Sitagliptin is a prescription medication that treats type 2 diabetes by increasing the amount of insulin your body produces and signaling your liver to stop producing sugar when there is too much sugar in your blood Sitagliptin is used along with diet and exercise and sometimes with other medications to lower blood sugar levels in adults with type 2 diabetes (condition in which blood sugar is too high because the body does not produce or use insulin normally). Sitagliptin is in a class of medications called dipeptidyl peptidase-4 (DPP-4) inhibitors. It works by increasing the amounts of certain natural substances that lower blood sugar when it is high.