Towards a clarification of terminology in medicine taking behavior: compliance, adherence and concordance are related although different terms with different uses.

Medical terminology is at continuous process of change since the language of medicine needs the rapid incorporation of new terms or changing the existing ones to be in touch with new ideas, concepts and practices. The evolution of the terms "compliance", "adherence" and "concordance" in the field of medicine-taking represents a good example of this. Although these three terms are frequently used interchangeably generating some confusion, compliance, adherence and concordance mean different things and must be used in different ways. Compliance refers to the extent to which patients follow doctors' prescription about medicine taking; adherence refers to the extent to which patients follow through decisions about medicine taking; and concordance refers to the extent to which patients are successfully supported both in decision making partnerships about medicines and in their medicines taking. This terminology evolution may actually be more important than mere semantics since better adherence to a treatment regimen could be achieved through open-ended physician-patient communication, incorporating the beliefs and preferences of the patient in the decision-making process. At present time, concordance could be useful as a normative or aspirational term while compliance and adherence must be the terms used for scientific measurement in medicine-taking field.