Metformin/Sitagliptin (Janumet) is a combination of two medications, metformin and sitagliptin, used to control blood sugar in people with type 2 diabetes. Metformin decreases the amount of sugar made by the liver and improves the body's sensitivity to insulin. Sitagliptin helps the pancreas release more insulin and stops the liver from making too much sugar. Together, they can improve blood sugar levels and may also aid in weight loss.