What Are Diuretics?

Diuretics are a common medication used to treat high blood pressure. They are relatively inexpensive and are widely available. In addition to high blood pressure, diuretics are often used to treat other illnesses, including:

  * Heart Failure
  * Edema
  * Some types of poisoning

While the general action of diuretics is to increase excretion of salt and water, many diuretics can lower blood pressure at lower doses than those needed to cause diuresis (excretion).

Diuretic Types and Brands. The many brands of diuretics are generally inexpensive. Some need to be taken once a day, some twice a day. Low doses are usually as effective for lowering blood pressure as higher doses. Diuretics are usually used in combination with other drugs, especially ACE inhibitors and beta blockers.

The three main types of diuretics include:

  * Thiazide diuretics. These include chlorothiazide (Diuril), chlorthalidone (Hygroton), indapamide (Lozol), hydrochlorothiazide (Esidrix, HydroDiuril), bendroflumethiazide (Naturen), methylclothiazide, (Edduran), and metolazone (Mykrox, Zaroxolyn). In most cases, thiazides are preferred to other diruetics for treatment of high blood pressure.
  * Potassium-sparing diuretics. These include amiloride (Midamor), spironolactone (Aldactone), and triamterene (Dyrenium).
  * Loop diuretics. Because loop diuretics act faster than other diuretics it is important to avoid dehydration and potassium loss. Loop diuretics include bumetanide (Bumex), furosemide (Lasix), ethacrynic acid (Edecrin), and torsemide (Demadex).

Problems with Diuretics.

  * Loop and thiazide diuretics reduce the body’s supply of potassium, which, if left untreated, increases the risk for arrhythmias. Arrhythmias are heart rhythm disturbances that can, rarely, lead to cardiac arrest. In these cases, doctors will prescribe lower doses of the current diuretic, recommend potassium supplements, or use potassium-sparing diuretics either alone or in combination with a thiazide.
  * Potassium-sparing drugs have their own risks, which include dangerously high levels of potassium in people with existing elevated levels of potassium or in those with damaged kidneys. However, all diuretics are generally more beneficial than harmful.
  * Thiazide diuretics may increase blood sugar levels.
  * Erectile dysfunction (impotence) may be a side effect of thiazides.
  * Elevated uric acid levels, and possibly gout, may be caused by thiazide diuretics.

Common Diuretic Side Effect Symptoms.

  * Fatigue
  * Depression and irritability
  * Urinary incontinence
  * Reduced sexual drive and problems with obtaining and maintaining an erection

What Is a Thiazide Diuretic
Various types of a thiazide diuretic are mostly used for patients with high blood pressure and surely they work well. The drugs that belong to this type of diuretics are xipamide, indapamide, metolazone, cyclopenthiazide, chlorthalidone and bendroflumethiazide. If you are taking thiazide diuretics it is important to note that you should take them constantly. If the medication works and you feel fine, it doesn’t mean that you should stop taking the medication.

Thiazide diuretics have been a mainstay of the therapy of essential hypertension.  The most popular agent in this class, hydrochlorothiazide, was traditionally used in doses of 50 to 100 mg per day. These doses were associated with metabolic and electrolyte complications. Low dose therapy has since been demonstrated to be efficacious and to have a much lower incidence of side effects. Diuretics increase the amount of water that is passed through urine. When using the thiazide diuretics you should know that there are side effects that come with the medication. This drug can increase the amount of sugar in the patient’s blood, so in a case of diabetes it is important to check with a doctor so that specific prescriptions on maintaining your blood sugar level would be given.

Thiazide diuretics can also increase the level of uric acid and cause gout attacks so this should be noted. Pottassium, sodium, and magnesium are important for the body, that’s why you should be aware of the fact that thiazides can sometimes change the salt balance in the body and cause decreasing of the amounts of the above mentioned elements. Additional side effects of this medication are dizziness and stomach upset.

What are thiazide diuretics and what are they used for?

A diuretic is a medicine which increases the amount of water that you pass out from your kidneys. (A diuretic causes a ‘diuresis’ - an increase in urine.) So, they are sometimes called ‘water tablets’. There are different types of diuretics which work in different ways.

