OBJECTIVE: Treatment algorithms for type 2 diabetes recommend weight loss for disease management. The safety and efficacy of treatment with phentermine (PHEN)/topiramate (TPM) extended release (ER) plus lifestyle modification for weight loss and glycemic benefits were assessed in two randomized, double-blind, placebo-controlled 56-week studies of obese/overweight adults with type 2 diabetes. RESEARCH DESIGN AND METHODS: The OB-202/DM-230 Study was a 56-week phase 2 trial that randomized subjects to receive once-daily placebo or PHEN/TPM ER 15 mg/92 mg (15/92). The primary end point was change in HbA1c level. A post hoc analysis of a subpopulation with type 2 diabetes from a second study, CONQUER, is also presented. All subjects made lifestyle modifications, and comorbidities were managed to the standard of care. RESULTS: The study groups comprised 130 subjects with type 2 diabetes enrolled in the OB-202/DM-230 Study (mean baseline HbA1c 8.7% [72 mmol/mol]) and 388 subjects with type 2 diabetes in the CONQUER Study (mean baseline HbA1c 6.8% [51 mmol/mol]). At week 56 in the OB-202/DM-230, change in weight (from intent-to-treat sample with last observation carried forward [ITT-LOCF]) was -2.7% for placebo and -9.4% for PHEN/TPM ER 15/92 (P < 0.0001 vs. placebo). Change in HbA1c level (from ITT-LOCF) was -1.2% (-13.1 mmol/mol) for placebo and -1.6% (-17.5 mmol/mol) for PHEN/TPM ER 15/92 (P = 0.0381). In both the OB-202/DM-230 and CONQUER, greater numbers of patients randomized to receive PHEN/TPM ER treatment achieved HbA1c targets with reduced need for diabetic medications when compared with the placebo group. Common adverse events included paraesthesia, constipation, and insomnia. CONCLUSIONS: PHEN/TPM ER plus lifestyle modification can effectively promote weight loss and improve glycemic control as a treatment approach in obese/overweight patients with type 2 diabetes.