How does metformin help control glucose levels?

In December 1994, metformin (Glucophage) was approved for use by the Food and Drug Administration. It belongs to a class of drugs called the biguanides. Biguanides work differently than sulfonylureas. During times you are fasting, such as overnight, your liver releases glucose so that your cells have the energy they need. Biguanides lower blood glucose mainly by putting a brake on the liver’s release of stored glucose. They also hinder the absorption of glucose from food being digested in the small intestine. Biguanides may also lower insulin resistance in the muscles. Because metformin acts to decrease glucose release rather than increase insulin activity, there is little risk of very low blood glucose levels (hypoglycemia). Metformin has the added advantages of helping lower high blood lipid levels and promoting weight loss.