Various antihypertensive drugs reduce blood pressure by different mechanisms. In some instances, adverse reactions occur because of specific hemodynamic effects. Examples include syncope with alpha-blockade or vasodilator therapy; fatigue or exercise intolerance with the reduction in cardiac output following the use of beta-adrenergic inhibitors; edema, headaches, or dizziness with the use of vasodilators such as calcium entry blockers; renal failure in patients with renal artery stenosis or renal insufficiency following the use of ACE inhibitors; and marked hyponatremia with volume depletion following the use of diuretics, especially in elderly patients. In the majority of patients, however, blood pressure lowering can be achieved without significant adverse effects. Combining small doses of different agents with different hemodynamic actions often results in good blood pressure control and minimal reactions. Examples of these include diuretics and beta-adrenergic inhibitors, diuretics and ACE inhibitors, and beta-blockers and vasodilators.