What is patient adherence? A terminology overview.

It is well known that patient adherence to appropriately prescribed medications is essential for treatment efficacy and positive therapeutic outcomes. It is also understood that patients who are prescribed medications do not necessarily take them as prescribed. Indeed, variation in patients' medication-taking is an age old conundrum which remains the focus of much interest amongst researchers and clinicians owing to its far-reaching consequences. Despite the extensive adherence-related research over the last four decades and a recent surge in this field, there remains a lack of uniformity in the terminology used to describe adherence and its related concepts. In turn, it is often difficult to conduct comparisons between adherence-related studies, which may be associated with the non-cumulative nature of work in this field. The purpose of this commentary is to provide an overview of key terminology relating to the field of adherence research.