Clinical trials have demonstrated that the treatment of mild-to-moderate hypertension can reduce the risk of stroke by 30 to 43% (1 - 4) and of myocardial infarction by 15% (5). Other costly consequences of untreated hypertension can also be prevented or minimized by effective treatment. Examples of the benefits of treatment include reduction in risk of cardiac failure, reduction in incidence of dementia (6), preservation of renal function and prevention of blindness in diabetic patients with hypertension (7 - 9).

Traditionally, the term compliance has been employed to mean the extent to which the patient, when taking a drug, complies with the clinician's advice and follows the regimen (10). However, the new era of patient-oriented care has led to the use of this term being questioned, and alternative terms such as adherence, persistence and concordance have been suggested (11 - 14).

In addition to the confusing terminology in the area of adherence, there has been controversy over the use of 80% as a cut-off point to distinguish adherence from nonadherence. In most studies, nonadherence has been considered to occur when patients do not take ≥ 80% of their prescribed antihypertensive drugs (15,16).

Whatever the definition, poor adherence to treatment is the most important cause of uncontrolled blood pressure (13,14,17) and only 20 to 80% of patients receiving treatment for hypertension in real-life situations are considered to be "good compliers" (18).