What Are Diuretics?

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 lower blood pressure by reducing the fluid in your blood that your heart has to pump.

This article discusses what diuretics treat and how they work. It also covers the types of diuretics, side effects, risks, and complications.

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What Do Diuretics Treat?

Healthcare providers may prescribe diuretics to decrease fluid levels when treating various conditions. These include:

Types of Diuretics

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

Some diuretics can be purchased over-the-counter, but their effects are typically more mild than prescription. Many over-the-counter diuretics are herbal remedies, like dandelion root. Herbal supplements aren't regulated like medications and may cause drug interactions. Always check with a healthcare provider before taking a supplement.

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.

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.

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.

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. This is a condition where the body produces too much aldosterone, a hormone that controls your balance of water and salt.

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

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.

Side Effects of Diuretics

Diuretics can cause side effects that include:

  • Frequent urination
  • Muscle cramps
  • Weakness
  • Skin rash
  • Vomiting
  • Diarrhea
  • Joint pain
  • Dizziness
  • Lightheadedness
  • Sunlight sensitivity (with thiazide diuretics)

Risks and Complications

Thiazide and loop diuretics can decrease potassium levels. Your healthcare provider may advise you to limit salt intake and increase potassium-rich foods if you take these types of diuretics.

In contrast, potassium-sparing diuretics may cause potassium levels to become too high. This can potentially lead to dangerous heart-rhythm conditions or cardiac arrest.

If you take diuretics, ask your healthcare provider if you need to have your potassium levels and kidney function checked periodically.

Diuretics could also contribute to dehydration due to fluid loss if you aren't drinking enough water.

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.

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.

Frequently Asked Questions

  • What are natural diuretics?

    Some herbs and supplements may act as natural diuretics. These include dandelion, ginger, juniper, hawthorn, and parsley. Always check with your healthcare provider before taking a supplement to make sure it's safe for you.

  • How long does it take for diuretics to work?

    It usually takes about one to two hours for diuretics to start to work.

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14 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.