**1. Introduction**

Chronic diseases such as diabetes, stroke, arthritis, and heart diseases are the main cause of disability and death throughout the world. More than 40% of the people suffer in their adult

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life from a chronic disease, and approximately 20% are hospitalized because of it. Another perspective is that they are costly, but in many cases preventable. The main cause is usually lifestyle choices that are hard to change; eating foods that are low in fats, becoming more physically active, and avoiding tobacco can help from developing high-risk conditions and diseases.

Patients with multiple chronic diseases struggle with great challenges on their daily lives; also, they experience poor health outcomes and will tend to use health national services more than patients with single chronic disease. Not respecting treatment prescriptions have both personal health impact and health economics consequences. These people are regarded as the highest cost patient populations in the healthcare system [1], with a poor adherence to treatment and medical advices. Worldwide, experts are examining the situation in which health care can be better organized to meet the needs of every patient. It was demonstrated that every dollar spent for improving adherence saves seven dollars in total healthcare costs [2, 3].

The absence of appropriate clinical practice guidelines for patients with multiple chronic diseases is a huge problem, which healthcare providers contend. Furthermore, patientcentered care needs to be supported through the transition of a more oriented approach to help patients prioritize their condition.

Moreover, not taking the required medication prescribed can have both personal health impact and health economics consequences. Recently, patients have shown increased interest in their own healthcare possibilities, raising the overall rate of adherence to treatment. However, the cost-effectiveness is still a parameter that is often ignored when a medical expert chooses to treat different kinds of conditions. Adherence is defined as "persistence in a practice," so this definition emphasizes the routine that people with chronic disease ideally engage in when taking prescription medication [4].

The term first used was "compliance." Charavel et al. [5] described this concept like physician alone makes the treatment decision, while the passive and dependent patient is obliged to comply with it. But the patient is not so silent and the term "adherence" is more used, the patient is more engaged in taking prescription medication.

Adherence cannot be defined as an "all or nothing" response in which the patient either follows the prescriber's instruction to the letter (adherence) or deviates from it in some way (nonadherence) [6]. A patient is considered adherent if he/she takes 80% of his/her prescribed medicine(s). In the current era of free and easy access to information, with a higher educational level across the population, the concept of "concordance" seems to win for some diseases, when the patient want to defer decisions entirely to their health professionals or family members. Some patients prefer a collaborative role, whereas others prefer a passive role.

The most common chronic diseases that have a low adherence rate to treatment are asthma, diabetes, heart disease, obesity, rheumatic diseases, eating disorders, chronic obstructive pulmonary disease (COPD), and psychotic disorders.

The estimated rate of adherence is only half of the percentage of the patients with chronic diseases. Ten days after a new prescription has been filled [7], another quarter of the patients have missed one dose of the medication (intentionally or unintentionally). This kind of behavior causes concern among the medical experts, so they have to make strong decisions in order to make the treatment more functional for every patient.

The top three therapy classes used for chronic diseases are inflammatory conditions, multiple sclerosis, and cancer. These three account more than a half of the total spend for all specialty medications. The new trend is that patients often shift from using brand medications to lower cost generics; as they do this, the copayments decline and also the adherence drops significantly.

The medications used to treat diabetes, high blood cholesterol and high blood pressure, ulcer, and asthma were the most expensive traditional therapy class. Also these classes had the minimum nonadherence rate (between 20 and 35%). In the case of ulcer disease, it is more likely for aged people to be more adherent to the treatment. Asthma is another case of strong nonadherence cases for the pediatric patients.

Correct understanding of barriers for adherence and strategies used can help physicians educate their patients more appropriately, reducing the risk of nonadherence and achieving an improvement of the healthcare system [8].

A lot of studies were done to estimate the costs related to nonadherence to drug therapy in developed countries, making distinctions between primary nonadherence (prescriptions not being filled by the patient) and secondary nonadherence (medication not being taken as prescribed). World Health Organization (WHO) published in 2003 a report of poor adherence to treatment of chronic diseases in which developing countries were found to have a higher rate of nonadherence than the 50% average of nonadherence to long-term therapy for chronic diseases in developed countries [9].

Mills et al. [10] examined both developed and developing nations in a systematic review of adherence and reported the same important barriers (fear of disclosure, substance abuse, forgetfulness, suspicions of treatment, too complicated regimens, too many pills, and decreased quality of life), with some facilitators reported by patients in developed nation (having a sense of self-worth, accepting their disease, understanding the need for strict adherence, making use of reminder tools, and having a simple regimen).
