Predictors of nonadherence to statins: a systematic review and meta-analysis.

BACKGROUND Nonadherence to statins limits the benefits of this common drug class. Individual studies assessing predictors of nonadherence have produced inconsistent results. OBJECTIVE To identify reliable predictors of nonadherence to statins through systematic review and meta-analysis. METHODS Multiple databases, including MEDLINE, EMBASE, and PsycINFO, were searched (from inception through February 2009) to identify studies that evaluated predictors of nonadherence to statins. Studies were selected using a priori defined criteria, and each study was reviewed by 2 authors who abstracted data on study characteristics and outcomes. Relative risks were then pooled, using an inverse-variance weighted random-effects model. RESULTS Twenty-two cohort studies met inclusion criteria. Age had a U-shaped association with adherence; the oldest (>/=70 years) and youngest (<50 years) subjects had lower adherence than the middle-aged (50-69 years) subjects. Women and patients with lower incomes were more likely to be nonadherent than were men (odds of nonadherence 1.07; 95% CI 1.04 to 1.11) and those with higher incomes (odds of nonadherence 1.18; 95% CI 1.10 to 1.28), respectively. A history of cardiovascular disease predicted better adherence to statins (odds of nonadherence 0.68; 95% CI 0.66 to 0.78). Similarly, a diagnosis of hypertension or diabetes was associated with better adherence. Although there were too few studies for quantitative pooling, increased testing of lipid levels and lower out-of-pocket costs appeared to be associated with better adherence. There was substantial (I(2) range 68.7-96.3%) heterogeneity between studies across factors. CONCLUSIONS Several sociodemographic, medical, and health-care utilization characteristics are associated with statin nonadherence. These factors may be useful guides for targeting statin adherence interventions.