A Complete Guide to Diuretics

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Diuretics, also known as "water pills," increase the flow of urine. This helps get rid of extra salt and water from the body.

Diuretics can help various medical conditions caused by too much fluid. They can lower blood pressure by reducing the fluid in your blood that your heart has to pump. Diuretics can also be used to treat heart failure, brain swelling (edema), eye swelling, and swelling secondary to liver or kidney disease.

This article discusses the different types of diuretics and how they work.

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How Diuretics Work

Diuretics work by acting on the kidneys' nephrons. The nephron is the part of the kidney that is responsible for filtering fluids and waste that make up urine. Each of your kidneys has about a million nephrons.

The nephrons work as follows:

  • When blood enters the nephron, it flows into a cluster of tiny blood vessels, called the glomerulus.
  • The glomerulus filters your blood. It allows smaller molecules, waste, and fluid to enter the tubule. Protein and blood cells, which are larger molecules, stay in the blood vessel.
  • The tubule removes wastes and returns minerals to your blood. Fluid and waste in the tubule become urine.

Recap

Diuretics work by affecting the kidney's nephrons, which filter waste and fluid to make urine.

Types of Diuretics

There are several types of diuretics your doctor may prescribe. Each medication has a different way that it works to remove fluid or salt from the body. Your doctor will consider your specific condition, benefits, and risks when working with you to choose a diuretic.

Carbonic Anhydrase Inhibitors

Carbonic anhydrase inhibitors, like acetazolamide, are mainly used to lower fluid pressure in the eye to treat glaucoma.

The medicine works by limiting an enzyme called carbonic anhydrase. This is an enzyme in the tubule that puts minerals, sodium, and water back in your blood. The medication limits this enzyme, so it increases the amount of water that leaves your body through urine.

Sodium-Glucose Cotransporter 2 (SGLT2) Inhibitors

Sodium-glucose cotransporter 2 (SGLT2) inhibitors decrease the glucose and sodium going back into your blood. With fewer sodium ions reabsorbed in your blood, fluid levels decrease, which makes it act as a mild diuretic.

SGLT2 drugs like canagliflozin and dapagliflozin are technically mild diuretics. However, they're mostly used to treat diabetes, since they decrease glucose in your blood.

Recap

Carbonic anhydrase inhibitors increase the amount of water that leaves your body through urine. Sodium-glucose cotransporter inhibitors decrease glucose and sodium in your blood, which also makes fluids decrease.

Loop Diuretics

Loop diuretics affect a part of your kidneys called the loop of Henle. They remove salt and excess water from your body.

Loop diuretics may also cause you to lose too much potassium. If the potassium loss is severe enough, hypokalemia (low potassium levels) can result. In severe cases, hypokalemia can lead to abnormal heart rhythms and even cause it to stop.

Loop diuretics, such as furosemide, are used to treat hypertension (high blood pressure), fluid in the lungs (pulmonary edema), generalized swelling, and hyperkalemia (dangerously high potassium levels). As an off-label use, they may be prescribed for hypercalcemia or high calcium levels.

Recap

Loop diuretics remove extra fluid and salt. They're used to treat hypertension as well as other conditions such as fluid in the lungs and generalized swelling.

Thiazides

Thiazides prevent the reabsorption of sodium and water in part of the nephron called the distal convoluted tubule. This causes more water to leave the body as urine.

Like loop diuretics, thiazides can also cause the levels of potassium in your body to drop. Your doctor will monitor your potassium levels while you're taking the medicine.

Thiazides are used as a first-line (or first-recommended) treatment of high blood pressure (hypertension). In fact, a 2019 study found that thiazides are more effective as first-line treatment of hypertension than ACE inhibitors, another common treatment.

When glomerular filtration rate (a measure of kidney function) is very low, thiazides may not work as well. In some cases, thiazides may be combined with loop diuretics to increase their effects.

Thiazides are also used to treat calcium-containing kidney stones and diabetes insipidus.

Recap

Thiazides are commonly recommended to treat high blood pressure. They help to get rid of fluid through urine, but they can also cause potassium levels to drop.

Potassium-Sparing Diuretics

As their names suggest, potassium-sparing diuretics work by increasing urine volume without decreasing potassium. Potassium-sparing diuretics include spironolactone and amiloride.

Spironolactone prevents the action of aldosterone, a steroid hormone produced by the adrenal gland. It causes the kidneys to get rid of extra water and sodium while reducing the loss of potassium.

Spironolactone is often used to counteract potassium loss caused by thiazide and loop diuretics. It may also be used to treat hyperaldosteronism, a condition where the body produces too much aldosterone.

Amiloride blocks the reabsorption of water into your body. Like spironolactone, amiloride is often used to counteract potassium loss caused by other diuretics.

Recap

Potassium-sparing diuretics include spironolactone and amiloride. They get rid of extra water and sodium and reduce potassium loss.

Osmotic Diuretics

Osmotic diuretics draw in water through osmosis. Osmosis is the passing of water from a less concentrated solution to a more concentrated solution.

Osmotic diuretics prevent water from being reabsorbed and allow it to exit the body. They work in the kidneys as well as around the brain and eye to draw off water and reduce swelling. This can treat glaucoma as well as increased intracranial pressure.

Osmotic diuretics are also used to prevent acute kidney (renal) failure after chemotherapy or rhabdomyolysis (muscle breakdown).

Vaptans

Vasopressin receptor antagonists or vaptans (conivaptan and tolvaptan) are used to treat conditions like low sodium in people with heart failure. They work by increasing the amount of water that's released as urine. This increases the level of sodium in the blood.

Recap

Osmotic diuretics draw in water and keep it from being reabsorbed so it can exit the body. Vaptans increase the amount of water in urine, which increases the body's sodium levels.

Summary

Diuretics treat medical conditions caused by too much fluid. They help remove extra salt and fluid from the body by increasing urine. Different types of diuretics are available to treat specific conditions, including high blood pressure, glaucoma, and fluid in the lungs.

A Word From Verywell

If you have high blood pressure or another condition that could benefit from diuretics, talk to your healthcare provider.

Most diuretics are available by prescription, but some can be purchased without a prescription. In some cases, they can cause side effects, including dehydration, and make some conditions worse. It's best to discuss your health history with your health care provider before taking diuretics.

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8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
  • Eaton DC, Pooler JP. Chapter 8. Regulation of Potassium Balance. In: Eaton DC, Pooler JP. eds. Vander's Renal Physiology, 8e. New York, NY: McGraw-Hill.

  • Sam R, Pearce D, Ives HE. Diuretic Agents. In: Katzung BG, Trevor AJ. eds. Basic & Clinical Pharmacology, 13e. New York, NY: McGraw-Hill.