Berberine (BBR) is a traditional Chinese medicine used to treat diabetes mellitus for thousands of years in China. The glucose-lowering effect of BBR has been confirmed in numerous studies. Nevertheless, the detailed mechanisms of action through which BBR exerts its effects are not yet fully elucidated. In previous data, Jin-Kui Yang found that BBR could promote insulin secretion in mice and isolated islets. In this current study, investigators plan to examine the insulinotropic effect of BBR in human through hyperglycemic clamp method.