http://nccam.nih.gov/health/diabetes/
National Center for Complementary and Alternative Medicine, National Institutes of Health
There is limited scientific evidence on the effectiveness of dietary supplements as complementary and alternative medicine (CAM) for type 2 diabetes. The six dietary supplements reviewed in this report appear to be generally safe at low-to-moderate doses. However, each can interact with various prescription medications, affecting the action of the medications. People with type 2 diabetes need to know about these risks and discuss them with their health care provider. Prescribed medicines may need to be adjusted if a person is also using a complementary/alternative medicine therapy.