- The study is a randomized open label design. All subjects will undergo a screening visit; if inclusion and exclusion criteria are fulfilled they will be enrolled in the study. At the time of enrollment the subject will continue their home insulin regimen and will be randomized to an add an oral hypoglycemic agent(s) : metformin, sitagliptin or combination therapy (metformin and sitagliptin). The total duration on study medication will be 6 weeks. All subjects will undergo a baseline mixed meal tolerance test (MMTT) in their standard or usual insulin Each subject will undergo a total of two studies. Blood draws will be necessary.