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.