Expert reviewer Alastair Bovell, Lead Clinical Pharmacist, Bupa Cromwell Hospital
Next review due January 2020

Diuretics are medicines that act on your kidneys to make them produce more urine than usual in order to get rid of excess salts and fluids. They are often called ‘water tablets’.

This information is for you if:

  • your doctor has recently advised you to take diuretics
  • you’re currently taking diuretics and would like more information about them

An image showing a doctor talking to a patient

Why take diuretics?

Your doctor may offer to prescribe medicines called diuretics for you if you have:

They are used in some other instances too, but this topic focuses on their use for these two conditions. Here we discuss how diuretics work, how to take them, monitoring your health and information about side-effects.

How do diuretics work?

Your kidneys filter out water, salts (mainly potassium and sodium) and waste products from your blood. Most of the water and salts are reabsorbed back into your bloodstream, but some are left with the waste products to form urine.

Diuretics make your kidneys release more salts and water into your urine, stopping your body reabsorbing them back into your bloodstream. Instead, your body gets rid of the salts and water by increasing the amount of urine you produce. These medicines make you need to go to the toilet more frequently, which is why they are often called ‘water tablets’.

Getting rid of extra salts and fluid in this way decreases the amount in your bloodstream and reduces the overall volume of your blood. This lowers your blood pressure and gives your heart less work to do. This is why they are used to treat high blood pressure and oedema caused by heart failure.

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Types of diuretics

The three most common types of diuretic are:

  • thiazide and thiazide-related diuretics
  • loop diuretics
  • potassium-sparing diuretics

You might take one or you may need to take a combination.

Not all of these medicines have branded versions; some are only available as generic medicines. Some of the medicines aren’t licensed in the UK. This means the medicine may be used to treat a condition that it has not been licensed for. If this is the case for your medication, your condition won’t be listed in the patient information leaflet that comes with the medicine. A doctor can legally prescribe a medication outside the terms of its licence if he or she feels the medicine will be effective for you. Prescribing outside the license is called ‘off-label’ use.

Thiazide diuretics

Your GP may prescribe you a thiazide diuretic (eg indapamide) if you have:

  • heart failure or oedema (too much fluid in your body tissues )
  • high blood pressure and other medicines (such as angiotensin-converting enzyme (ACE) inhibitors or calcium-channel blockers) haven’t worked

Common thiazide diuretics include:

  • bendroflumethiazide (generic)
  • cyclopenthiazide (Navidrex®)
  • hydrochlorothiazide (unlicensed)

Common thiazide-related diuretics include:

  • chlortalidone or chlorthalidone (unlicensed)
  • Indapamide (Natrilix®)
  • metolazone (unlicensed)

Loop diuretics

Your GP may prescribe you a loop diuretic (eg furosemide) if you have:

  • oedema as a result of kidney failure
  • heart failure

Common loop diuretics include:

  • Bumetanide (generic)
  • Furosemide (Lasix®)
  • Torasemide (Torem®)

Potassium-sparing diuretics

Potassium-sparing diuretics are weak medicines when used alone. Your GP may prescribe you a potassium-sparing diuretic (eg amiloride) in combination with other medicines or diuretics if you have high blood pressure or heart failure. Thiazide and loop diuretics can sometimes cause you to lose too much potassium from your body. Potassium has many important roles; it helps keep your heart healthy and control the balance of fluids in your body. So, to make sure you don’t lose too much potassium, your GP may advise you to take a potassium-sparing diuretic at the same time as a thiazide or loop diuretic.

Common potassium-sparing diuretics include:

  • amiloride (Amilamont®)
  • triamterene (Dytac®)
  • spironolactone (Aldactone®)
  • eplerenone (Inspra®)

Monitoring your health

Once you’ve started taking a diuretic, you’ll need to have some health checks. These may be fairly frequent to begin with. How often will depend on which particular diuretic you’re taking. It may seem like you’re having a lot of check-ups, but this is just so your doctor can make sure the medicine is working in the right way.

If you’re taking thiazide, you will have your blood pressure, kidney function, and salt and potassium levels checked within the first four to six weeks. After that, you’ll have a check-up every six to 12 months.

With loop diuretics, you’ll have these checks sooner – within one to two weeks, or sometimes even earlier. Once everything is stable, check-ups are every six months.

With some potassium-sparing diuretics (eg spironolactone), your kidney function and electrolytes may be checked after one week, then a month, then two months and three months. After that, it’s at six, nine and 12 months but from then on, it goes down to every six months.

Will I need diuretics for the rest of my life?

Yes, it’s likely that once you start taking diuretics you’ll need to take them on a long-term basis, perhaps for the rest of your life. This is because once you have high blood pressure, it is unlikely to stay down without medicines. Following your GP’s advice about diet and excess weight loss may help reduce or reverse the need to take diuretics for some people. It’s important to continue with the lifestyle measures because they will give you benefits that are additional to those of your medicine. Your treatment is very much a combined approach and it’s important not to rely solely on your medicine.

