In Vietnam, herbal extracts have been used as a long-standing tradition to treat diabetic patients, but effects of these extracts have not been studied adequately. Based on previous results in experimental animals, we have selected the plant Gynostemma pentaphyllum (GP), which grows in the mountain region of Northern Vietnam. GP extract had a hypoglycemic effect on mice and rats, and was shown to contain a substance, phanoside, which stimulates insulin secretion. In addition, GP has been shown to reduce both hyperglycemia and hyperlipidemia in diabetic Zucker fatty rats.