The hypoglycemic (blood sugar-lowering) action of gymnema leaves was first documented in the late 1920s. This action is attributed to members of a family of substances called gymnemic acids. Gymnema leaves raise insulin levels, according to research in healthy volunteers. Based on animal studies, this may be due to regeneration of the cells in the pancreas that secrete insulin, or by increasing the flow of insulin from these cells. Other animal research shows that gymnema can also reduce glucose absorption from the intestine, improve uptake of glucose into cells, and prevent adrenal hormones from stimulating the liver to produce glucose, thereby reducing blood sugar levels.
Other animal studies have shown that extracts of gymnema leaves can lower serum cholesterol and triglycerides and prevent weight gain, but these effects have not been tested in humans. When placed directly on the tongue, gurmarin, another constituent of the leaves, and gymnemic acid have been shown to block the ability in humans to taste sweets.