Effect of perceived barriers on compliance with antihypertensive medication.

Noncompliance with antihypertensive medication remains an obstacle to the management of hypertension, and despite research efforts over the past decade, the predictors of noncompliance remain unclear. According to values expectancy theory, individuals rationally choose noncompliance when the barriers or costs of treatment outweigh the expected benefits. Noncompliance, therefore, is likely to occur when net costs of treatment are high. Using a cross-sectional study design among subjects (n = 197) attending a specialized clinic for hypertension, we measured "net barriers" (costs), self-reported compliance, and possible determinants of noncompliance, including socio-demographics, the medical regimen, and locus of control. The effect of each quartile of the net barriers score (none, low, moderate, and high) on compliance, controlling for potential effect modifiers, was assessed using logistic regression modeling. Noncompliance (47%) was associated with younger age, higher salt use, longer duration of treatment, and higher levels of net barriers, but duration of treatment modified the effect of net barriers. Among subjects in short-term treatment, noncompliance increased with severity of net barriers suggesting a dose-response effect. In contrast, patients in long-term treatment showed no dose-response effect but a consistent association between noncompliance and levels of net barriers. Subjects at greater risk for noncompliance, however, were those who reported high net barriers, regardless of duration of treatment. Net barriers accounted for 50% of the noncompliance and appeared most important for patients who were younger or in the early stages of treatment. Implications for health care providers are discussed.