Thiazide diuretics are one type of diuretic. The most commonly used thiazide is called bendroflumethiazide (bendrofluazide). Other thiazide diuretics include chlortalidone (chlorthalidone), benzthiazide, clopamide, cyclopenthiazide, hydrochlorothiazide, xipamide, indapamide, hydroflumethiazide and metolazone. Each comes in different brand names.

Thiazide diuretics are a common treatment for high blood pressure. They are also used to clear fluid from the body in conditions where your body accumulates too much fluid such as heart failure. (But, a type of diuretic called a ‘loop diuretic’ is more commonly used to treat heart failure.)

Thiazide Diuretics Interactions:

Potassium —Probable Need for Supplementation | Magnesium —Supplementation Possibly Helpful | Calcium —Possible Dangerous Interaction | Coenzyme Q 10 (CoQ 10) —Supplementation Possibly Helpful | Zinc —Supplementation Possibly Helpful | Licorice —Possible Dangerous Interaction

Drugs in this family include:

  * Bendroflumethiazide (Naturetin)
  * Benzthiazide (Exna)
  * Chlorothiazide (Diurigen, Diuril)
  * Chlorthalidone (Hygroton, Thalitone)
  * Hydrochlorothiazide (Esidrix, Ezide, HydroDIURIL, Hydro-Par, Microzide, Oretic)
  * Hydroflumethiazide (Diucardin, Saluron)
  * Indapamide (Lozol)
  * Methyclothiazide (Aquatensen, Enduron)
  * Metolazone (Mykrox,  Zaroxolyn)
  * Polythiazide (Renese)
  * Quinethazone (Hydromox)
  * Trichlormethiazide (Diurese, Metahydrin, Naqua)
  * and others

What are the possible side-effects of thiazide diuretics?

Side-effects are uncommon as the dose needed to lower blood pressure is low. The leaflet which comes in the tablet package provides a full list of possible side-effects. These include:

  • A possible increase in your blood sugar level. Some people with diabetes may need more treatment to keep the blood sugar level normal.
  • A possible increase the level of uric acid. So, if you have gout you may have more gout attacks. A first attack of gout is sometimes triggered by taking a diuretic.
  • The salt balance in the bloodstream is sometimes upset which can cause a low blood level of potassium, sodium, and magnesium, and a high level of calcium level. These effects may cause weakness, confusion, and rarely, abnormal heart rhythms to develop. You may be advised to have a blood test to check for these problems.
  • Other problems such as: upset stomach, dizziness on standing (due to too low blood pressure), impotence (reversible on stopping treatment), and skin sensitivity to sunlight.


Hyponatremia is an important side effect of thiazide diuretics, and I think that it deserved further discussion in the recent review article by Ernst and Moser (Nov. 26 issue). Although thiazide-induced hyponatremia is not as well characterized as thiazide-induced hypokalemia, it probably occurs as frequently. The clinical outcomes of hyponatremia secondary to the use of thiazide diuretics vary from mild fatigue or nausea to severe neurologic compromise, including death.  Although difficult to predict, it usually occurs within 2 weeks after the initiation of treatment with thiazide diuretics, and risk factors for the development of hyponatremia include older age, female sex, and low body weight.  The pathogenesis is believed to be a combination of thiazide-induced factors such as renal sodium loss and antidiuretic hormone stimulation and patient factors such as age-related impairment of free-water excretion and increased water intake.  Management of symptomatic hyponatremia can be challenging and requires frequent monitoring of the serum sodium level to reduce the risk of osmotic demyelination.  If the hyponatremia is mild or asymptomatic, the patient should be counseled about the risks and benefits of the continued use of the thiazide diuretic, avoiding excessive free-water intake, and careful monitoring of the serum sodium level.

Tara Cowtan, M.D.
Townsville Hospital
Townsville, QLD, Australia
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  3. Sonnenblick M, Friedlander Y, Rosin AJ. Diuretic-induced severe hyponatremia: review and analysis of 129 reported patients. Chest 1993;103:601-606.
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  7. From Craig Weber, M.D., former About.com Guide

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