**Abstract**

Cardiovascular disease is a significant cause of death globally. While effective long-term medications that reduce the risk of morbidity and mortality related to cardiovascular disease are readily available, nonadherence to prescribed medications remains a significant reason for suboptimal management. Consequently, this might lead to increased morbidity and mortality and healthcare costs. Medication nonadherence causes are myriad and complicated, with factors at the patient, healthcare provider, and health system levels. Many clinical trials have investigated interventions to target these factors for improving medication adherence, including improving patient education, testing behavioral interventions, implementing medication reminder tools, reducing medication costs, utilizing social support, utilizing healthcare team members, and simplifying medication dosing regimens. This book chapter describes factors influencing medication adherence and highlights the impact of varying levels of adherence on patients' clinical and economic outcomes. We also summarize interventions for improving medication adherence in cardiovascular disease.

**Keywords:** cardiovascular disease, medication adherence, factors, health outcomes, economic outcomes, interventions

## **1. Introduction**

Cardiovascular disease (CVD) is illnesses affecting the heart and blood vessels, including coronary heart diseases, cerebrovascular diseases, peripheral arterial diseases, rheumatic and congenital heart diseases, and venous thromboembolism [1]. CVD is a leading cause of death and disability worldwide [2]. According to the Global Burden of Diseases in 2019, CVD accounts for 15.52% of disability-adjusted life years (DALYs) and 32.84% of deaths [3].

Given the adverse health outcomes of CVD, if left untreated, long-term prevention and/or treatment of this disease is recommended. Treatment for CVD depends on its type and severity and can be divided into three main categories: lifestyle changes,

medications, and surgical procedures. Overall, lifestyle changes and medications are often recommended for chronic CVD conditions, while surgical procedures are sometimes required to treat acute CVD events such as heart attack or stroke. In recognition of the vital role of medications in CVD management, this chapter is focused on medications for treating this disease.

Despite the availability of effective CVD medications, medication nonadherence remains pervasive globally [4]. A 27% nonadherence rate in patients with acute coronary syndrome (ACS) was reported only 1 week after discharge [5]. At 1 month following ACS, 34% of patients did not fill all prescriptions [6]. At 1–2 years following ACS, the nonadherence rate reaches 55–60% [7]. Medication adherence is how patients take medication(s) as prescribed by their healthcare providers [8]. Whereas nonadherence is defined as different behaviors: not initiating a new prescription, discontinuing medication(s) early, or not taking medication(s) as scheduled (e.g. less frequently) [9]. The rate of adherence for an individual patient is usually reported as the proportion of days covered (PDC) by the prescribed medication(s) over a specific time [10]. Methods for measuring adherence include direct and indirect methods, each of which has advantages and disadvantages. Direct methods, such as observed administration or measuring the concentration of medication in the blood, are more accurate but expensive and time-consuming. Indirect methods for measuring adherence, such as patient self-reporting or pill counting, are easier to conduct but less accurate. No measurement method is gold standard, and researchers should select a method based on their targeted nonadherence behavior(s) [11].

Past studies illustrated that nonadherence to cardiovascular medications negatively influences clinical and economic cardiovascular outcomes [12, 13]. Medication adherence in CVD is challenging to manage in routine practice due to multiple factors simultaneously affecting it [4]. These factors are classified into five interactive dimensions: patient, socioeconomic, healthcare system, therapy, and condition. Various interventions have been investigated to target these factors, and some appear promising. With accumulating studies on medication adherence in CVD in recent years, the chapter thus aims to update on common factors influencing medication adherence, clinical and economic outcomes of medications (non) adherence, and interventions targeting the identified factors to improve medication adherence in CVD.
