Indirubin is a chemical constituent of indigo naturalis (also known as qing dai 青黛), which has been used since 627 AD in traditional Chinese medicine.

It is essentially the indigo dye as traditionally extracted from plants by fermentation and lime treatment.

[1] The dye mixture contains a variety of organic compounds, indirubin and tryptanthrin being possible sources of some pharmacological actions.

[1] Indirubin exerts its effects on the human body by downregulating expression of genes.

Indirubin has, in vitro and in vivo, been shown to reduce expression of the CDC25B gene, which codes for production of CDC25B enzyme.