BACKGROUND: Even in high-performing health systems, some patients with diabetes mellitus have poor blood pressure (BP) control because of poor medication adherence and lack of medication intensification. We examined whether the Adherence and Intensification of Medications intervention, a pharmacist-led intervention combining elements found in efficacy studies to lower BP, improved BP among patients with diabetes mellitus with persistent hypertension and poor refill adherence or insufficient medication intensification in 2 high-performing health systems. METHODS AND RESULTS: We conducted a prospective, multisite cluster randomized pragmatic trial with randomization of 16 primary care teams at 5 medical centers (3 Veterans Affairs and 2 Kaiser Permanente) to the Adherence and Intensification of Medications intervention or usual care. The primary outcome was relative change in systolic BP (SBP), comparing 1797 intervention with 2303 control team patients, from 6 months preceding to 6 months after the 14-month intervention period. We examined shorter-term changes in SBP as a secondary outcome. The mean SBP decrease from 6 months before to 6 months after the intervention period was approximately 9 mm Hg in both arms. Mean SBPs of eligible intervention patients were 2.4 mm Hg lower (95% CI: -3.4 to -1.5; P<0.001) immediately after the intervention than those achieved by control patients. CONCLUSIONS: The Adherence and Intensification of Medications program more rapidly lowered SBPs among intervention patients, but usual-care patients achieved equally low SBP levels by 6 months after the intervention period. These findings show the importance of evaluating in different real-life clinical settings programs found in efficacy trials to be effective before urging their widespread adoption in all settings. CLINICAL TRIAL REGISTRATION: URL: https://clinicaltrials.gov. Unique identifier: NCT00495794.