Thiazide diuretics (water pills) are medications that are used to treat high blood pressure (hypertension) and reduce fluid accumulation in the body. They work by reducing the ability of the kidneys to reabsorb salt and water from the urine and into the body thereby increasing the production and output of urine (diuresis).

• chlorthalidone (Thalitone)
• hydrochlorothiazide (Microzide)
• methyclothiazide

Thiazide diuretics are used to treat high blood pressure and congestive heart failure as well as the accumulation of fluid and swelling (edema) of the body caused by conditions such as heart failure, cirrhosis, chronic kidney failure, corticosteroid medications, and nephrotic syndrome.

Side effects of thiazide diuretics are dose related and include:

• dizziness and lightheadedness,
• blurred vision,
• loss of appetite,
• itching,
• stomach upset,
• headache, and
• weakness.

Other side effects and adverse reactions are:

• An increased sensitivity to sunlight (prolonged sun exposure should be avoided)
• Owing to their ability to increase the production of urine, these drugs may lower levels in the body of potassium and magnesium which also are present in urine.
• Thiazide diuretics may increase uric acid levels in blood.
• Like other antihypertensive medications, thiazides cause sexual dysfunction.

Thiazide diuretics are similar in effectiveness and usually are not effective in people with severe renal impairment.

Thiazide diuretics can lower potassium and magnesium blood levels since they are both eliminated in urine. Low levels of potassium and magnesium in the blood can result in abnormal heart rhythms, particularly in those who are also taking digoxin (Lanoxin) in addition to a thiazide. Thiazide diuretics can increase the risk of lithium (Eskalith, Lithobid) toxicity by reducing the kidney's ability to eliminate lithium in the urine.

Drugs known as nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Motrin), naproxen (Naprosyn), and nabumetone (Relafen) can reduce the effectiveness of thiazide diuretics in lowering blood pressure because they may reduce the ability of the kidneys to make urine, particularly in patients who have reduced kidney function.

People who have diabetes may have increased blood sugar levels when taking thiazide diuretics.

It is not recommended to use thiazide diuretics with dofetilide (Tikosyn), a drug used for treating abnormal heart rhythms, as this may increase the blood levels of dofetilide (Tikosyn) and cause abnormal heart rhythms. Thiazide diuretics can reduce how the body responds to norepinephrine and render norepinephrine less effective.