Supplement analysis backed by scientific evidence · PT

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Limited evidenceImmunity

Isatis Root (Ban Lan Gen)

A hugely popular over-the-counter cold remedy in China, sold mainly as granules. Its reputation rests on tradition and laboratory antiviral work rather than on controlled trials.

Evidence last reviewed: August 2026

What the science says

  • Popular use far outruns the evidence Limited evidence

    A systematic review of Isatidis Radix and Folium covering ethnopharmacology, chemistry and pharmacology found the research base dominated by in-vitro and animal studies, with very few adequately controlled human trials for its main cold and sore-throat indication.

  • Antiviral activity only in cell culture Limited evidence

    Clemastanin B isolated from Isatis indigotica root inhibited human and avian influenza A and B viruses in cell culture. No trial has shown that taking the root shortens or prevents influenza in people.

Dosage & safety

Studied doseNo validated supplement dose. Traditional decoction use is 9–15 g of dried root per day; granule products follow their own labels.
SafetyGenerally well tolerated short-term, but allergic reactions and, rarely, haemolysis have been reported with high-dose banlangen granules, and Chinese regulators warn against continuous prophylactic use. Gastrointestinal upset is common. Avoid in pregnancy and in children without medical advice.

Scientific references

Where to buy

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