Can anyone take diuretics?

Not everyone can take diuretics. Diuretics can make some existing conditions worse, so it’s important to tell your doctor about any condition you have. You should also mention any medicine, herbal, vitamin or mineral supplements you’re currently taking. Conditions that can be worsened with diuretics include:

  • diabetes
  • gout
  • systemic lupus erythematosus
  • liver problems
  • kidney problems

You may still be able to have the diuretic, but your doctor may monitor you more closely, or they may discuss other treatment options with you.

Diuretics aren’t recommended to treat high blood pressure in pregnancy (pre-eclampsia) because they can cause harm to you and your baby. Other medicines are recommended for this.

Some diuretics aren’t advised if your breastfeeding. Talk to your GP about this for more information.

The older you are, the more likely you are to develop side-effects from diuretics. Therefore, you may need to take a lower dose to begin with. Your GP may change the dose, depending on how well your kidneys are working.

Diuretics aren’t used to treat swelling in your legs caused by gravity – raising your legs, wearing compression stockings and moving your legs more are usually able to help with this.

Interactions with medicines, food and drinks


If you need to take a diuretic and are already taking other medicines, some of your medicines may interact with each other. These interactions may affect how one or more of your medicines work, and they may also cause side-effects.

There is a list of interacting medicines on the patient information leaflet that comes with your medicine, but medicines that may be affected by diuretics include:

  • medicines that act on your heart (eg digoxin)
  • antibiotics (eg vancomycin)
  • beta-blockers (eg sotalol)
  • anti-arrhythmics (eg flecainide)
  • NSAIDs (eg ibuprofen)

Food and drink

It’s important not to eat too much salt if you’re taking a diuretic. Too much salt in your diet can affect how diuretics work. You should also steer clear of salt substitutes if you’re taking potassium-sparing diuretics.

Be careful when drinking alcohol while taking diuretics because this may cause your blood pressure to fall. Alcohol has a diuretic effect of its own, by blocking the release of an antidiuretic hormone (called AKA ADH or vasopressin). This may lead to lower blood pressure. In addition, drinking large quantities of solute-poor liquids (eg beer or tea) may overload your body with fluid. This can cause problems.

Vitamin and mineral supplements

It’s important not to take potassium supplements at the same time as potassium-sparing diuretics. This is because the level of potassium in your blood could then become very high. This leads to a condition called hyperkalaemia which may give you symptoms such as:

  • muscle weakness
  • irregular heartbeat
  • tiredness
  • chest pain
  • shortness of breath

This can be a medical emergency.

You may also need to stop taking calcium supplements. This is because diuretics can increase the level of calcium in your body, which may in turn affect your kidneys, heart or brain.

It’s important that you tell your GP about all the medicines you’re taking, both prescribed and over-the-counter. He or she can then advise you about what interactions and side-effects they may have with a diuretic. Always read the patient information leaflet that comes with your medicine.

Side-effects of diuretics

Side-effects are unwanted symptoms caused by taking a medicine. Not everyone gets them but if you do, you may find that they ease as your body gets used to the medicine. If side-effects are causing you problems, speak to your GP or pharmacist.

Because there are different types of diuretic, it’s not possible to say which side-effects are the most common, it depends on the specific type of diuretic you’re taking. The best way to find out is to speak to your pharmacist or read the patient information leaflet that comes with your medicine.

As an indication though, these are some of the side-effects that have been reported with taking diuretics. They include:

  • low blood pressure when you get up from sitting or lying down to standing
  • potassium loss which can give you muscle weakness, cramps and spasms
  • needing to pass urine more often or being unable to urinate
  • electrolyte disturbances including decreased or increased amounts of calcium, magnesium and sodium in your blood
  • mild problems with your digestion
  • gout
  • raised blood sugar levels
  • skin rashes and itchy skin
  • headache
  • feeling dizzy
  • low libido and erectile dysfunction
  • dehydration (see our FAQ about hydration and diuretics for information and advice about this)
  • pancreatitis
  • rapid or irregular heart beat (palpitations)
  • tinnitus and hearing problems (your doctor may arrange a hearing test to monitor this)

If you’re having side-effects, give your new medicine a chance and wait a few days to see if they ease. If they continue and you’re feeling unwell or concerned, contact your doctor or pharmacist for advice and help.

Frequently asked questions

  • If you’re taking a diuretic for severe heart failure, it’s important to keep your fluid intake balanced. You may need to restrict your fluid intake to help relieve symptoms of heart failure; for example having less than 1.5L – 2L a day. But at the same time, you don’t want to restrict it too much because of the risk of dehydration. Your doctor can help you with this. They will suggest how much fluid to drink. And, if you feel very thirsty, light headed or dizzy – contact your doctor. This could be a sign of low blood pressure or that the volume of blood circulating around your body has decreased. Your doctor may need to reduce the dose of your medicine.

