The aim of the present study was to investigate the long-term effects on blood glucose concentrations and possible adverse effects of an extract of Gynostemma pentaphyllum (GP). This is a plant growing in the mountain regions of Northern Vietnam and previously being used in traditional medicine. The GP extract, or placebo, was randomized to newly diagnosed patients with type 2 diabetes and administered as a "tea", 3 g two times daily during 12 weeks. All patients received instructions regarding diet and physical exercise. Oral glucose tolerance tests were performed at baseline and then every 4 weeks, and blood tests were taken with the purpose to monitor lipids, kidney and liver function, body weight and blood pressure.