Mechanism of action of natural products used in the treatment of diabetes mellitus.

Diabetes mellitus (DM) is a metabolic disorder caused by insufficient or inefficient insulin secretary response and it is characterized by increased blood glucose levels (hyperglycemia). DM is a heterogonous group of syndromes. Glucose is the main energy source for the body, and in the case of DM, management of glucose becomes irregular. There are three key defects in the onset of hyperglycemia in DM, namely increased hepatic glucose production, diminished insulin secretion, and impaired insulin action. Conventional drugs treat diabetes by improving insulin sensitivity, increasing insulin production and/or decreasing the amount of glucose in blood. This article provides a comprehensive review of the mode of action of most popular hypoglycemic herbs, such as ginseng, bitter melon, fenugreek, banaba, Gymnema sylvestre and Coptis chinensis. The herbs act by increasing insulin secretion, enhancing glucose uptake by adipose and skeletal muscle tissues, inhibiting intestinal glucose absorption and inhibiting hepatic glucose production. Although evidence from animals and humans consistently supports the therapeutic effect of these phytomedicines, multicenter large-scale clinical trials have not been conducted to evaluate the safety and efficacy of these herbal medicines and their interaction with conventional drugs when administered simultaneously.