Which is the best beta blocker? Inositol is another supplement that may work as a natural beta blocker by calming the body and relieving anxiety and stress. . Both garlic and onion contain juices that, when broken down by the acid in your stomach, can. Although the exact mechanism of metformin that causes diarrhea and other gastrointestinal side effects is still unclear, researchers have developed several possible explanations, including stimulation of intestinal secretion of serotonin, alteration in incretin and metabolism of glucose, and malabsorption of bile salts.