This was a prospective, cluster randomized controlled trial in patients with uncontrolled hypertension aged 21 to 85 years (mean, 61 years). Pharmacists made recommendations to physicians for patients in the intervention clinics (n=101) but not patients in the control clinics (n=78). The mean adjusted difference in systolic blood pressure (BP) between the control and intervention groups was 8.7 mm Hg (95% confidence interval [CI], 4.4–12.9), while the difference in diastolic BP was 5.4 mm Hg (CI, 2.8–8.0) at 9 months. The 24-hour BP levels showed similar effects, with a mean systolic BP level that was 8.8 mm Hg lower (CI, 5.0–12.6) and a mean diastolic BP level that was 4.6 mm Hg (CI, 2.4–6.8) lower in the intervention group. BP was controlled in 89.1% of patients in the intervention group and 52.9% in the control group (adjusted odds ratio, 8.9; CI, 3.8–20.7; P<.001). Physician/pharmacist collaboration achieved significantly better mean BP values and overall BP control rates, primarily by intensification of medication therapy and improving patient adherence.