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Diuretics are medicines that remove water from your body by increasing the amount of urine your kidneys produce. They are often known as 'water tablets' because they remove extra water from your body

You may need to take a diuretic if you have:

  • high blood pressure
  • too much fluid in your body tissues (known as oedema) as a result of heart failure
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  • Types What are the main types of diuretic?

    The three most common types of diuretics are:

    • thiazide diuretics
    • loop diuretics
    • potassium-sparing diuretics

    Potassium has many important roles; it helps keep your heart healthy and control the balance of fluids in your body. Thiazide and loop diuretics can sometimes cause you to lose too much potassium from your body. So your GP may advise you to take a potassium supplement or a potassium-sparing diuretic at the same time.

    Thiazide diuretics

    Your GP may prescribe you a thiazide diuretic (eg indapamide) if you have mild heart failure or oedema. You may also be advised to take a thiazide diuretic if you have high blood pressure and other treatments haven’t worked. For example, you may be prescribed a thiazide diuretic if treatments such as angiotensin-converting-enzyme (ACE) inhibitors or calcium-channel blockers haven’t helped.

    Loop diuretics

    Loop diuretics are very powerful diuretics. They increase the amount of urine your kidneys produce very quickly. Your GP may prescribe you a loop diuretic (eg furosemide) if you have oedema as a result of kidney failure. Your GP might also prescribe you a loop diuretic if you have had heart failure. If you’re taking this type of diuretic, it’s important to contact your GP if you have any diarrhoea or vomiting. This is because they can make you dehydrated. If you have any questions, or would like more information, speak to your GP for advice.

    Potassium-sparing diuretics

    Potassium-sparing diuretics are weak medicines on their own. Your GP may also prescribe you a potassium-sparing diuretic (eg amiloride) in combination with other medicines if you have high blood pressure or heart failure.

  • How they work How do diuretics work?

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

    Diuretics work by reducing the amount of sodium and water that your body reabsorbs. This increases how much urine your body produces and decreases the fluid left in your bloodstream. This means the overall volume of your blood is reduced, which gives your heart less work to do and helps to reduce your blood pressure. This is why diuretics are used to treat heart failure and high blood pressure.

  • Taking the medicine How to take diuretics

    You can take most diuretics as tablets. If you have severe, acute (sudden) heart failure, you might be given a diuretic (eg furosemide) as an injection into your vein.

    The effect of thiazide diuretics usually lasts for 12 to 24 hours. It’s best to take them in the morning so that the extra urine your kidneys produce doesn’t interfere with your sleep.

    Loop diuretics work for about six hours, so if you need to, you can take them twice a day without them disturbing your sleep.

    To help keep your potassium levels healthy, your GP may advise you to take a potassium supplement or a potassium-sparing diuretic as well. Your GP may also advise you to eat foods with plenty of potassium in them, as they may help to control the balance of fluids in your body. Bananas, milk and fish are all good sources of potassium.

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

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  • Special care Special care

    The older you are, the more likely you are to develop side-effects of 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.

  • Side-effects Side-effects of diuretics

    Side-effects are unwanted symptoms caused by taking a medicine. If you have side-effects, it’s important to talk to the GP who prescribed your medicine before you stop taking it.

    This section doesn't include every side-effect you can get from taking diuretics. Please read the patient information leaflet that comes with your medicine for more information. Some of the main side-effects of diuretics may include:

    • dehydration, which may cause kidney damage
    • a drop in the levels of potassium and sodium in your body
    • feeling sick
    • a fall in blood pressure that is related to posture (postural hypotension), which causes you to feel faint or dizzy when you stand up
    • erectile dysfunction
    • skin rashes
    • headaches
    • certain blood disorders, which can make you more likely to get infections
    • gout (a condition that causes pain and swelling in your joints)

    If you develop diarrhoea and vomiting while taking a diuretic, stop taking it for one to two days until you feel better. If after two days you still feel unwell, you should see your GP for advice.

  • Interactions Interactions of diuretics with other medicines

    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 can become very high, which can lead a number of side-effects including:

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

    Check with your GP or pharmacist before you take any other medicines or herbal remedies at the same time as a diuretic. For more information about interactions of diuretics, see our FAQs section.

  • Common names Names of common diuretics

    Examples of the main types of diuretics are shown in the table below. 

    All medicines have a generic name. Many medicines also have one or more brand names. Generic names are in lower case, whereas brand names start with a capital letter.

