Januvia (sitagliptin) is a prescription medication that helps lower blood sugar in adults with Type 2 diabetes. It works best when you also follow a balanced diet and exercise regularly. It belongs to the drug class called dipeptidyl peptidase-4 (DPP-4) inhibitors, or gliptins. Januvia (sitagliptin) comes as a tablet you take by mouth once a day. Side effects include stuffy or runny nose and headache. Januvia (sitagliptin) is a brand-name medication only; the generic version isn't available yet.