    Some diuretics are more powerful than others and can cause more dramatic effects. For example a combination of a thiazide and a loop diuretic (for heart failure) can cause a big increase in urine production, which can result in dehydration and other problems. To minimise the chance of this happening, you’ll have some tests to check your kidney function early on (within the first five days).

    It’s important to be aware of dehydration. This is an important side-effect which can cause kidney damage. If you develop diarrhoea and vomiting, stop taking the diuretic for one to two days and keep drinking fluids as you normally would.

    This will help you to avoid becoming dehydrated, getting low blood pressure or kidney problems. However, if after two days you still feel unwell, you should see your GP for advice.

  • Because diuretics are used to reduce the amount of fluid in your body, many women wonder if diuretics could be used to reduce bloating (water retention) before and during their period. Bloating can be an uncomfortable and annoying symptom of premenstrual syndrome (PMS). It can make you feel heavy and your stomach may feel or look swollen. It can affect how you feel and your confidence levels. However, diuretics aren’t recommended by doctors as a treatment for this.

    Some research studies have investigated how well diuretics reduce bloating caused by premenstrual syndrome (PMS). However, there’s not enough research or proof to suggest that diuretics, such as spironolactone, may help in treating bloating during your period. And so diuretics are not officially recommended as a treatment for bloating caused by PMS.

    Diuretics are strong medicines and taking them gets rid of essential minerals – such as potassium – that you need for good general health. There are other ways that may reduce bloating caused by water retention during your period, many of them natural.

    If bloating is particularly uncomfortable during your period, see your GP for advice. There are medical treatments you can take that may ease symptoms of PMS. Your GP can talk to you about the best ways to reduce bloating.

  • Glaucoma is a term used to describe a group of eye conditions where your optic nerve becomes damaged, causing your vision to get worse. Your optic nerve is a nerve that connects your eye to your brain. The damage to the optic nerve is caused by an increase in pressure in your eye, caused by fluid that is naturally in your eye not draining away properly.

    The aim of treatment for glaucoma is to reduce the pressure in your eye. Different types of medicine are available to treat glaucoma, including diuretics. These may be prescribed as eye drops or tablets.

    Your GP may recommend a weak diuretic, such as acetazolamide. It works by reducing the amount of fluid that your eye produces; this helps to reduce the pressure to a healthy level.

    Always ask your GP for advice and read the patient information leaflet that comes with your medicine.

  • Generally you don’t need to drink more fluids if you’re on a diuretic (unless you’re also on a fluid-restricted diet). Just drink as much as you normally do. If you’re thirsty, have a drink of water.

    If you develop diarrhoea and vomiting, stop taking the diuretic for one to two days until you feel better and are eating and drinking normally again. Keep up your fluid intake too. If after two days you still feel unwell, you should see your GP for advice.

    If you’re dehydrated and have vomiting and/or diarrhoea you might lose quite a lot of salt. Unless you’re on a restricted salt diet, you can use rehydration salt sachets to help replace the salts you’re losing.

    It is important to be aware of dehydration. This is an important side-effect which can cause kidney damage. If you develop diarrhoea and vomiting, stop taking the diuretic for one to two days and keep drinking fluids as you normally would.

    This will help to avoid becoming dehydrated, getting low blood pressure or kidney problems. However, if after two days you still feel unwell, you should see your GP for advice.

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Related information

    • Chronic heart failure in adults: management. National Institute for Health and Care Excellence (NICE), August 2010.
    • Heart failure. The MSD Manuals., Last full review/revision September 2013
    • Diuretics. NICE British National Formulary., reviewed January 2017
    • Hypertension in adults: diagnosis and management. National Institute for Health and Care Excellence (NICE) August 2011.
    • Your kidneys and how they work. National Institute of Diabetes and Digestive and Kidney Diseases., published March 2014
    • Diuretics. PatientPlus., last checked 30 December 2016
    • Drugs for hypertension. The MSD Manuals., Last full review/revision July 2016
    • Alkapamid., accessed 16 August 2016
    • Heart failure – chronic., last revised March 2016
    • Medicines for high blood pressure. Blood Pressure UK., accessed 20 September 2016
    • Hyperkalemia. The MSD Manuals., last full review/revision April 2016
    • Avoid food–drug interactions. FDA., accessed 25 August 2016
    • Hyperkalemia. Medscape., last updated 11 January 2016
    • Hypercalcemia. Medscape., last updated 2 August 2016
    • Glaucoma. NICE Clinical Knowledge Summaries., last revised January 2016
    • Treatment of glaucoma. NICE British National Formulary., reviewed January 2017
    • Carbonic anhydrase inhibitors and systemic drugs. NICE British National Formulary., reviewed January 2017
    • Premenstrual syndrome. NICE Clinical Knowledge Summaries., last revised March 2014

  • Reviewed by Natalie Heaton, Specialist Health Editor, Bupa Health Content Team, January 2017
    Expert reviewer Alastair Bovell, Lead Clinical Pharmacist, Bupa Cromwell Hospital
    Next review due January 2020

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