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BackgroundLowering blood pressure (BP) by antihypertensive (AHT) drugs reduces the risks of cardiovascular events, stroke, and total mortality. However, poor adherence to AHT medications reduces their effectiveness and increases the risk of adverse events.ObjectiveTo evaluate the effectiveness of a multifactorial adherence-based intervention in a primary care setting in lowering BP.Methods/designMulticenter parallel randomized controlled trial. Thirty two nurses in 28 primary care centers of three Spanish regions. Patients aged 18–80 years, taking AHT drugs with uncontrolled BP (n=221) were randomized to a control group (usual care) or a multifactorial adherence-based intervention including nurse-led motivational interviews, pill reminders, family support, BP self-recording, and simplification of the dosing regimen by a pharmacist.Main outcome measuresThe primary outcome was 12-month blinded measure of systolic BP (mean of three measurements). The secondary outcomes were 12-month diastolic BP and proportion of patients with adequately controlled BP.ResultsOne hundred and fourteen patients were allocated to the intervention group and 109 to the control group. At 12 months, 212 (89%) participants completed the study. The systolic BP in the intervention group was 151.3 versus 153.7 in the control group (P=0.294). The diastolic BP did not differ between groups (83.4 versus 83.6). Of the patients in the control group, 9.2% achieved BP control versus a 15.8% in the intervention group. The relative risk for achieving BP control was 1.72 (95% confidence interval: 0.83–3.56).ConclusionA multifactorial intervention based on improving adherence in patients with uncontrolled hypertension failed to find evidence of effectiveness in lowering systolic BP.Trial registrationISRCTN21229328.