The researchers note that a recent meta-analysis of 6 studies and 814 study participants indicated that the odds of good blood pressure control among patients adherent to antihypertensive medications was 3.44 compared to those who were nonadherent.

According to the researchers, "asymptomatic characteristic and lifelong nature of hypertension are two key factors that undoubtedly contribute to poor patient adherence to drug regimens."

Factors that influence adherence include patient demographics, side effects of medication, convenience of drug dosing, cost and number of medications, patients' knowledge, beliefs and attitudes about hypertension and its treatment, patients' involvement with their care, and health care system issues.

Demographic factors associated with higher compliance in patients with hypertension include white race, being a newly diagnosed female and being older. In addition, daily dosing regimens for antihypertensive medications and those that improve quality of life are associated with higher adherence whereas depression has recently been linked to reduced adherence.

"Improving the efficiency of key health care system functions, such as financing and proper pharmaceutical management as well as delivery of care, can make a substantial contribution to improving medication adherence rates in hypertensive patients," Dr. Krousel-Wood and colleagues note.

"Several of the factors that have an adverse impact on adherence to prescribed therapy in hypertensive patients may lead to increased patient use of nonconventional therapy, which may also contribute to low adherence to prescribed therapies," they suggest.