Adherence (compliance) and concordance

In medicine, compliance (also adherence, capacitance) describes the degree to which a patient correctly follows medical advice. Most commonly, it refers to medication or drug compliance, but it can also apply to other situations such as medical device use, self care, self-directed exercises, or therapy sessions. Both the patient and the health-care provider affect compliance, and a positive physician-patient relationship is the most important factor in improving compliance, although the high cost of prescription medication also plays a major role.

Compliance is commonly confused with concordance, which is the process by which a patient and clinician make decisions together about treatment.

Worldwide, non-compliance is a major obstacle to the effective delivery of health care. Estimates from the World Health Organization (2003) indicate that only about 50% of patients with chronic diseases living in developed countries follow treatment recommendations. In particular, low rates of adherence to therapies for asthma, diabetes, and hypertension are thought to contribute substantially to the human and economic burden of those conditions. Compliance rates may be overestimated in the medical literature, as compliance is often high in the setting of a formal clinical trial but drops off in a "real-world" setting.

Major barriers to compliance are thought to include the complexity of modern medication regimens, poor "health literacy" and lack of comprehension of treatment benefits, the occurrence of undiscussed side effects and poor treatment satisfaction, the cost of prescription medicine, and poor communication or lack of trust between the patient and his or her health-care provider. Efforts to improve compliance have been aimed at simplifying medication packaging, providing effective medication reminders, improving patient education, and limiting the number of medications prescribed simultaneously. Current studies show a great variation in terms of characteristics and effects of interventions to improve medicine adherence. It is still unclear how adherence can consistently be improved in order to promote clinically important effects.

An estimated half of those for whom treatment regimens are prescribed do not follow them as directed. Until recently, this was termed "non-compliance", which was sometimes regarded as meaning that not following the directions for treatment was due to irrational behavior or willful ignoring of instructions. Today, health care professionals more commonly use the term "adherence" to a regimen rather than "compliance", because this term is thought to reflect better the diverse reasons for patients not following treatment directions in part or in full. Additionally, the term adherence includes the ability of the patient to take medications as prescribed by their physician with regards to the correct drug, dose, route, timing, and frequency. It is noted that compliance may only refer to passively following orders. However, the preferred terminology remains a matter of debate. In some cases, concordance is used to refer specifically to patient adherence to a treatment regimen that is designed collaboratively by the patient with the physician, to differentiate it from adherence to a physician-only prescribed treatment regimen. Despite the ongoing debate, adherence is the preferred term for the World Health Organization, The American Pharmacists Association, and the U.S. National Institutes of Health Adherence Research Network.

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