a) Definition

There are different definitions of «therapeutic adherence», as mentioned by Pisano ⁽⁹⁾. Names such as adherence, therapeutic adherence, compliance, obedience, concordance, therapeutic alliance, willingness to improve the management of one’s own health or adherence, among others, are used.

In the development of this concept and to understand its complexity, it must be considered that adherence is a complex and multifactorial phenomenon, because it involves a great variety of situations (taking medication, going to appointments, risk behaviors, the environment family, socio-economic level, etc.), and it is not a behavior that is permanent, because it may or may not occur temporarily, since therapeutic adherence implies a relationship centered on the needs of the person, in which there is to consider her values and knowledge, inform her adequately and respect the choice of her therapeutic alternatives; In other words, it is necessary to migrate from the paternalistic model, in which the patient does not have active participation, to a model of shared decisions. Therefore, it is considered an error to hold a patient responsible as non-compliant or non-compliant, attributing exclusively responsibility for a problem as complex and multifactorial as therapeutic adherence ⁽⁹⁾.

In 1985, according to Jay ⁽¹⁰⁾, the terms «adherence» and «compliance» could be used interchangeably with «compliance»; and he defined the latter as the extent to which a person’s behavior (in terms of taking medications, following diets or making lifestyle changes) coincides with medical or health advice. In 2007, DiMatteo ⁽¹¹⁾ defined «patient adherence» as following medical treatment recommendations prescribed by a physician. This author mentions that other similar terms can be used, such as: adherence, compliance, follow-up, continuation of treatment and acceptance of medical recommendations.

On the other hand, Conthe ⁽¹²⁾ uses the term «compliance» and defines it as the extent to which the patient assumes the rules or advice given by the physician or other health professional, both from the point of view of habits or lifestyle, as well as the prescribed pharmacological treatment itself, and which expresses the degree of coincidence between the guidelines given by the health professional and those carried out by the patient, following a fully reasoned decision by the latter.

Some health systems, such as the National Health Services of the United Kingdom ⁽¹³⁾, define adherence as the extent to which the patient’s behavior coincides with the recommendations agreed by the prescriber. In its 2005 annual report, it emphasizes that it has adopted this term in an attempt to emphasize that the patient is free to decide whether to adhere to the prescriber’s recommendations, and that failure to do so should not be a reason to blame the patient.

Given the different definitions and complexity of the term adherence, the World Health Organization (WHO), in an effort to unify, and at the same time simplify the understanding of this concept, defines «therapeutic adherence» as the degree to which the behavior of a person -taking the medicine, following a diet and making lifestyle changes- corresponds to the recommendations agreed by a healthcare provider⁽²⁾.

b) Implications of lack of adherence

The immediate impact of non-adherence is clinical, but also economic and social, so its effects are observed at two levels: the first, directly on the patient and their family, and the second, at the sanitary level systems. Regarding the impact on the patient, the obvious affectations are the clinical ones. The degree of these affectations will depend in the first place on whether a treatment is started or not when the disease is detected, since, even if said treatment is not started, what will be observed in the patient’s health will be the clinical conditions of the natural disease, which, in the medium or long term and depending on the type of disease, will cause the consequences of the deterioration to be irreversible and even fatal. In the event that treatment is interrupted or partially followed, it will depend on the severity and chronicity of the disease whether the patient deteriorates to a greater or lesser degree ⁽¹⁴⁾.

On the other hand, the lack of therapeutic adherence can cause inadequate evaluations of the real effectiveness of the medication, which can lead to prescribe more drugs and modify the doses, causing major alterations in the patient’s condition, thus reducing the effectiveness of the treatments and the probability of therapeutic success ⁽¹²⁾.

In health systems, the economic and social consequences of no or low therapeutic adherence are mainly: higher costs of drugs that are taken inappropriately or not even used; an increase in days and duration of hospitalizations, as well as in emergency room admissions; complementary tests and use of other drugs, all of which translate into a considerable increase in costs for the health system or, even, for the direct cost of the patient ⁽², ¹²⁾. In other words, exclusively clinical interventions and investments aimed at disease control have a low return in primary care (disease prevention) and secondary care (disease control) ⁽¹⁵⁾. In view of the above, it is of utmost importance to highlight Neiman’s statement ⁽¹⁶⁾: improving adherence is a public health priority and could reduce the economic and health burden of many chronic diseases and conditions.

c) Factors that influence therapeutic adherence and its management

As Amy Hai comments, non-adherence is a complex set of behaviors, which always begins to be analyzed at the patient level, and here it can be said that there are both intentional and unintentional causes. Unintentional non-adherence occurs when the patient wants to adhere but is unable to do so because he or she lacks capacity or resources; for example, lack of understanding of instructions or forgetting the treatment. Intentional nonadherence occurs when the patient decides not to follow the recommendations, a situation that could be better understood in terms of the factors of perception, beliefs, and preferences that influence the motivation to start and continue with treatment ⁽¹⁷⁾.

