The carcinogen aristolochic acid, which was found in many prescribed Chinese herbal products including Guan Mu Tong, is associated with an increased risk of urinary tract cancer, according to a new study published online December 21 in the Journal of the National Cancer Institute. Many countries, such as Taiwan, have banned products containing aristolochic acid (Taiwan did in 2003), because of clinical cases of urothelial cancer in association with aristolochic acid use... 
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