Diuretics (Water Pills) for High Blood Pressure

Medically Reviewed by Jabeen Begum, MD on May 30, 2024
Written by Kathryn Whitbourne
8 min read

Diuretics are commonly used to control blood pressure. Also known as "water pills," these drugs help your kidneys get rid of extra water and salt from your body through your urine. Because you have less fluid in your blood vessels, your blood pressure goes down. Diuretics allow your blood vessels to widen, which makes it easier for blood to flow and easier for your heart to pump.

Diuretics are also given if you have too much fluid in other parts of your body.

You might be prescribed a water pill with more than one type of diuretic inside. Or you might be prescribed a diuretic and another type of medication to treat your health issue. Examples of diuretics include:

Diuretics come in different types: thiazide, loop, potassium-sparing, osmotic, and carbonic anhydrase inhibitors.

Thiazide diuretics

These are among the most commonly prescribed diuretics for treating high blood pressure. They cause your kidneys to remove extra water and salt. One downside is that they also cause you to lose potassium. Examples include:

  • Chlorthalidone (Hygroton, Thalitone)
  • Hydrochlorothiazide, or HCTZ (Microzide, Oretic) 
  • Indapamide (Lozol)

Loop diuretics

These are not usually the first choice for treating high blood pressure. Instead, they're used for other conditions such as getting rid of extra fluid in your legs and lungs if you have heart failure. (Heart failure is associated with your body having too much water and salt.) 

They're also used to treat kidney problems (nephrotic syndrome), liver disease (cirrhosis), and swelling (edema). Loop diuretics are more powerful than thiazide diuretics, meaning you'll be peeing a lot. They're very useful in emergencies. These pills also remove potassium along with water and salt from your kidneys. Examples include:

  • Bumetanide (Bumex)
  • Ethacrynic acid (Edecrin)
  • Furosemide (Lasix)
  • Torsemide (Demadex)

Potassium-sparing diuretics

These help you keep potassium while your kidneys get rid of excess water and salt. They're considered to be weak, so they're usually given along with other types of diuretics. Examples include:

  • Amiloride (Midamor)
  • Eplerenone (Inspra)
  • Spironolactone (Aldactone, Carospir)
  • Triamterene (Dyrenium)

Osmotic diuretics

Mostly given intravenously (by vein), these are used to get rid of fluid in the brain or the eye, or to treat low urine output resulting from kidney failure. The main drug in this category is mannitol (Osmitrol).

Carbonic anhydrase inhibitors

These are mainly used to treat glaucoma, but also altitude sickness, epilepsy, and idiopathic intracranial hypertension (increased pressure around your brain due to fluid buildup in your skull). These drugs reduce the activity of an enzyme in the kidneys called carbonic anhydrase. They prevent the reabsorption of bicarbonate, making the urine more alkaline (basic). Too much bicarbonate in the body leads to many health problems. 

In the eyes, carbonic anhydrase inhibitors treat glaucoma by reducing the production of aqueous humor (a clear fluid in front of the eyeball), which lowers pressure in the eye. The diuretic effects are mild, so these drugs are not often used for this purpose. Examples include:

  • Acetazolamide (Diamox)
  • Dichlorphenamide (Keveyis)
  • Methazolamide (Neptazane)

Your doctor may recommend a diuretic if you have:

  • Edema. Diuretics lessen the swelling that usually happens in the legs.
  • High blood pressure. Thiazide diuretics lower blood pressure, lowering your chance of a stroke or heart attack.
  • Heart failure. Diuretics ease swelling and congestion in the lungs. You’ll usually get a loop diuretic for heart failure.
  • Kidney problems. Diuretics help you retain less water.
  • Liver problems. If you have cirrhosis, a diuretic can ease the fluid buildup.
  • Glaucoma. Diuretics will help reduce the pressure in your eye.
  • Some diuretics are sulfa drugs, so they could cause a reaction if you're allergic.
  • Older people tend to have more side effects such as fainting and dizziness from dehydration. You'll need to work closely with your doctor.
  • If you’re breastfeeding, most diuretics are fine to take, with some precautions. Talk with your doctor.
  • Tell your doctor if you have diabetes, kidney disease, liver disease, or gout. Diuretics can increase blood sugar levels and insulin resistance, so you have to be careful if you're diabetic. Diuretics can also raise uric acid levels, which is a problem if you have gout. Low potassium levels are also likely to cause heart rhythm problems, especially when digoxin is also taken.
  • Kids can safely take them, but they need smaller doses. The side effects are similar to adults. But potassium-sparing diuretics can cause low levels of calcium, which could hurt bone development.
  • If you only need one dose a day, take your diuretic in the morning so you can sleep through the night instead of getting up to go to the bathroom. Take it with your breakfast or soon after.
  • If you’re taking more than one dose a day, take the last one no later than 4 p.m.
  • Avoid alcohol and medicines to help you sleep. They may make side effects worse.
  • Follow the directions on the label.
  • Weigh yourself at the same time every day (on the same scale) and write down your weight. Call your doctor if you gain 3 pounds in 1 day or 5 pounds in 1 week.
  • Keep all your doctor and lab appointments so your response to this medicine can be tracked.

