What is the primary effect of alpha blockers?

Alpha blockers primarily cause vasodilation and decreased blood pressure by blocking alpha-adrenergic receptors. These receptors, when activated by catecholamines like norepinephrine, typically lead to vasoconstriction and increased blood pressure. By inhibiting these receptors, alpha blockers prevent the usual constricting effect on vascular smooth muscle, leading to relaxation of the vessel walls. This results in a decrease in peripheral vascular resistance and, consequently, a reduction in blood pressure.

The primary therapeutic uses for alpha blockers include treating hypertension and conditions such as benign prostatic hyperplasia, where they help improve urine flow by relaxing smooth muscle in the prostate and bladder neck. Therefore, the ability of alpha blockers to induce vasodilation directly contributes to their effectiveness in lowering blood pressure, making this option the correct choice.