Introduction
Patients’ adherence to treatment is important to maximize the benefit of healthcare provided to patients and is a key factor in a variety of subsequent health outcomes. We understand adherence to treatment as the process in which the patient engages in a health, technology or medication treatment that was agreed upon together with a healthcare professional. Adherence includes meeting the following conditions that are relevant to the treatment: (1) Taking prescribed medication correctly at the minimum clinical threshold agreed upon, including initiation, dosage, and persistence; (2) Carrying out recommended health behaviours, such as attending follow-up appointments, and/or implementing lifestyle changes (e.g., avoiding certain foods or engaging in specific exercise), at the minimum clinical threshold agreed upon.
Currently, lack of adherence is associated with personal suffering, poorer health outcomes, and a significant burden on healthcare costs/budgets (Cutler et al., 2018). Overall, up to 125,000 premature deaths per year in the US (Martin et al., 2014) and 200,000 in the EU (OECD & European Union, 2018) can be related to non-adherence. On average, 25 percent of patients do not engage in recommendations for prevention and disease management activities, including medication intake, technical treatment modalities (e.g., positive airway pressure [PAP]), appointment scheduling, screening, exercise, and dietary changes (DiMatteo, 2004; Dobler, 2021). More general estimates show that almost 50 percent of patients do not adhere to treatment recommendations (Anglada-Martinez et al., 2015). When preventive or treatment regimens are complex and/or require lifestyle changes and modification of existing habits, non-adherence can be as high as 70 percent (Chesney et al., 2000; Dobler, 2021). Treatment non-adherence has been identified as a major barrier to the effective (self-)management of chronic conditions, leading to poorer health outcomes among patients, higher hospitalization rates, and increased mortality. Therefore, non-adherence eventually causes an additional financial burden on healthcare systems and the overall social costs (Cutler et al., 2018; Kim et al. 2019).
Given the proportion of the patient population that does not adhere to treatments, efforts to improve treatment adherence represent a great opportunity to enjoy the full benefit of treatment and enhance health outcomes while ensuring quality, efficiency, and sustainability of the healthcare system. Action to better understand the complexity of factors that influence patients’ capacities and the reasons driving behaviour change towards treatment adherence is urgently needed to address the situation, focusing on “real individuals ” instead of the “ideal individuals ” (Bavel et al., 2020). Therefore, for effective care provision, it is necessary to activate the patient and the patient’s community of support to better understand the complexity of factors and improve adherence to treatment. The main aim of this systematic review (SR) is to understand the state of the art of scientific evidence about the relationship and impact of different types of interventions developed to increase adherence to treatment.