OBJECTIVES: To characterize, classify and prioritize the barriers to medication adherence across multiple disease states to enhance researchers’ and providers’ understanding and decision-making using real world evidence.

METHODS: A targeted literature review was initially conducted for 5 disease areas: oncology, diabetes, asthma, rheumatoid arthritis (RA), and multiple sclerosis (MS). Search terms included adherence, barriers, facilitators, and interventions; time-frame was 6 years (2014-2019). The focus was on selection of primary research publications and systematic literature reviews. Data was extracted by 2 independent researchers into an Excel spreadsheet. Barriers were categorized using the World Health Organization (WHO) 2003 classification scheme and ranked based on reported prevalence in identified studies. The 5 dimensions of adherence specified by the WHO are 1) social & economic, 2) healthcare system, 3) condition-related, 4) therapy-related, and 5) patient-related.

RESULTS: A total of 194 publications were reviewed and 28 were selected for abstraction in oncology, 20 in diabetes; 42 in asthma; 14 in RA; and 24 in MS. The most prevalent barriers to adherence barriers were identified initially for oncology and MS. For oncology, key barriers to adherence were employment/poverty status & income level, insurance coverage, health & medication beliefs, psychological stress, forgetfulness, drug type, and adverse effects (actual/perceived). For MS, key barriers identified were adverse effects of the medication, forgetfulness, drug effectiveness, and depression/emotional problems.

CONCLUSIONS: This research demonstrates the disparity in barriers studied and reported across different disease states. Potential reasons for this variation may range from the underlying disease state, to study design, to ease of reporting individual barriers. These results warrant the need for a systematic classification of medication adherence barriers to enable evaluation and prioritization across multiple disease states, and a means to ameliorate identified barriers via interventions to enhance and optimize patient outcomes.