Lack of adherence to prescribed antihypertensive regimens constitutes a barrier to adequate blood pressure control and prevention of cardiovascular events. Various means of measuring adherence to antihypertensive medications are currently available for use in clinical practice. The choice of the specific measure used in clinical practice depends on the intended use of the information, the resources available to the provider, as well as patient acceptance and convenience of the method. This article presents an overview of the advantages and limitations of the methods used to measure medication adherence that are currently available for use in outpatient settings, it also outlines provider strategies for addressing adherence issues related to antihypertensive medications. Indirect methods used to measure adherence in the outpatient setting include self report, electronic adherence monitoring (e.g. medication event monitoring system), pharmacy refill rates, and pill counts. Direct methods include the use of bioassays or biomarkers, which involve laboratory detection of the drug or a metabolic product of the drug in a biologic fluid, or laboratory detection of a biologic marker. Direct observation of the patient taking the medication is also another direct method; however, it is impractical in the outpatient setting, especially for long-term treatment. Each of these methods has advantages and disadvantages; perhaps using a combination of methods may provide the most accurate assessment of adherence. The information gained from measurement of adherence can help to formulate recommendations for individual patients regarding necessary adjustments to their medication-taking behavior to achieve the optimum outcome. Part of the difficulty associated with achieving better medication adherence lies in the inherent complexity of medication-taking decisions and behavior and of relationships between patients, their healthcare providers, and often others involved in the patient's care, such as family members. Poor medication adherence and ultimately, adverse cardiovascular outcomes, is related to a variety of factors: quality of life; complexity of medication regimens; costs of medications; adverse effects of medications; demographic, behavioral, treatment and clinical variables; knowledge of hypertension and healthcare system issues; and use of non-conventional therapies. To be effective, strategies employed in clinical practice to overcome nonadherence need to take into account patients' individual characteristics. Frequently, more than one strategy is necessary to bring about the desired level of adherence. The benefits of proven medical treatments are only available to patients who actively use them; thus, patient adherence to healthcare provider recommendations is the key mediator between medical practice and health outcomes.
