization of indoxyl and may exhibit mild antimicrobial properties when applied topically. The biological activity of indigotin and indirubin has been reported, and they are used as markers for quality control due to their unique pharmaceutical activities.
- Tryptanthrin: Tryptanthrin was reported to inhibit interferon-γ production by lymphocytes from Peyer's Patches, and to inhibit nitric oxide and prostaglandin E2 synthesis by murine macrophages. Evidence shows that topical Indigo naturalis significantly down-regulates the IL-17 pathway in affected skin; moreover, tryptanthrin, one of the chemical components of Indigo naturalis, possesses moderate anti-IL-17 activity — the first report associating this compound with anti-IL-17 activity.
- Isatin: A simpler oxindole alkaloid present in both leaf and root fractions; detected analytically as one of the main active components of Indigo naturalis alongside indigo and indirubin.
- Isaindigotidione: The alkaloid isaindigotidione, isolated from the roots, is a possible source of biological activity; isaindigotidione was the first compound known to contain the indolizino[7,6-c]quinoline ring system.
- Polysaccharides: Present in both root and leaf; contribute to immunomodulatory activity in laboratory models.
- Glucosinolates and their derivatives (e.g., goitrin): Characteristic of the Brassicaceae family; research interest focuses on glucosinolates (e.g., goitrin family), indirubin/indigo, tryptanthrin, and polysaccharides — primarily in lab and animal work.
- Organic acids, flavonoids, lignans: The plant contains alkaloids, organic acids, flavonoids, lignans, nucleosides, amino acids, and steroids.
Quality Markers
Through UPLC-Q-TOF-MS/MS analysis, nine common components of Indigo naturalis have been identified, including valine, isatin, tryptanthrin, indigo, indirubin, hydroxyindirubin, 5,7,4'-trihydroxy-8-methoxyflavone, isorhamnetin, and 2-(1H-indol-3-yl)acetamide.
4. Mechanisms of Action
Anti-Inflammatory Pathways
Active parts of I. indigotica — including indirubin, tryptanthrin, and lignans — reduce swelling by blocking the NF-κB pathway and helping gut bacteria stay balanced. The component indirubin was reported to inhibit cyclin-dependent kinase and signal transducer and activator of transcription-3 (STAT3) activities, and keratinocyte proliferation in vitro. In vitro, isatis leaf inhibits COX-2 with preferential effects on COX-2–catalysed prostaglandin synthesis.
Antiviral Mechanisms
The active compounds fight viruses by stopping flu viruses from copying themselves. Accumulated experimental evidence indicates that I. indigotica and related components are associated with antiviral activity against influenza A, SARS-coronavirus, foot-and-mouth disease, rabies, and human immunodeficiency virus type 1 (HIV-1), among others. In studies of Japanese encephalitis virus, I. indigotica methanol extract, indigo, and indirubin showed a concentration-dependent inhibitory effect on viral replication in vitro. Time-of-addition experiments proved potent antiviral effect by pretreatment or simultaneous treatment but not posttreatment, with antiviral action correlating with blocking virus attachment and exhibiting potent virucidal activity.
Anti-Cancer / Antiproliferative Mechanisms
Indirubin and its derivatives are potent inhibitors of cyclin-dependent kinases (CDK-1, CDK-2, CDK-4, and CDK-5) and block cell proliferation by arresting the cell cycle; the cell cycle of tumor cells treated with indirubin is arrested in the G1-S or G2-M phases, resulting in inhibition of cell proliferation followed by apoptosis. Indirubin derivatives potently inhibit Signal Transducer and Activator of Transcription 5 (Stat5) protein in CML cells.
Aryl Hydrocarbon Receptor (AhR) Activation
Indigo naturalis has been shown to ameliorate ulcerative colitis in clinical trials; furthermore, indole compounds such as indigo and indirubin, the main ingredients in Indigo naturalis, act as ligands for the aryl hydrocarbon receptor (AhR). AhR activation is thought to play a role in modulating intestinal immune responses and barrier function.
