A study to compare safety and efficacy of sitagliptin and placebo therapy when added to
stable insulin alone or in combination with metformin in participants with type 2 diabetes
mellitus (T2DM). The primary hypothesis of this study is that after 24 weeks, the addition of
sitagliptin compared with placebo provides greater reduction in hemoglobin A1C (HbA1C) in
T2DM participants on insulin alone or in combination with metformin.