The study intends on enrolling 48 subjects with diabetes. Diabetic subjects that no longer need insulin will be randomly placed (like the flip of a coin) on a diabetes pill called metformin, a diabetes pill called sitagliptin or a placebo pill (a pill without active medication). Subjects on pills will be followed for 3½ years and undergo blood tests at specified intervals to assess their ability to make insulin. These studies will allow a better understanding of the factors that lead to high blood sugar in patients with ketosis-prone diabetes mellitus (KPDM) and direct the best diabetes treatment for this patient population.