What You Need to Know About Diuretics

Diuretics, also known as “water pills,” increase the flow of urine and help your kidneys remove salt from your 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.

What Do Diuretics Treat?

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

• High blood pressure
• Congestive heart failure
• Pulmonary edema
• Glaucoma
• Liver disease, such as cirrhosis
• Some kidney conditions, such as kidney stones
• Edema (swelling) in the legs, abdomen, and lungs

In some cases, diuretics may need to be taken long-term. In others, they can be discontinued once symptoms improve.

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 milder than a 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 kidney 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 these drugs act as mild diuretics.

SGLT2 drugs like Invokana (canagliflozin) and Farxiga (dapagliflozin) are often used to treat diabetes because 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 Lasix (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 the nephrons, the parts of the kidney responsible for filtering fluids and waste that make up urine. 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 a first-line treatment (i.e., one of the first recommended treatments) for high blood pressure (hypertension). In fact, a 2019 study found that thiazides are more effective as a first-line treatment of hypertension than ACE inhibitors, another common treatment.

When the 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 help your kidneys remove salt from your body. This helps your body produce more urine. Flushing out the excess sodium helps reduce blood volume, which can lower blood pressure and help your heart pump more efficiently.

Many diuretics work by acting on the kidneys’ nephrons, the parts of the kidney responsible for filtering fluids and waste that make up urine. Each of your kidneys has about a million nephrons. Diuretics limit the amount of sodium that can be absorbed by nephrons.

Some diuretics work by inhibiting the reabsorption of water. They do this by blocking receptors for vasopressin, the hormone responsible for maintaining water levels in your body.

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

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.