Research was conducted on type II diabetic rats to see the effects of an herbal formula (huang lian jie du tang) purporting to improve diabetes. The investigators found that it indeed decreased fasting blood glucose and serum glucose levels following an oral glucose challenge to normal levels. You need to be monitored by an herbalist when taking this formula since it can cause gastrointestinal problems if the dosage is wrong, or if other herbs are not used to mitigate the harshness. When used properly it is safe and effective.
 
Zhong Xi Yi Jie He Xue Bao. 2007 Sep;5(5):541-5.