Adherence to therapy and adverse drug reactions: is there a link?

INTRODUCTION: Advances in biomedical technology and access to effective medications have resulted in significant improvements in patient survival and quality of life. Patient adherence is crucial to quality healthcare outcomes; however, achievement of consistent adherence remains difficult. Patient non-adherence represents an important health problem, from a clinical/economic viewpoint, being associated with reduced treatment benefits and significant financial burden. Non-adherence potentially leads to adverse drug events (ADEs), which are generally responsible for poorer health outcomes and avoidable resource misuse. Further, adverse drug reactions (ADRs) exemplify one of the most significant barriers to patients' medication-taking behavior with further detrimental clinical/economic outcomes. AREAS COVERED: The authors review adherence definitions and its measurement, emphasizing the consequences of the New European Pharmacovigilance Legislation on ADR definition. They analyzed the causes and the clinical/economic consequences of non-adherence and ADEs/ADRs in order to highlight a possible causal link. EXPERT OPINION: Careful assessment of this harmful relationship is crucial in planning for the interventions needed to improve effectiveness of pharmacological care and to safeguard the sustainability of healthcare systems. Finally, through the 'deactivation' of this link, there will be more chance that advances in healthcare technologies will realize their potential to reduce the burden of chronic illness.