Woad.
An ancient Chinese antiviral herb (Ban Lan Gen) used for centuries against infections and fevers. Indirubin and indigo alkaloids inhibit viral replication. Epigoitrin shows antiviral activity against influenza. Root polysaccharides stimulate innate immune response.
Reviewed March 2026
- Category
- Herb
- Also filed under
- Antiviral properties (traditional and preclinical)Anti inflammatoryTraditional fever and infection support
What Woad is, and what it does.
- Does it work
- Deep traditional evidence in TCM. Plausible antiviral mechanisms. Limited Western clinical data. If you're open to TCM approaches, it's a reasonable option for acute illness.
- How much to take
- 500-1500 mg root extract or 9-15 g dried root in decoction.
- Time to feel it
- Traditionally taken at the first sign of feeling run down, across a day or two rather than as a slow build. Nobody has timed an onset in a controlled human study.
- The first dose
- May help reduce early cold/flu symptoms if taken promptly.
- With regular use
- Used for acute illness, not daily supplementation.
- How well tolerated
- Generally well tolerated at recommended doses. Can cause GI upset at high doses. Not a substitute for medical treatment of serious infections.
- How it feels
- Bitter taste in tea form. During illness, may reduce sore throat and feverish feeling.
- The overlooked benefit
- The dye chemistry and the supplement chemistry are the same. Indoxyl precursors in the leaf oxidise in air to indigo, which is how this plant coloured cloth for centuries.
500 to 1,500mg a day is where Woad works.
Source: Chinese Pharmacopoeia; Ye & Zhang, 2011
The proof, claim by claim.
These words describe the research, not the molecule's worth. Research strength is how much work stands behind one claim, and it is never a product score.
- Antiviral against influenza
- Widely used in China for cold/flu prevention
- Reduces fever and sore throat
Questions people ask about Woad.
- Is this the same as the blue dye plant?
- Yes. The European species (Isatis tinctoria) was famous for producing blue woad dye from its leaves. The Chinese species (Isatis indigotica) is closely related. The root is used medicinally, the leaf for dye.
- Does this really work for colds?
- Chinese medicine has used it for centuries with reported success. Modern lab studies show antiviral mechanisms. Western clinical trial evidence is limited. It's not proven by Western standards, but it's deeply established in TCM.
- Where can I buy Ban Lan Gen?
- Any Chinese pharmacy, most Asian grocery stores, and online. The granule form is the most popular and convenient.
- Can I take this preventively during flu season?
- TCM generally recommends it for acute illness, not daily prevention. Some people take short courses during outbreaks, but this isn't the traditional use pattern.
Why these belong in the same formula. Each row says what the basis is, from settled biochemistry through to a trial that measured the pair.
Isatis root is rarely used alone in the tradition it comes from. Licorice is one of the herbs it is customarily combined with, partly as a taste and harmonising agent. That is a documented use pattern rather than a measured interaction. Licorice carries its own sodium and potassium handling effects that belong in any assessment of the pair.
Astragalus and Isatis root appear together in traditional multi-herb preparations aimed at seasonal use. The pairing rests on traditional formulation logic, with no combination pharmacology to cite. Nothing here establishes an additive biological effect.
Glucosinolates only become active after myrosinase from the plant or from gut bacteria cleaves them, which is the same activation step behind sulforaphane. A Brassicaceae extract such as woad therefore shares an activation dependency rather than an effect. Whether any given woad preparation retains active myrosinase depends on how it was dried and processed.
Woad root extract shows up in seasonal-use blends alongside vitamin C because of how those products are put together, not because of a shared pathway. Vitamin C has its own established role in normal immune function. No combination data exist for the pair.
Zinc is a standard component of seasonal blends that also carry botanical extracts such as Isatis root. The zinc contribution is well characterised on its own. The botanical contribution is not. Nothing about the pairing has been tested together.
Elderberry and Isatis root are used in the same product category and sometimes in the same product. The two carry entirely different phytochemistry, anthocyanins on one side and indole alkaloids and glucosinolates on the other. Co-occurrence in formulas is the whole basis, so the confidence is low by design.
Talk to a doctor before taking Woad if any of these apply to you: Limited Western clinical evidence, May cause nausea or diarrhea at high doses, Not a substitute for antiviral medications. These are flags to check first, not effects Woad is known to cause.
Not medical advice. Show the label to your pharmacist.What Woad actually does.
Woad leaves stockpile indoxyl precursors, mainly indican and isatan B. Break those down and you get indoxyl, and two indoxyl molecules meeting air turn into blue indigo. That chemistry is why the plant spent centuries as a dye.
The same indole chemistry throws off the minor pigment indirubin and the alkaloid tryptanthrin. Both are signature constituents of Isatis preparations and the ones labs most often measure as markers.
As a mustard family plant it carries glucosinolates, which sit there doing nothing until the plant's own myrosinase or a gut bacterial enzyme clips the glucose off and releases isothiocyanates and indole breakdown pieces.
In traditional Chinese practice the root and the leaf count as two separate materials with different constituent profiles, so which plant part is in the bottle is not a small detail.
Where Woad comes from.
The roots are dug in autumn, washed, sliced and dried. From there they are either sold as pieces you boil, or boiled at scale and dried into granules. What ends up in the finished product depends a lot on how gently it was dried, because the interesting compounds only form when plant enzymes act on the precursors.
Made from a plant. What ends up in the capsule tracks the harvest, so batch testing and a stated marker matter more here than with a made molecule.
A cultivated Brassicaceae biennial. Roots are typically lifted in autumn of the first or second year, leaves cut during the growing season.
Roots are washed, sliced and dried, which halts enzymatic activity and sets much of the final constituent profile. Drying temperature and speed change how much of the glucosinolate and indole fraction survives.
Traditional preparation boils the sliced root in water. Industrial extraction uses water or a water and ethanol mixture, then filters the liquor.
The filtered extract is concentrated under reduced pressure to limit thermal loss before drying.
Where a specification exists, batches are assayed against an indole marker such as indirubin or tryptanthrin, or expressed only as a plant to extract ratio.
Spray dried onto a carrier and granulated, milled to powder, or packed as sliced pieces for decoction.
Labels often omit which plant part was used, the extract ratio and solvent, whether any marker compound was assayed, and the growing region.
Getting Woad from food.
The whole-food sources on file. A supplement closes the gap, it does not replace dinner.
A gram-for-gram figure (how much of each you would eat to match a dose) will appear here once it is sourced and reviewed. This page will not print a number it cannot cite.
The forms it comes in.
The essence, in one line each.
- In 20 healthy volunteers, a woad (Isatis tinctoria) extract applied to skin during four days of sodium lauryl sulphate exposure reduced visible irritation scores and water loss through the skin compared with untreated test fields, while no effect was detected on redness after UVB exposure.Randomised trial. Heinemann et al., 2004 (Planta Medica). PMID 15124080 ↗
- A review covering the botany of Isatis tinctoria and the compounds extracted from its seeds along with their applications. It describes plant chemistry and does not report human results.Narrative review. Dupre et al., 2025 (Plants). PMID 40805652 ↗
These are the studies our verdict leans on, chosen from the 157 we read for Woad. The full linked list is below.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This information is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement regimen.