Background and aimsBlood pressure (BP) lowering reduces cardiovascular disease (CVD) risk; however, the benefits of treating patients with normal systolic BP but elevated diastolic BP remain uncertain.MethodsData from 51 randomized controlled trials were pooled to compare BP-lowering effects in participants with and without isolated diastolic hypertension (IDH), defined as systolic BP < 130 mmHg and diastolic BP ≥ 80 mmHg. Treatment effects were stratified across baseline diastolic BP categories (range < 60 to ≥90 mmHg) among individuals with baseline systolic BP < 130 mmHg. Fixed-effect one-stage individual participant data meta-analyses were used, and Cox proportional hazard models, stratified by trial, were applied to analyse the data.ResultsAmong 358 325 participants, 15 845 (4.4%) had IDH. At a median follow-up of 4.2 years, a 5 mmHg reduction in systolic BP reduced the risk of major cardiovascular events similarly in individuals with IDH [hazard ratio 0.91; 95% confidence interval (CI) 0.82-1.01] and those without IDH (hazard ratio 0.90; 95% CI 0.89-0.92; P for interaction = 1.00). Analyses by baseline diastolic BP showed no evidence of heterogeneity in treatment effects among individuals with baseline systolic BP < 130 mmHg (P for interaction = .26). Relative treatment effects were not statistically different by CVD history, age, prior medication use, and BP measurement methods.ConclusionsThe study found no evidence to suggest that pharmacological BP-lowering therapy in individuals with IDH is less or more effective than in those without IDH. Relative risk reductions also did not diminish in those with lower diastolic BP, down to <60 mmHg at baseline. No meaningful differences across various clinical phenotypes were detected.