Compliance with medical therapy represents a multifactorial problem with marked consequences for individual and public health. Among the many contributing factors, the choice of drug may also determine the degree of compliance. Various studies investigating either compliance or persistence with antihypertensive therapy using a variety of methods have suggested that adherence to therapy may show the following pattern: diuretics < beta-blockers < calcium channel blockers < ACE inhibitors. Furthermore, two recent studies have shown that therapy with angiotensin II receptor blockers may be associated with better long-term adherence than other antihypertensive monotherapies including angiotensin converting enzyme inhibitors. Since medication compliance with antihypertensive therapy, among other factors, closely correlates with the experience of side effects, it may be speculated that the different classes of antihypertensives may induce varying degrees of compliance and persistence due to their different tolerability profiles. Side effects may induce variable compliance and nonpersistence by yet another mechanism. Therapy turbulence, ie, any change in medication, is also associated with nonpersistence. Therefore, side effects may directly or indirectly (via inducing therapy turbulence) underly variable compliance and nonpersistence.