A review on natural products for controlling type 2 diabetes with an emphasis on their mechanisms of actions.

The use of natural products is very common among non-industrialized societies because these remedies are more accessible and affordable than modern pharmaceuticals. In developed countries, use of herbal products has recently increased as scientific evidence about their effectiveness has become broadly available. For the past two decades many research articles in the field of ethno-pharmacology have focused on the anti-diabetic effects of some natural products. This dramatic increase of interest was partly due to the fact that type 2 diabetes mellitus (T2DM) was considered as becoming a global epidemic health problem which imposed high cost to national health services around the world. We have no intention to advocate for replacing conventional pharmacotherapy with natural products to prevent and control T2DM. However, the fact that a lack of highly effective drug-therapy with existing synthetic agents and their resulting adverse effects motivated further search into traditional medicine in order to re-evaluate old remedies as well as screening to find new natural entities to be used as anti-diabetic products cannot be ignored. Some recent reports on the natural products with anti-diabetic effects have provided evidence for possible mechanisms of action. Nonetheless, the majority of investigators only speculated on a wide range of possible mechanisms or simply demonstrated an anti-hyperglycemic effect for the crude plant extracts or the isolated compounds of interest. A few reviews with less attention paid to mechanisms of action have been published on medicinal plants and diabetes. This article reviews publications on anti-diabetic natural products that have appeared in PUBMED or other research-related literature found on the Internet (from 1990 to present) to categorize them based on their mechanisms of action. We hope that this communication will be beneficial as a starting point to consider the discussed products for further investigations to identify and develop new remedies with potential alternative or complementary use in controlling T2DM.