Prevalence of and factors associated with primary medication non‐adherence in chronic disease: A systematic review and meta‐analysis

Interest in patient adherence has increased in recent years, with a growing literature that shows the pervasiveness of poor adherence to appropriately prescribed medications. However, four decades of adherence research has not resulted in uniformity in the terminology used to describe deviations from prescribed therapies. The aim of this review was to propose a new taxonomy, in which adherence to medications is conceptualized, based on behavioural and pharmacological science, and which will support quantifiable parameters. A systematic literature review was performed using MEDLINE, EMBASE, CINAHL, the Cochrane Library and PsycINFO from database inception to 1 April 2009. The objective was to identify the different conceptual approaches to adherence research. Definitions were analyzed according to time and methodological perspectives. A taxonomic approach was subsequently derived, evaluated and discussed with international experts. More than 10 different terms describing medication-taking behaviour were identified through the literature review, often with differing meanings. The conceptual foundation for a new, transparent taxonomy relies on three elements, which make a clear distinction between processes that describe actions through established routines ('Adherence to medications', 'Management of adherence') and the discipline that studies those processes ('Adherence-related sciences'). 'Adherence to medications' is the process by which patients take their medication as prescribed, further divided into three quantifiable phases: 'Initiation', 'Implementation' and 'Discontinuation'. In response to the proliferation of ambiguous or unquantifiable terms in the literature on medication adherence, this research has resulted in a new conceptual foundation for a transparent taxonomy. The terms and definitions are focused on promoting consistency and quantification in terminology and methods to aid in the conduct, analysis and interpretation of scientific studies of medication adherence. © 2012 The Authors. British Journal of Clinical Pharmacology © 2012 The British Pharmacological Society.

The aim of this cross-sectional study was to quantify patients' personal beliefs about the necessity of their prescribed medication and their concerns about taking it and to assess relations between beliefs and reported adherence among 324 patients from four chronic illness groups (asthma, renal, cardiac, and oncology). The findings revealed considerable variation in reported adherence and beliefs about medicines within and between illness groups. Most patients (89%) believed that their prescribed medication was necessary for maintaining health. However, over a third had strong concerns about their medication based on beliefs about the dangers of dependence or long-term effects. Beliefs about medicines were related to reported adherence: higher necessity scores correlated with higher reported adherence (r=0.21, n=324, p<0.01) and higher concerns correlated with lower reported adherence (r=0.33, n=324, p<0.01). For 17% of the total sample, concerns scores exceeded necessity scores and these patients reported significantly lower adherence rates (t=-4.28, p<0.001). Stepwise multiple linear regression analysis showed that higher reported adherence rates were associated with higher necessity-concerns difference scores (beta=0.35, p<0.001), a diagnosis of asthma (beta= -0.31, p<0.001), a diagnosis of heart disease (beta=0.19, p<0.001), and age (beta=0.22, p<0.001). Gender, educational experience, or the number of prescribed medicines did not predict reported adherence. Medication beliefs were more powerful predictors of reported adherence than the clinical and sociodemographic factors, accounting for 19% of the explained variance in adherence. These data were consistent with the hypothesis that many patients engage in an implicit cost-benefit analysis in which beliefs about the necessity of their medication are weighed against concerns about the potential adverse effects of taking it and that these beliefs are related to medication adherence.