Thiazides are a class of drug that promote water loss from the body ((diuretics)). They inhibit Na⁺/Cl^- reabsorption from the distal convoluted tubules in the kidneys. Thiazides also cause loss of potassium and an increase in serum uric acid.

Thiazides are often used to treat hypertension, although the mechanism is not fully understood. They may cause vasodilation by inhibiting calcium release induced by norepinephrine.