Januvia is a once-daily prescription pill used to lower blood sugar levels in adults with type 2 diabetes. It is taken along with a proper diet and exercise program and possibly with other medications to control high blood sugar. Januvia contains the active ingredient sitagliptin, which works by increasing levels of natural substances called incretins. Incretins help to control blood sugar by increasing insulin release, especially after a meal, and decreasing the amount of sugar your liver makes. Januvia is thought to work by slowing the inactivation of incretin hormones (GLP-1 and GIP) released by your intestine throughout the day and in response to a meal. By increasing and prolonging active incretin levels, Januvia increases insulin release from the pancreas and decreases glucagon levels and glucose release from the liver. Januvia does not typically cause low blood sugar or weight gain when used.