Despite the potential of modern pharmacotherapy to control disease and enhance quality of life, two out of five patients fail to take their prescribed medication correctly. Research indicates that the two primary influencers of adherence are the patient's beliefs in the value of the regimen and the patient's ability to overcome practical barriers to adherence. The patient's perception of value--ie, the risks, benefits, and efficacy of therapy--influences his or her commitment to the medication regimen. Barriers to adherence include side effects, number and frequency of dosages, and cost. Communication between health care providers and patients is crucial to enhancing patient adherence to medication regimens.