Background: Evidence on the time course of antihypertensive drug (AHTD) efficacy is crucial to guide the frequency of visits recommended in guidelines and when it is appropriate to wait for further effects to accrue. Objective: To assess how quickly AHTD therapy works to lower blood pressure (BP). Methods: We systematically searched multiple electronic databases for relevant randomized, double-blind, placebo-controlled trials of untreated adults. These trials compared fixed doses of AHTDs from the five major classes to a placebo for a minimum of four weeks and reported BP data at baseline, and at least at weeks 2 and 4. Primary outcomes were systolic and diastolic BP reduction at weeks 2, 4, and 8. A fixed-effect meta-analysis was conducted, and a best-fit exponential association model was used to evaluate BP-lowering efficacy over time. Results: A total of 94 trials (25,637 participants) were included. Trial duration ranged from 4-16 (median 8) weeks. The best-fit exponential association model predicted that the reductions in systolic BP (SBP) at weeks 1, 2 and 3 were 64%, 79%, 85% of the reductions seen at week 4. There was no evidence of additional BP reduction after week 4. In absolute terms, after week 2 the additional reduction in BP averaged only 1.8/0.8 mmHg by week 4 and 0.4/0.2 mmHg between week 4 and week 8. This finding was consistent across trials by drug class, with no evidence that renin-angiotensin-aldosterone system inhibitors, diuretics, beta-blockers, calcium channel blockers, diuretics or combinations took longer to work. Baseline BP did appear to modify the effect, but still there was no additional benefit after 4 weeks. Conclusion: BP lowering drugs work quickly, with little additional BP lowering occurring after 2 weeks. These findings have relevance for guidelines and for addressing treatment inertia related to expectation of time needed for drugs to work fully.
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