It is well known that high blood pressure increases the risk of ischaemic heart disease 3- to 4-fold (27) and of overall cardiovascular risk by 2- to 3-fold (11). The incidence of stroke increases approximately 3-fold in patients with borderline hypertension and approximately 8-fold in those with definite hypertension (12). It has been estimated that 40% of cases of acute myocardial infarction or stroke are attributable to hypertension (13-15).

Despite the availability of effective treatments, studies have shown that in many countries less than 25% of patients treated for hypertension achieve optimum blood pressure (16). For example, in the United Kingdom and the United States, only 7% and 30% of patients, respectively, had good control of blood pressure (17) and in Venezuela only 4.5% of the treated patients had good blood pressure control (18). Poor adherence has been identified as the main cause of failure to control hypertension (19 - 25). In one study, patients who did not adhere to beta-blocker therapy were 4.5 times more likely to have complications from coronary heart disease than those who did (26). The best available estimate is that poor adherence to therapy contributes to lack of good blood pressure control in more than two-thirds of people living with hypertension (20).

Considering that in many countries poorly controlled blood pressure represents an important economic burden (e.g. in the United States the cost of health care related to hypertension and its complications was 12.6% of total expenditure on health care in 1998) (28), improving adherence could represent for them an important potential source of health and economic improvement, from the societal (29), institutional (30) and employers' point of view (31,32).