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.

Inclusion Criteria:

1. Adult healthy male, aged ≥18 and ≤45 years old.
2. Subject/ legal representative is able to understand and sign informed consent form.
3. Body mass index (BMI) 18-25 kg/m2.
4. Normal oral glucose tolerance test prior to study.
5. No family history of diabetes mellitus.
6. No medication treatment within 4 weeks prior to baseline visit and during the study.
7. Willing and able to comply with all study-related procedures, including not incorporating significant changes in diet.

Exclusion Criteria:

1. Infection with hepatitis (A, B, or C), HIV and syphilis.
2. History of allergic reaction to berberine or any component in the formulation of the study drugs.
3. Cumulative amount of blood loss (eg. blood donation) over 400mL within 3 months prior to baseline visit and during the study.
4. Alcohol drinking within 2 weeks prior to baseline visit and during the study.
5. Use of illegal drugs or positive in urine drugs screen.
6. Smoke during the study.