Heart failure (HF) is a severe syndrome affecting more than 23 million people worldwide.¹ In spite of robust evidence demonstrating the efficacy and safety of pharmacological treatment, including different medication classes,^1,2 prognosis remains poor, particularly in advanced stages of the disease, with a 5-year survival below 35%.¹

Treatment adherence is defined as the extent to which patient behavior corresponds to healthcare professionals’ recommendations.^3-5 It is a crucial factor in the management of chronic conditions such as HF, where low adherence is associated with increased rehospitalizations and worse outcomes.^1,2,5-7 Treatment adherence is multifactorial, and it is influenced by socioeconomic factors, patient characteristics, healthcare systems, clinical conditions, and therapeutic regimens.⁴

Despite the recognized importance of appropriate medication use, gaps remain in the characterization of adherence levels across different HF populations.⁸ Furthermore, it is essential to identify modifiable factors that impact adherence in order to develop effective strategies to improve it.^6,7 Therefore, the objective of this study was to describe medication adherence levels among patients with HF followed at cardiology outpatient clinics of a specialized hospital.

This study identified a high prevalence of low adherence among patients with HF, reaching 52.6% in the "regimen" domain and 79.6% on the overall BMQ. Nearly all patients faced barriers to adherence, with the "recall" domain being the most frequently affected. Marital status (married), a history of ACS, and higher education levels were observed to be factors associated with better adherence. Additionally, in the "regimen" domain, adherence levels declined as prescription complexity increased and among patients with HFimpEF, compared to those with HFrEF.

Assessment of treatment adherence is essential to planning interventions that improve outcomes in chronic conditions.⁷ Low adherence poses an important challenge, especially in developing countries like Brazil,^4,14,15 due to resource scarcity and healthcare access inequalities.¹⁶ Reported medication adherence levels among patients with HF vary widely in the literature, ranging from 9% to 98%,^8,17 reflecting a lack of standardized measurement methods. In Brazil, few studies have been designed to describe adherence in patients with non-decompensated HF. In 2020, Farah reported a low adherence rate of 24.7%, measured via questionnaire, in 400 patients with HF using implantable electronic cardiac devices.¹⁸ In 2024, Lima et al. identified low adherence in 9.4% of a sample of 340 patients.¹⁹ Another publication with sociodemographic characteristics similar to those of the present study found a low adherence rate of 72.8%.²⁰

Better socioeconomic conditions and higher education levels have been associated with improved medication adherence across both measurement methods, suggesting that higher socioeconomic status plays a relevant and consistent role in adherence behavior. HF treatment requires multiple medications and lifestyle changes.^1,2 Patients with lower education levels are expected to face greater difficulties in understanding the complexity of the treatment and the guidance provided by healthcare professionals, which impacts appropriate self-care decision-making.^{14,15,17,21-23} In a previous study assessing the health literacy of HF patients, the majority of those facing barriers in the "regimen" domain of the BMQ had inadequate health literacy, highlighting an association between lower education level and low adherence, possibly due to a lack of understanding of the disease.^22,23 Accordingly, educational interventions are essential for both preventing adverse clinical outcomes and promoting self-care in the management of chronic diseases, particularly among patients with low health literacy.^5,24,25 A multidisciplinary team comprising physicians, pharmacists, nurses, and other healthcare professionals should be central to the care strategy; furthermore, this appears to be a cost-effective approach in diverse countries.^5,7,8,22,24

Difficulties in obtaining medications were reported by more than half of the patients in our sample, which was predominantly characterized by lower socioeconomic classes and lower monthly household income. Cost-related non-adherence is the most common cause of low adherence, influenced by monthly income and the need to pay for treatment out-of-pocket.²⁶ Large population-based studies in the United States have found a high prevalence of cost-related non-adherence, especially among individuals with chronic diseases.^27,28 In 2021, Kherallah et al. reported that this behavior was independently associated with female sex, low monthly income, and the presence of comorbidities; these characteristics were predominant in our sample. The expansion of public policies subsidizing healthcare costs proved effective in reducing low adherence rates in the United States.²⁷ Similarly, data from a population-based survey conducted in Brazil involving 11,842 individuals showed that patients with chronic conditions who received medication through the Brazilian Unified Health System (SUS) demonstrated higher adherence to drug therapy, highlighting the impact of costs on patient adherence in Brazil.¹⁴