To avoid a potential problem, tell your doctor and pharmacist about all the medicines you're taking, including:

Also, tell them about any other medical problems you may have. 

Your doctor will want to regularly check your blood pressure as well as test your blood and urine for levels of specific minerals and to see how well your kidneys are working. 

Some diuretics may require you to avoid or eat certain foods. Follow your doctor's advice, which may include:

  • A low-salt diet
  • A potassium supplement

On the other hand, if you're taking a potassium-sparing diuretic, your doctor may want you to avoid potassium-rich products, such as: 

  • Bananas
  • Sweet potatoes
  • Spinach
  • Lentils
  • Salt substitutes
  • Low-sodium milk

Tell your doctor if you’re taking:

Diuretics are often prescribed with other drugs. If you have more side effects when you take them together, contact your doctor. You may need to change their timing.

Here are some of the side effects of water pills:

  • The water that comes out of your body has to go somewhere, so you can expect to be peeing more, often for several hours after a dose.
  • You run the risk of getting dehydrated, and simply drinking more fluids may not be enough. Call your doctor if you're very thirsty or have a very dry mouth, your pee is a deep yellow, you aren't peeing much or getting constipated, or you have a bad headache.
  • You may have extreme tiredness or weakness. These should ease as your body gets used to the medicine. Call your doctor if these symptoms hang around. That could mean your dose needs to be adjusted.
  • You may feel dizzy or lightheaded (especially when you stand up) if your blood pressure has dropped too low or if you're getting dehydrated.
  • Your blood chemistry can get thrown off. You could have too little or too much sodium or potassium in your system. This can make you tired or weak or give you muscle cramps or a headache. It's rare, but your heart may speed up (over 100 beats a minute). You might start throwing up because of a dangerously low potassium level.

Diuretics and potassium loss

Diuretic medications cause your kidneys to release potassium along with water and sodium. Too low levels of potassium can create muscle weakness, cramping, and an irregular heartbeat. The medical term for low blood potassium is hypokalemia. The normal potassium level should be 3.5 to 5.2 milliequivalents per liter (mEq/L). If your level is less than 3 mEq/L, you have severe hypokalemia. Signs of hypokalemia include:

  • Constipation
  • Fatigue
  • Heart murmurs
  • Numbness and tingling

Treatment is usually a potassium supplement and/or switching your diuretic. You can also eat more potassium-rich foods, but usually, that's not enough to counteract the effects of a diuretic.

Diuretics and hypotension

Too much fluid loss can make you dizzy when you stand up. This is called postural hypotension. Hypotension is a medical term for low blood pressure. Signs of hypotension include:

  • Dizziness
  • Blurred vision
  • Fainting and fatigue

If your blood pressure is too low, let your doctor know. They may change your diuretic medication or prescribe a drug to treat your hypotension.

What happens when you stop taking water pills?

Usually, your high blood pressure or heart problem will come back. One study of elderly patients on long-term diuretic treatment found that withdrawing water pills mostly led to symptoms of heart failure or increases in blood pressure to hypertensive levels. Stopping water pills requires careful monitoring from your doctor, especially during the first month.

Some of the herbs said to be natural diuretics are ginger, parsley, hawthorn, dandelion, hibiscus (roselle), and juniper. Few of these have been studied scientifically or with conclusive results. 

For instance, a 1-day study on the effects of dandelion found that all 17 participants experienced increased urination within 5 hours of taking the first dose of dandelion extract. There was also an increase after the second dose, but no change after the third dose.

Coffee and tea are natural diuretics because of the presence of caffeine, a chemical that increases the production of pee. But the diuretic effects are pretty mild and balanced out by the fluid you take in when you have these beverages.

Other natural ways of losing water are by sweating during exercise and eating fruits and vegetables, such as watermelon, cucumbers, grapes, asparagus, and pineapple. You can also watch your salt intake. But if you have high blood pressure, these methods may not be enough to lower it. Talk to your doctor before deciding to swap out your prescription water pill for a natural diuretic.

Call your doctor or nurse if you have:

Also, call them if you have any other symptoms that concern you.

Diuretics (water pills) are often given to people with high blood pressure to allow them to get rid of excess salt and water in their bodies. This lets their blood vessels widen and their hearts pump more easily, thus lowering their pressure. Most water pills have some side effects, such as loss of too much potassium, an electrolyte your body needs to prevent muscle weakness and irregular heartbeat. Doctors can counteract that by giving you a potassium supplement.

What is the most common side effect of diuretics?

The most common side effect is frequent urination (peeing).

How quickly do diuretics lower blood pressure?

The diuretics may start to work within an hour, but it may take a few weeks for your high blood pressure levels to start coming down.

Is coffee a diuretic?

Yes, because it contains caffeine. But it's a pretty weak diuretic and its effects are balanced out by the fluid intake of the beverage itself.