Januvia is used to improve glycemic control in adults with type 2 diabetes. It should not be used for type 1 diabetes or diabetic ketoacidosis, as it would not be effective.
Full prescribing information is available at:
http://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=9347
Check out Wikipedia for more user-friendly information:
http://en.wikipedia.org/wiki/Januvia