Medication is an essential tool in the clinician's armamentarium yet it is estimated that 50% of patients
with a chronic health condition fail to adhere to prescribed treatments. This chapter outlines
what we mean by adherence and the implications of nonadherence in chronic health conditions.
Difficulties in measuring adherence are discussed, followed by a brief review of theoretical models
used to explain nonadherence. The chapter concludes with a discussion of the major practical
issues that affect patient adherence and strategies for clinical intervention.