Intestinal Barrier Reinforcement
Indigo and indirubin are isomers with distinctive profiles in anti-inflammation, immune regulation, intestinal microbiota regulation, oxidative stress regulation, and intestinal mucosal repair for UC treatment. Compared with indigo and indirubin administered alone, their combination significantly reinforces intestinal barrier function by increasing the expression of E-cadherin, occludin, ZO-1, and MUC2 and improving intestinal permeability.
5. Scientific Evidence by Area of Use
5.1 Dermatology: Psoriasis
This is the most extensively studied clinical area for Indigo naturalis and Isatis-derived preparations. A systematic review included 49 studies (26 clinical trials and 23 preclinical trials). Evidence from the 26 clinical trials, involving 1,952 participants, showed that decoctions used for psoriasis treatment containing Indigo naturalis and Chinese herbal medicine formulas with Indigo naturalis as the major herb can reduce PASI, PSI, and shNAPSI scores.
Preclinical studies comprising eight animal experiments on 279 mice and 16 cell experiments involving five cell lines demonstrated that Indigo naturalis, indirubin, indigo, and tryptanthrin had anti-proliferative, anti-inflammatory, and anti-angiogenic effects in animal models of psoriasis.
The first randomized, double-blind, placebo-controlled clinical trial to evaluate the pharmacological effect of Indigo naturalis as a single topical agent (topical ointment) in Chinese patients with moderate plaque-type psoriasis found that at week 8, significant improvements in Psoriasis Area and Severity Index (PASI) scores from baseline were observed in Indigo naturalis-treated patients (56.3% had 75% improvement [PASI 75] response) compared with placebo (0.0%).
Applying a specific product containing an isatis leaf extract in olive oil (Lindioil) to the fingernails might improve nail psoriasis. The findings of the systematic review also demonstrated a higher response rate in Chinese herbal medicine formula groups than in the control group for PASI 60 (rate difference = 0.22, p < .0001).
Though clinical research has identified the efficacy of Chinese herbal medicine formulations, it has not been substantiated enough by toxicological and pharmacological studies, quality control of each component, product information of the formulas, and authentication methods. Owing to the complex composition of Chinese herbal medicine formulations, it is difficult to identify therapeutic and harmful ingredients. Due to the small size of most studies and methodological weaknesses, strong conclusions cannot be made, and the magnitudes of any effects cannot be measured with accuracy, so it is difficult to assess the clinical relevance of these preparations.
A 2025 randomized clinical trial explored a nanofibrous patch formulation. The clinical trial included 36 patients diagnosed with chronic plaque psoriasis; two symmetrical psoriatic lesions from each eligible patient were selected and randomly assigned to receive either calcipotriol ointment (control) or an Indigo naturalis–loaded nanofibrous patch for 4 weeks, with primary outcomes including PASI and secondary outcomes assessing Patient Global Assessment and safety via blood, urine, and liver/kidney function tests.
5.2 Gastroenterology: Ulcerative Colitis
Indigo naturalis is a blue pigment that has been confirmed to be highly effective for ulcerative colitis (UC) treatment in several clinical studies. Indigo naturalis has been shown to ameliorate UC in clinical trials, even suggested to be more effective than 5-aminosalicylate.
In an open-label prospective study, 20 patients with moderate UC activity were included, and capsules containing Indigo naturalis were given orally at 2 g twice daily for eight weeks. After treatment, the overall clinical efficacy was 72%, the overall clinical remission rate was 33%, and the mucosal healing rate was 61%.
In another multicenter, double-blind trial conducted in Japan, 86 patients with active UC (Mayo score) were included. The rates of mucosal healing in patients who received placebo and 0.5, 1.0, and 2.0 g of Indigo naturalis daily were 13.6%, 56.5%, 60.0%, and 47.6%, respectively, further demonstrating favorable efficacy. This evidence indicated that the clinical positioning of Indigo naturalis for UC has advantages in the remission of inflammation, especially in repairing the intestinal mucosa.