The presence of comorbidities was associated with a higher prevalence of low adherence, although this relationship did not retain statistical significance in multivariate analyses. In patients with multiple comorbidities, polypharmacy and increased treatment complexity and costs exacerbate low adherence.^14,27,29 In an analysis of the CHARM trial involving 7,599 patients with HF, the number of comorbidities and medications was associated with worse adherence.³⁰ The number of medications and daily doses, which have been identified as a barrier in several studies,^23,29 can be reduced by means of interventions that simplify therapeutic regimens, which have shown to be effective in improving appropriate medication use.^{3,5,7,24,29,31}

Specific comorbidities, such as diabetes and atrial fibrillation, were more prevalent in the low adherence group, although multivariate analysis did not demonstrate a significant independent association. The literature on this relationship is conflicting. In 2018, Peres et al. reported worse adherence among patients with diabetes and HF, whereas Bagchi et al. associated diabetes and coronary artery disease with better adherence in 2007.^32,33 Patients with HF and atrial fibrillation have worse prognosis,³⁴ and the need for anticoagulation to prevent thromboembolic events adds complexity to treatment, impacting adherence due to concerns regarding side effects and drug interactions.³⁵ Moreover, polypharmacy is common in patients with both conditions.³⁵ Conversely, a history of ACS was a predictor of good adherence, possibly due to greater disease severity, which may raise patient awareness regarding the importance of treatment.¹⁷

Elderly patients generally face more comorbidities, polypharmacy, and a greater tendency toward forgetfulness, all of which are factors that hinder treatment adherence.^24,25 In our study, we observed no differences in adherence between sexes, which is consistent with the literature.^14,36 Mixed race and Black patients showed a higher prevalence of low adherence. The literature reiterates racial disparities in medication adherence among patients with HF,³⁷ which may be attributed to unfavorable socioeconomic conditions, lower health literacy, and greater difficulty accessing healthcare. Additionally, social support plays a crucial role in this association,^4,23,36 with studies indicating that the lack of a consistent support network is associated with worse adherence.¹⁷

Patients with HFimpEF often experience significant symptomatic improvement, which may contribute to a mistaken perception of cure and a reduced appreciation for ongoing treatment. Observational evidence has indicated that the discontinuation of disease-modifying therapies is common in this group and is associated with worse outcomes, including the recurrence of ventricular dysfunction.³⁸ Although specific data on adherence in HFimpEF remain limited, these findings support a plausible hypothesis for lower therapeutic engagement, reinforcing the need for targeted education regarding the chronic nature of the disease.

This study has some limitations. First, it has been recognized that self-report questionnaires tend to overestimate good adherence.^3,39 Consequently, the proportion of patients with good adherence found in this study may be even lower than reported. The cross-sectional study design precludes the establishment of risk or causal relationships between the variables of interest. Furthermore, a cross-sectional study does not allow for the observation of changes in adherence behavior over time or in response to potential interventions. Another point to consider is that this is a single-center study using convenience sampling, which may limit the generalizability of data to other populations and introduce selection bias due to the specific profile of patients treated at the facility. However, the sociodemographic characteristics of our sample are comparable to national Brazilian statistics, suggesting that the findings may, to a certain extent, reflect the broader reality of the HF patient population nationwide.^6,40

One of the key strengths of this study is the relevance of assessing treatment adherence in patients with HF, an essential aspect for understanding the effectiveness of the care provided at our outpatient clinic. Despite the limitations, the data obtained are highly valuable for planning comprehensive care, enabling more efficient interventions tailored to patients’ actual needs. This study's results provide an important foundation for structuring and continuously improving the outpatient service, enabling the development of strategies to enhance the quality of care and patient monitoring, with the aim of positively impacting clinical outcomes.

The prevalence of low adherence to drug therapy among patients with HF was a significant issue in our sample. This behavior is influenced by socioeconomic determinants, social support, polypharmacy, and factors related to patients’ clinical conditions. These findings underscore the need to promote health education and to implement strategies that simplify therapeutic regimens whenever possible. Furthermore, they provide valuable insights for optimizing the quality of care provided in outpatient settings, with the aim of improving adherence and clinical outcomes.