The association of depression with adherence to antihypertensive medications: a systematic review

To examine the strength and consistency of the evidence on the relationship between depression and adherence to antihypertensive medications. The MEDLINE, CINAHL, PsycINFO, Embase, SCOPUS, and ISI databases were searched from inception until 11 December 2009 for published studies of original research that assessed adherence to antihypertensive medications and used a standardized interview, validated questionnaire, or International Classification of Diseases Ninth Revision code to assess depression or symptoms of depression in patients with hypertension. Manual searching was conducted on 22 selected journals. Citations of included articles were tracked using Web of Science and Google Scholar. Two investigators independently extracted data from the selected articles and discrepancies were resolved by consensus. Eight studies were identified that included a total of 42,790 patients. Ninety-five percent of these patients were from one study. Only four of the studies had the assessment of this relationship as a primary objective. Adherence rates varied from 29 to 91%. There were widely varying results within and across studies. All eight studies reported at least one significant bivariate or multivariate negative relationship between depression and adherence to antihypertensive medications. Insignificant findings in bivariate or multivariate analyses were reported in six of eight studies. All studies reported statistically significant relationships between depression and poor adherence to antihypertensive medications, but definitive conclusions cannot be drawn because of substantial heterogeneity between studies with respect to the assessment of depression and adherence, as well as inconsistencies in results both within and between studies. Additional studies would help clarify this relationship.