RESUMO
BACKGROUND: Primary medication non-adherence (PMN), defined as failure to obtain newly prescribed medications, results in adverse clinical and economic outcomes. We aimed to (a) assess the prevalence of PMN in six common chronic diseases: asthma and/ or chronic obstructive pulmonary disease, depression, diabetes mellitus, hyperlipidaemia, hypertension and osteoporosis; (b) identify and categorise factors associated with PMN; (c) explore characteristics that contributed to heterogeneity between studies. METHODS: We performed a systematic search in MEDLINE, Embase, Cochrane Library, CINAHL and PsycINFO. Studies published in English between January 2008 and August 2018 assessing PMN in subjects aged ≥18 years were included. We used the Cochrane risk of bias tool, Newcastle-Ottawa Scale and National Heart, Lung and Blood Institute Quality Assessment Tool to assess the quality of randomised controlled trials, cohort and cross-sectional studies, respectively. Findings were reported using the PRISMA checklist. PMN rates were pooled using a random effects model. We summarised factors associated with PMN descriptively. Subgroup analysis was performed to explore sources of heterogeneity. RESULTS: We screened 3083 articles and included 33 (5 randomised controlled trials, 26 cohort and 2 cross-sectional studies, n = 539 156), of which 31 (n = 519 971) were used in meta-analysis. The pooled PMN rate was 17% (95% CI: 15%-20%). Pooled PMN rates were highest in osteoporosis (25%, 95% CI: 7%-44%) and hyperlipidaemia (25%, 95% CI: 18%-32%) and lowest in diabetes mellitus (10%, 95% CI: 7%-12%). Factors commonly associated with PMN include younger age, number of concurrent medications, practitioner specialty and higher co-payment. Type of chronic disease, age, study setting and PMN definition contributed to heterogeneity between studies (all P < 0.001). CONCLUSION: Primary medication non-adherence is common among patients with chronic diseases and more needs to be done to address this issue in order to improve patient outcomes. Future PMN studies could benefit from greater standardisation to enhance comparability.