Sitagliptin, a Dipeptidyl peptidase-4 Inhibitor, is a medication used to treat diabetes mellitus type 2.it is taken by mouth. Metformin, is the first-line medication for the treatment of type 2 diabetes, particularly in people who are overweight. It is also used in the treatment of polycystic ovary syndrome. It is not associated with weight gain. It is taken by mouth.