Despite these promising results, the overall evidence base has important limitations. Only two randomized controlled trials have compared Indigo naturalis with a placebo, and further studies are required to clarify the efficacy and safety of Indigo naturalis. Oral Indigo naturalis has been used in clinical trials in Asia for ulcerative colitis and other gastrointestinal conditions, but results are preliminary and severe adverse events have been reported.
5.3 Oncology: Leukemia
The bisindole indirubin has been described, for more than 30 years, as being clinically active in the treatment of human chronic myelocytic leukaemia; however, the underlying mechanism of action remained unclear for some time. Results from laboratory studies strongly suggest that inhibition of CDK activity in human tumour cells is a major mechanism by which indirubin derivatives exert their potent antitumour efficacy.
Although monomeric indirubin has been used in China for the treatment of human chronic myelocytic leukaemia, low water solubility, poor pharmacokinetic properties, and low therapeutic effects are major obstacles that have significantly limited its clinical application. Consequently, the attractive anticancer profile of indirubin has stimulated researchers to discover novel indirubin derivatives with improved pharmacodynamic and pharmacokinetic properties.
Lab studies suggest that indirubin, an active compound in isatis, stops cell duplication and therefore may be useful in cancer treatment, but studies in humans are lacking. The evidence in this area is primarily preclinical (in vitro and animal studies), and formal human clinical trials in oncology are very limited.
5.4 Antiviral Applications
Pharmacological research indicates that I. indigotica possesses antivirus, antibacterial, immunoregulatory, anti-inflammatory, and cholagogic effects. It can inhibit various viruses, such as influenza, hepatitis B, mumps, herpes simplex, cytomegalovirus, and coxsackievirus. Clinically, it is frequently used to treat various viral diseases like viral influenza, parotitis, and viral hepatitis.
Indirubin demonstrated potent in vivo protection against intracerebral Japanese encephalitis virus (JEV) challenge at a lethal dose; indirubin also regulates immunomodulatory activity on RANTES expression in influenza-infected bronchial epithelial cells, showing broad-spectrum antiviral activity and more effective virucidal action against JEV.
Other lab experiments show that isatis extract can kill certain viruses and counteract some symptoms and tissue damage from bacterial infections, but studies in humans are limited. The antiviral evidence for Isatis preparations in humans consists largely of observational use during epidemic outbreaks (SARS, influenza) in China, and controlled human trials are absent.
5.5 Atopic Dermatitis
Previous clinical trials demonstrated the efficacy and safety of Lindioil (Indigo naturalis in oil) in treating psoriasis and psoriatic nails. More recently, a randomized crossover evaluator-blinded controlled trial (published in Frontiers in Pharmacology, 2025) investigated the use of Lindioil ointment for atopic dermatitis, extending the clinical evidence base to this additional inflammatory skin condition. Evidence in atopic dermatitis is still early-stage and requires replication.
5.6 Radiation Mucositis
A small study in patients with head and neck cancer suggests that indirubin, taken as indigowood root powder, may reduce mucosal damage from radiation therapy. Additional studies are needed.
6. Body Systems and Health Areas Associated With Isatis
- Immune system: Antiviral, antibacterial, immunomodulatory activity; historical use during epidemic infectious disease outbreaks.
- Dermatological system: Psoriasis (topical and oral), nail psoriasis, atopic dermatitis, wound healing, topical infection.
- Gastrointestinal system: Ulcerative colitis, mucosal repair, gut barrier integrity, microbiome modulation.
- Haematopoietic system: Chronic myelocytic leukaemia (historically, via TCM formula Danggui Longhui Wan; indirubin as isolated CDK inhibitor).
- Respiratory system: Upper respiratory tract infections, pneumonia, sore throat, tonsillitis, laryngitis in TCM use; antiviral activity against influenza viruses in laboratory models.
- Neurological system: Historical TCM use for encephalitis and meningitis; laboratory antiviral work on Japanese encephalitis virus.
- Hepatic system: Acute infectious hepatitis in traditional use; hepatoprotective animal data.
