Randomized trials in the study of antihypertensive drugs. Heterogeneity in response to antihypertensive drugs can be addressed by randomized trials in individual subjects. In such a trial a patient receives pairs of treatment periods (one period of each pair active drug, one matched placebo, in random order); patient and clinician are blinded to allocation, and treatment targets are monitored. These trials can optimize antihypertensive therapy in clinical practice and facilitate the investigation of new drugs and the study of pathophysiology. Such trials also have potential in helping decide whether common, nonspecific symptoms reported by patients are really drug related. 