According to Conthe, it has been possible to define a profile of the non-compliant patient: the most frequent cause of non-compliance is forgetting to take the medication; the lack of health education about the disease; the complexity of the treatment received; the inadequate doctor-patient relationship; the lack of knowledge about the use of the medication; the appearance of adverse reactions; and the lack of social and family support. Elderly patients are the biggest consumers of drugs, and are a group particularly susceptible to very low levels of therapeutic adherence ⁽¹²⁾.

It is important to mention that barriers to behavior change vary depending on the chronic disease or comorbidities; for example, according to Burges ⁽¹⁵⁾, it was found that in overweight patients the main barriers include lack of motivation; environmental, social and family pressures; lack of time; physical and health limitations; negative thoughts/moods; socioeconomic limitations; gaps in knowledge/awareness and lack of enjoyment of exercise, while for adherence in diabetes, patients’ attitude, cultural beliefs and knowledge about diabetes significantly affect the control of this disease ⁽¹⁸⁾.

d) Socioeconomic factors

Although socioeconomic status has not been systematically found to be a predictor of adherence, in developing countries, low socioeconomic status can place patients in the position of having to choose between the priority of attending to their health or their basic needs, such as attending to the needs of the children or parents they care for ⁽²⁾. In addition to the above, it has been observed that socioeconomic levels classified as poverty levels go hand in hand with illiteracy, low educational level, unemployment, lack of effective social support networks, unstable living conditions, remoteness from the treatment center, high cost of transportation, cost of medication that makes it unaffordable, changing environmental situations, culture and popular beliefs about the disease, treatment and family dysfunction ⁽⁷, ¹⁹⁾.

In recent years, adherence research has focused on patients’ obstacles to adherence. In this perspective, the physician’s responsibility for optimizing adherence to treatment was not considered important, but research in recent years has shown that the lack of adherence is multifactorial. Physicians have been identified as playing a central role because, if they do not effectively communicate basic information about treatment plans and their importance to their patients, patients may be left with concerns about adverse drug effects and a lack of understanding of the disease and treatment, which negatively affect their adherence ⁽¹⁸, ²⁰⁾. Lack of health education has also been identified as a central factor negatively affecting adherence ⁽²¹⁾. The impact of this lack of health education is observed in socially disadvantaged patients as well as in those without socioeconomic problems, which could explain why chronic diseases have become a worldwide problem at all levels ⁽²²⁾.

Various multifactorial analyses have identified factors that affect therapeutic adherence ⁽⁸, ¹², ¹⁸, ¹⁹, ²⁰, ²³, ²⁴, ²⁵⁾: some of them are listed and grouped below.

Of the above factors, two are crucial: the health professionals and the family environment. Poor adherence cannot be framed only in terms of the fears and ignorance of patients, who obviously decide for themselves; it is also a responsibility of health professionals to generate adequate and effective communication with the patient to adequately address his or her disease and concerns ⁽²⁰⁾. However, the lack of knowledge of physicians to identify and manage the psychological well-being of patients has been documented, and some studies have even identified that physicians themselves acknowledge that they lack effective communication tools and skills in counseling and shared decision making ⁽¹⁸⁾.

Taking the above into consideration, and according to the WHO ⁽²⁶⁾, health professionals should be specifically trained in achieving patients’ therapeutic adherence, since they can have a significant impact by assessing the risk of non-adherence and intervening in a timely manner to optimize it. However, this is not simply because they are physicians and have clinical knowledge; to achieve this effectiveness in their interventions, health professionals must have access to specific training in adherence care ⁽²⁴⁾, since even physicians’ attitudes toward diabetes management may be more important than their actual knowledge of the disease. This training should have three main focuses: knowledge (information on adherence), reasoning (the clinical decision-making process), and action (behavioral tools for health professionals) ⁽¹⁸⁾. Patients should be active partners with health professionals in their own care, and such good communication between the two is an essential requirement for effective clinical practice ⁽¹⁴⁾.

Regarding family support, the WHO also mentions that it is a key factor for success in improving therapeutic adherence, since they play an active role in the daily routine of patient care, in accompanying the patient in understanding the disease, which impacts on health outcomes and patient behavior, since some studies have even shown that this active participation of the family is reflected in health professionals reducing the time dedicated to the care of chronic patients ⁽²⁾.