7. Dosage Forms and Reported Dosages
Dosage information varies across preparations and clinical contexts. The following are dosages as reported in sources cited in this article:
- Oral Indigo naturalis (Qing Dai), capsules, for ulcerative colitis: In an open-label prospective study, capsules containing Indigo naturalis were given orally at 2 g twice daily for eight weeks. In a multicenter double-blind trial, doses of 0.5, 1.0, and 2.0 g of Indigo naturalis daily were studied.
- Topical Indigo naturalis ointment (Lindioil), for psoriasis: A specific product containing an isatis leaf extract called Indigo naturalis in olive oil (Lindioil) has been used safely for up to 24 weeks in topical application.
- Root decoction (Ban Lan Gen) in TCM: The typical decoction range is 9–15 g per day on a short course, with some texts listing up to 10–30 g depending on context.
- European Pharmacopoeia standardization: The root of I. tinctoria was accepted in the European Pharmacopoeia in 2011, with monograph-defined quality standards for indigo content, but specific therapeutic dosing recommendations for European use are not widely reported in the clinical literature accessed.
No universally agreed standardized dosage has been established across jurisdictions for oral therapeutic use.
8. Safety Considerations and Drug Interactions
Topical Use
Isatis is possibly safe when applied topically in an appropriate manner, short-term. A specific product containing isatis leaf extract (Lindioil) has been used safely for 24 weeks when applied to skin.
Oral Use: Adverse Events
In a Japanese nationwide questionnaire-based survey, among 877 UC patients who used Indigo naturalis (1.8% of 49,320 total surveyed), adverse events were reported in 91 patients (10.4%). Most were mild, including liver dysfunction (4.6%), gastrointestinal symptoms (2.4%), and headache (1.5%); serious adverse events such as pulmonary arterial hypertension (PAH) and intussusception were observed in 1.25% and 1.14% of users, respectively. Most cases of PAH were observed in patients treated with Indigo naturalis for more than 24 weeks, but intussusception occurred 3 to 8 weeks after initiation.
With oral Indigo naturalis: liver dysfunction, abdominal pain, nausea, and headache have been reported as adverse events. Pulmonary arterial hypertension has been associated with use of Qing Dai in patients with ulcerative colitis. Colitis involving wall thickening and edema affecting the large bowel, abdominal pain, and bloody diarrhea were also associated with its use.
The pulverized form of isatis leaf, known as Qing Dai, has been used in small studies for ulcerative colitis and showed benefit; however, its use has also been associated with pulmonary arterial hypertension, so it should not be used outside of clinical trials.
Regarding the dose of Indigo naturalis, intussusception was reported at doses of 0.5–2.0 g/day.
Drug Interactions
Indirubin, a component of the isatis plant, activates CYP3A4 gene transcription through the human pregnane receptor. Clinical relevance is not yet known. Lab studies suggest that indirubin, a component of the isatis plant, may affect how CYP450 3A4 substrate drugs are metabolized; clinical relevance has yet to be determined.
Aspirin Sensitivity
Isatis contains chemicals that are similar to the chemicals in aspirin. Isatis might trigger an asthma attack or an allergic reaction in people who are allergic to aspirin.
Pregnancy and Lactation
There is insufficient reliable information to know whether isatis is safe to use during pregnancy or breastfeeding.
Pharmacokinetic Limitations of Key Compounds
Due to low water solubility, poor pharmacokinetic properties, and low therapeutic effects, the clinical application of monomeric indirubin has been significantly limited. This has been a major driver of research into synthetic indirubin derivatives with improved absorption and efficacy.
9. Regulatory and Pharmacopoeial Status
Isatis tinctoria L. (Brassicaceae) is currently utilized more often as a medicinal remedy and also as a cosmetic ingredient. In 2011, I. tinctoria root was accepted in the official European phytotherapy by introducing its monograph in the European Pharmacopoeia. The Pharmacopoeia of the People's Republic of China, 11th edition (ChP 2020), includes monographs for both the root and leaf of I. indigotica.
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