How can we improve adherence to blood pressure-lowering medication in ambulatory care? Systematic review of randomized controlled trials

Background: Lack of adherence to blood pressure-lowering medication is a major reason for poor control of hypertension worldwide. The objective of this study was to determine the effectiveness of interventions to increase adherence to blood pressure-lowering medication. Methods: We performed a systematic review of randomized controlled trials and searched for all-language publications in the Cochrane Controlled Trials Register, MEDLINE, EMBASE, and CINAHL in April 2002. Results: We included 38 studies testing 58 different interventions and containing data on 15 519 patients. The studies were conducted in 9 countries between 1975 and 2000. The duration of follow-up ranged from 2 to 60 months. Because of heterogeneity between studies in terms of interventions and the methods used to measure adherence, we did not pool the results. Simplifying dosing regimens increased adherence in 7 of 9 studies, with a relative increase in adherence of 8% to 19.6%. Motivational strategies were partly successful in 10 of 24 studies with generally small increases in adherence up to a maximum of 23%. Complex interventions comparing more than 1 technique increased adherence in 8 of 18 studies, ranging from 5% to a maximum of 41%. Patient education alone seemed largely unsuccessful. Conclusions: Reducing the number of daily doses appears to be effective in increasing adherence to blood pressure-lowering medication and should be tried as a first-line strategy, although there is so far less evidence of an effect on blood pressure reduction. Some motivational strategies and complex interventions appear promising, but we need more evidence on their effect through carefully designed randomized controlled trials.