Januvia diabetes drug, molecular model. Januvia (sitagliptin) is a hypoglycaemic drug, one that reduces blood sugar levels. Diabetes is a condition in which blood sugar levels can get dangerously high due to a lack of insulin, the hormone that reduces them. Januvia works by inhibiting the enzyme dipeptidyl peptidase-4 (DPP- 4). DPP-4 rapidly deactivates the incretin hormone GLP-1 (glucagon-like peptide 1), which promotes insulin release. Hence, inhibiting DPP-4 prolongs the effects of GLP-1, keeping insulin levels high. Atoms are colour-coded: carbon (grey), hydrogen (yellow), oxygen (red), nitrogen (blue) and fluorine (green). Januvia is marketed by Merck, and was approved in the USA in October 2006.