Isatis Leaf Classic Formulas … Natural Herb Library

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Clears heat and resolves toxin - Da Qing Ye is a classic leaf for epidemic heat, sore throat, mumps-like swelling, hot boils, and toxic febrile conditions.
Cools the blood and relieves spotted eruptions - textbook use includes high fever, agitation, macules, and rash when heat enters the blood level.
Assists with external hot swellings - fresh or prepared leaf can also be used in topical heat-toxic applications for red swollen lesions.

Xi Jiao Da Qing Tang - classic blood-heat and spotted-rash context in which Da Qing Ye helps cool the nutritive and blood levels.
Qing Wen Jie Du Wan - surface-and-interior toxic-heat formula context where Da Qing Ye helps with sore throat, fever, and epidemic heat.
Da Qing Tang with Sheng Di, Da Huang, and Sheng Ma - traditional throat-fire and oral-ulcer strategy preserved in classical references.

Official Chinese references describe Da Qing Ye as bitter and cold, entering the Heart and Stomach to clear heat, resolve toxin, cool blood, and dissipate spots.
The standard indications include warm disease with high fever, delirium, spotted eruptions, mumps, sore throat, erysipelas-like redness, and boils.
The current pharmacopoeial source is the dried leaf of Isatis indigotica, which distinguishes it from older multi-source blue-leaf traditions.