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.

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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.

How to take it

TimingTiming does not matter; traditional use is short courses during an acute illness.

With food?With food, which reduces the common stomach upset.

Worth knowingDo not take it continuously as prevention — Chinese regulators specifically warn against that pattern of use.

Frequently asked questions

Does isatis root (ban lan gen) work for colds or flu?

The evidence for isatis root is limited. Research is dominated by in-vitro and animal studies, and no trial has shown that ban lan gen shortens or prevents influenza in people.

Can I take ban lan gen every day to prevent colds?

No. Chinese regulators specifically warn against continuous preventive use of isatis root; traditional use is short courses during an acute illness.

Does isatis root have side effects?

Isatis root is generally tolerated short-term, but stomach upset is common, and allergic reactions and, rarely, haemolysis have been reported with high-dose ban lan gen granules. Avoid it in pregnancy and in children without medical advice.

How much isatis root should I take?

No supplement dose of isatis root is validated. Traditional decoction use is 9–15 g of dried root per day, and granule products follow their own labels; taking it with food reduces stomach upset.

Scientific references

Isatidis Radix and Isatidis Folium: A systematic review on ethnopharmacology, phytochemistry and pharmacology
Chen J, Zhu Z, Gao T, Chen Y, Yang Q, Fu C, Zhu Y, Wang F, Liao W — J Ethnopharmacol, 2022
Antiviral activity of Isatis indigotica root-derived clemastanin B against human and avian influenza A and B viruses in vitro
Yang Z, Wang Y, Zheng Z, Zhao S, Zhao J, Lin Q, Li C, Zhu Q, Zhong N — Int J Mol Med, 2013

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Herbal medicines: what the evidence says (335)