Which of the following is NOT a diuretic?

• A. Furosemide
• B. Spironolactone
• C. Hydrochlorothiazide
• D. Metformin

Answer: (D)

The key idea here is to recognize which medications actually promote urine production by acting on the kidneys. Diuretics work by blocking specific reabsorption steps in the nephron to increase urine output. Furosemide is a loop diuretic that blocks the Na-K-2Cl transporter in the thick ascending limb, producing a strong diuretic effect. Spironolactone is a potassium-sparing diuretic that antagonizes aldosterone in the collecting ducts, reducing sodium reabsorption and water retention. Hydrochlorothiazide is a thiazide diuretic that inhibits NaCl reabsorption in the distal convoluted tubule, also increasing urine output.

Metformin does not affect renal salt or water handling. It is an oral antidiabetic medication that lowers hepatic glucose production and improves insulin sensitivity; it has no diuretic action. So the medication that is not a diuretic is Metformin.