The purpose of this study is to compare the effectiveness and safety of topiramate with placebo in the treatment of obesity and Type 2 diabetes mellitus in patients who have failed on sulfonylurea therapy.

Topiramate is a medication for the treatment of seizures, but not approved for the treatment of obesity. This is a randomized, double-blind, placebo controlled study to evaluate the effectiveness and safety of topiramate in Type 2 diabetic patients with obesity who have failed on treatment with sulfonylurea. After a 4-week enrollment phase and 8-week titration phase, patients receive either topiramate (96, 192, or 256 mg twice daily) or placebo for 44 weeks, followed by a 6-week follow-up phase. Assessments of effectiveness include body weight, hemoglobin type A1c [HbA1c] (a measurement of average blood sugar level over several months), Body Mass Index (BMI), fasting plasma glucose (FPG) level, fasting lipid profile, fasting insulin, uric acid level, blood pressures, and health related quality of life (HRQOL) measures. Safety evaluations, including incidence and severity of adverse events, hypoglycemic epidoses, clinical laboratory results such as the liver enzymes, and vital signs, are performed throughout the study. The study hypothesis is that topiramate will be effective in the treatment of type 2 diabetes through weight reduction.

During the initial 8-weeks, oral doses taken twice daily of topiramate or placebo will be gradually increased to target doses (either 96 milligrams[mg], 192mg, or 256mg daily); the dose will be maintained for 44 weeks.

• Diabetes Mellitus, Adult-Onset
• Diabetes Mellitus, Type 2
• Obesity

Inclusion Criteria: - Diagnosis of Type 2 Diabetes, receiving only second generation sulfonylurea therapy (may include: glipizide, gliclazide, glimepiride, glibenclamide/glyburide, and gliquadone) for at least 4 months and on stable dose for at least 2 months - Body Mass Index >= 27 and < 50 - HbA1c < 11% at enrollment - Diagnosed hypertension or hyperlipidemia must be controlled - Female patients must be postmenopausal for at least 1 year, surgically incapable of childbearing, practicing an acceptable method of contraception (requires negative pregnancy test)

Exclusion Criteria: - Known contraindication or hypersensitivity to topiramate or sulfonylurea therapy - Pregnancy or women who are nursing or plan to become pregnant during the study - Diagnosed with Type 1 diabetes - History of severe or recurrent hypoglycemic episodes - Treatment with any antidiabetic agent other than sulfonylurea