As for healthcare systems, according to Horne ⁽¹³⁾, current levels of noncompliance imply an inability to address patients’ needs and preferences, and represent a fundamental inefficiency in the delivery and organization of services, and that increasing the effectiveness of adherence interventions can have a much greater impact on population health than any improvement in specific medical treatments, yielding benefits such as: better care tailored to patient needs, higher rates of adherence to appropriate medication, fewer unwanted and unused prescriptions, more effective chronic disease management, greater patient safety and satisfaction, and fewer emergency admissions.

e) Measurement

For the management of chronic diseases, it is important and necessary to routinely assess therapeutic adherence in patients during their treatment. In order to be able to assess adherence, direct or indirect techniques are used. The direct ones can be the determination of the drug or its metabolites in blood, urine or other biological fluid, clinical parameters determined through laboratory studies. Meanwhile, the indirect ones consider the counting of tablets, attendance at scheduled appointments, assessment of therapeutic efficacy, assessment of side effects, electronic monitoring of medication and clinical interview techniques, which are based on directly asking the patient about his compliance or are self-reporting questionnaires ⁽²⁾. The latter method is recommended because of its ease of application and because it does not involve any cost; but it is necessary to recognize that there is no instrument that can be considered the «gold standard», so that, in order to select the instrument to be used, the disease, the population and its characteristics, as well as the dimension of adherence to be evaluated, should be considered ⁽¹², ²⁷⁾.

Direct objective methods are generally specific; however, they are expensive and require infrastructure, are more associated with disease control, and do not always directly reflect the level of adherence, so they are not entirely practical and easy to apply. Indirect methods, on the other hand, show deviations, since patients frequently report non-compliance, fearing that this will affect the relationship with the physician. Therefore, the choice of the best measurement strategy to obtain an approximation of adherence behavior must meet basic psychometric standards of acceptable reliability and validity. In addition, they must be developed in such a way that patients answer them honestly, without bias and without fear of being judged for their behavior. There are different questionnaires that have been developed and validated for different diseases. Those most frequently identified in the literature are described below ⁽², ¹³, ²⁷, ²⁸, ²⁸, ²⁹, ³⁰, ³¹, ³², ³³, ³⁴⁾:

As a result of research and meetings in different countries, the WHO has recognized that interventions to eliminate barriers to therapeutic adherence must become a central component of efforts to improve population health worldwide ⁽²³, ³², ³⁰⁾. Indeed, even considering that there will initially be a possible increase in spending on drugs and education strategies, the impact of chronic disease control will significantly decrease the overall health budget, due to the reduced need for other more costly interventions (⁴², 55). This assertion has been substantiated by multiple studies that consistently demonstrate cost savings and significant increases in the effectiveness of health interventions that are attributable to low-cost interventions to improve adherence. Therefore, efforts should focus on increasing the effectiveness of adherence interventions, and this will have a much greater impact on population health than any improvement in specific medical treatments (56, 57, 58, ²⁰).

Speaking at the level of health systems, the WHO ⁽⁴⁶⁾ refers to five interacting dimensions that influence therapeutic adherence: 1) those related to the health care system or team; 2) socioeconomic; 3) those related to treatment; 4) those related to the patient; and 5) those related to the disease. If interventions aimed at positively impacting these factors are implemented, adherence will improve.

This review identified that, given that therapeutic adherence is a complex process and some of the strategies require considerable investments, two dimensions are those that, if addressed, will give effective results in the short and medium term for disease control: a) those related to the patient, and b) those related to the health care system or team ⁽²³, ³², ³⁸⁾.

Patient-related: for patients to cope effectively with the treatment related demands imposed by their disease, they must be informed, motivated and trained in the use of cognitive and behavioral self regulatory strategies. Effective delivery of care for chronic processes requires mobilizing the patient and the supporting community, but it is important to recognize that, for health systems, this is one of the most difficult elements to provide in the long term ⁽²³, ³², ⁴¹⁾. Health education in patients is a crucial element, since it has been shown that it can modify health care habits and generate confidence in medical treatment, especially in those sectors in which schooling is low, since this is associated with low therapeutic adherence (59).

In addition to the above, health education programs should be comprehensive and not only elaborated with clinical academic elements, since barriers to behavioral change should be addressed at the beginning of treatment with a focus on lifestyle change, and not only as general recommendations, but with strategies and activities achievable by patients and that take into account their culture and beliefs ⁽³¹, ³⁴⁾. Additionally, it is considered crucial to develop programs that involve the family, because family support can be an important facilitator of adherence to self-care. Indeed, it has been found that higher levels of family support can also improve the ability to overcome barriers to healthy behavior ⁽⁴⁵⁾.