Hydrochlorothiazide in pregnancy, thiazide diuretics may cause an increased risk of congenital defects. Hydrochlorothiazide belongs to the thiazide class of diuretics, acting on the kidney to reduce sodium reabsorption in the distal convoluted tubule. Some of the side effects that may occur while taking Microzide include black, tarry stools blood in urine or stools cough or hoarseness fever or chills joint pain lower back or side pain painful or difficult urination. Hydrochlorothiazide has an additive effect on lowering blood pressure. You are or will be breast-feeding while you use Hydrochlorothiazide, check with your doctor. If you are or will be breast-feeding while you use Hydrochlorothiazide. Hydrochlorothiazide may increase the blood level of the medicine lithium, and this medicine is therefore not recommended for people taking lithium. The kidney's ability to retain water. Hydrochlorothiazide may increase the blood level of the medicine lithium, and this medicine is therefore not recommended for people taking lithium.