    Generic name Examples of common brand names
    Thiazide and related diuretics  
    bendroflumethiazide Aprinox
    chlortalidone/chlorthalidone Hygroton
    cyclophenthiazide Navidrex
    indapamide Natrilix
    metolazone Metolazone
    xipamide Diurexan
    Loop diuretics  
    furosemide Lasix
    torasemide Torem
    Potassium-sparing diuretics  
    amiloride Amilamont
    triamterene Dytac
    spironolactone Aldactone
    eplerenone Inspra
  • FAQs FAQs

    I've been diagnosed with glaucoma. Why has my doctor prescribed a diuretic?


    If you have glaucoma, the pressure in your eye may be higher than usual. This can happen if there’s too much fluid produced in your eye.

    Taking a diuretic may help to reduce the amount of fluid in your eye. It may also help to keep the pressure in your eye healthy.


    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. An increase in pressure within your eye or a weakness in your optic nerve, or both, may cause this damage.

    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 production of fluid so that your eye pressure can be reduced to a healthy level.

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

    I regularly suffer from bloating when I’m having my period. Would diuretics help?


    Some research studies have investigated how well diuretics reduce bloating. However, there’s very little proof to suggest that diuretics, such as spironolactone, may help in treating bloating during your period.


    Bloating is when you have too much fluid in your body. If you’re a woman, it can occur before and during your period.

    Bloating can be caused by a number of things, such as:

    At the moment, doctors aren’t sure how well diuretics reduce bloating. This is because there’s very little proof suggesting that diuretics are helpful in treating bloating.

    However, you may be able to control bloating by doing regular exercise or changing your diet. For example, you could reduce the amount of salt you eat.

    If bloating is particularly uncomfortable during your period, see your GP for advice. He or she can talk to you about the best ways to reduce bloating.

    Are there any medicines, supplements, foods or drinks I shouldn't have if I'm taking diuretics?


    Diuretics may interact with a number of different medicines. Before you take a diuretic, it’s important to tell your GP if you’re taking any other medicines or herbal, vitamin and mineral supplements.


    Diuretics are sometimes prescribed in combination with other medicines. 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. The interactions may also cause side-effects. You may be at increased risk from medicine interactions if you’re elderly or have kidney or liver problems.

    Some of the 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)

    If you’re prescribed more than one type of diuretic, for example a thiazide diuretic and a loop diuretic, this may cause the levels of potassium in your body to decrease (hypokalaemia). Potassium is important as it helps to keep your heart healthy and control the balance of fluids in your body.

    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. Be careful when drinking alcohol while taking diuretics as this may cause your blood pressure to fall.

    You may also need to stop taking certain vitamin supplements, for example, calcium or vitamin D 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.

  • Resources Resources

    Further information


    • Diuretics. PatientPlus., published 11 June 2013
    • Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press., accessed 6 May 2014 (online version)
    • Martin, E. Concise colour medical dictionary. 3rd ed. Oxford: Oxford University Press, 2002:480 (printed version)
    • Drug cabinet: Diuretics. British Heart Foundation., accessed 6 May 2014
    • Hypertension: clinical management of primary hypertension in adults. National Institute for Health and Care Excellence (NICE), 2011.
    • Anti-hypertensive drug treatment. NICE Pathways. NICE., accessed 31 October 2014
    • Diuretics − blood pressure medication. Blood Pressure UK., Published May 2009
    • Rang H, Dale M, Ritter J, et al. Pharmacology. 5th ed. London: Churchill Livingstone, 2003:362−5
    • Potassium. Food Standards Agency., accessed 6 May 2014
    • Acute kidney injury. PatientPlus., published 13 September 2013
    • Gout. PatientPlus., published 18 October 2013
    • Heart failure − chronic. NICE Clinical Knowledge Summaries., published November 2010
    • Hyperkalaemia. PatientPlus., published 12 November 2013
    • Glaucoma. NICE Clinical Knowledge Summaries., published September 2010
    • Glaucoma. Royal National Institute of the Blind., accessed 31 October 2014
    • Primary Open-angle Glaucoma. Patient Plus., published 8 November 2013
    • Premenstrual syndrome. NICE Clinical Knowledge Summaries., published March 2014
    • Premenstrual syndrome. The American College of Obstetricians and Gynaecologists., accessed 29 May 2014
    • Abdominal distention and bloating. PatientPlus., published 21 March 2013
    • Premenstrual syndrome. PatientPlus., published 20 April 2012
    • Premenstrual syndrome and premenstrual dysphoric disorder. The American College of Obstetricians and Gynaecologists., accessed 29 May 2014
    • Hypercalcaemia. NICE Clinical Knowledge Summaries., published August 2010
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