What is the primary effect of diuretics?

• A. Lower blood pressure by increasing urine
• B. Dilate blood vessels
• C. Constrict blood vessels
• D. Increase heart rate

Answer: (A)

The main idea is that diuretics lower blood pressure mainly by increasing urine output, which reduces blood volume. They act on the kidneys to promote excretion of sodium and water, so less fluid remains in the circulation. With reduced circulating volume, venous return to the heart drops, leading to lower preload and, consequently, lower cardiac output and blood pressure. Over time there can be a small drop in systemic vascular resistance as well, but the immediate and primary effect is volume loss from diuresis. They do not directly dilate or constrict blood vessels, and increasing heart rate is not the primary goal (any rate change is a secondary reflex).