Known as daqingye or qing dai in Mandarin Chinese and as dyer's woad in English, the root of the Isatis tinctoria plant has been used in both European and Asian traditional medical systems for over 1,000 years. In Ayurvedic, Siddha, Unani and Chinese medical traditions, Isatis tinctoria is used as a treatment for the common cold as well as for mumps, sore throat, fever, sore throat, oral sores and malignant tumors. Rarely used as a single herb, the root is most commonly processed and then used in formlations including other herbs. The Chinese medicine danggui longhui wan is considered to be a specific for the treatment of chronic myelocytic leukemia, and it makes use of Isatis tinctoria root in the formulation. PC-SPES® and Prostate-Res™ are proprietary formulations from BotanicLab and ARC Nutrition, respectively, are used to treat prostate cancer, and include this herb as the primary ingredient. Despite this, the United States Food and Drug Administration has not reviewed and makes no claims as to the safety or efficacy of Isatis tinctoria in the prevention or treatment of any disease.
Alkaloid tryptanthrin, found in the plant's leaves, is thought to be responsible for a significant portion of the pharmacological activity of Isatis tinctoria. This alkaloid is thought to be a potent inhibitor of the inflammatory enyzme cyclooxygenase-2 (COX-2) and is likely responsible for the plant's fever-reducing and anti-inflammatory activity. The anti-inflammatory and anti-histaminic compounds ferulic acid and sinapic acid are also found in the leaves and may contribute to tryptanthrin's effects.
Research into the supposed anti-cancer activity of Isatis tinctoria has focused mostly on the chemical indirubin, found in the plant's roots. The compound has shown some promise as a treatment for malignant growths by inhibiting the replication of deoxyribonucleic acid (DNA) in neoplastic cells. Despite this, indirubin does not appear to produce serious bone marrow suppression. The presence of sulfurous indole molecules by the plant may also play a minor role in tumor suppression, comparable to that of other brassicas like broccoli or brussel sprouts. A more likely candidate for its tumor suppressive activity in prostatic cancers is its high concentration of the molecule beta-sitosterol.
The use of Isatis tinctoria only rarely produces side effects. Use of the purified and isolated chemical indirubin, however, has been known to produce adverse events. These include diarrhea, nausea, vomiting, lowered red blood cell count, and bone marrow suppression.