Thuppia et al. (2009) prepared an extract of banaba leaves by boiling for 2 hours which was subsequently freeze-dried. The extract was administered orally at doses up to 2000 mg/kg body weight for 12 days to streptozotocin-diabetic rats.
A dose of 1000 mg/kg decreased fasting blood glucose levels by approximately 43% on day 12, which returned to pretreatment levels by day 3 after cessation of treatment.
The banaba extract produced no changes in blood glucose levels in non-diabetic rats.
The high doses of the extract needed to produce a hypoglycemic effect may be reflected in the extraction procedure where boiling may have destroyed some of the active constituents.