Which medication is NOT a thiazide diuretic?

Spironolactone is indeed the medication that is not a thiazide diuretic. It is classified as a potassium-sparing diuretic, which means it works differently than thiazide diuretics. While thiazide diuretics, like hydrochlorothiazide, metolazone, and chlorthalidone, primarily act on the distal convoluted tubule of the nephron to inhibit sodium and chloride reabsorption, spironolactone acts on the collecting ducts and distal tubules. It antagonizes the action of aldosterone, promoting the retention of potassium while encouraging sodium and water excretion. This mechanism makes spironolactone particularly useful in conditions such as heart failure and hypertension but distinctly separates it from the thiazide class of diuretics.