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Diuretics

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 excess water.

The most common reasons you may need to take a diuretic are if you have:

  • high blood pressure
  • too much fluid in your body tissues (known as oedema), as a result of heart failure, which is when your heart loses its ability to pump blood efficiently through your body
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Details

  • Types What are the main types of diuretic?

    The three most common types of diuretic are:

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

    Thiazide and related diuretics

    Your GP may prescribe you a thiazide or related diuretic (eg indapamide) if you have high blood pressure (particularly if you're over 55 or if you’re of African-Caribbean origin), mild heart failure or oedema.

    If your blood pressure isn’t controlled with a thiazide alone, you may need to take another medicine with the thiazide. For example, your GP may prescribe an angiotensin-converting enzyme inhibitor or an angiotensin-receptor blocker. If this still fails to control your blood pressure, your GP may prescribe a calcium channel blocker.

    Thiazide diuretics can sometimes cause you to lose too much potassium from your body. Potassium has many important roles, such as to keep your heart healthy and control the balance of fluids in your body. Your doctor may therefore need to give you a potassium supplement or a potassium-sparing diuretic to take at the same time.

    Loop diuretics

    These medicines are the most powerful type of diuretic. Loop diuretics increase the amount of urine your kidneys produce very quickly. Your GP may prescribe you a loop diuretic (eg furosemide) if you have a condition called peripheral oedema, which is when you have too much fluid in your legs.

    If you’re taking a loop diuretic, you may lose too much potassium from your body. Your GP may therefore need to give you a potassium supplement or a potassium-sparing diuretic to take as well.

    Potassium-sparing diuretics

    These medicines are mild diuretics. Potassium-sparing diuretics are usually used together with a thiazide or loop diuretic to stop you losing too much potassium from your body.

    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?

    Diuretics work by changing the filtration process in your kidneys.

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

    Diuretics work by reducing the amount of sodium and water that your body re-absorbs back into your bloodstream. This increases the amount of urine your body produces and decreases the amount of fluid left in your bloodstream. The overall volume of your blood is therefore 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, although some are also available as injections. Thiazide diuretics usually have an effect for 12 to 24 hours, so 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 complete their effect within six hours so you can have these twice a day if necessary without them disturbing your sleep.

    As some diuretics can cause your blood potassium levels to fall, your GP may advise you to take a potassium supplement or eat foods with plenty of potassium in them. 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.

    Special care for elderly people

    If you’re elderly, you may need to take a lower diuretic dose to begin with. This is because you’re more likely to be affected by the side-effects that diuretics cause. Your doctor may then change the dose, depending on how well your kidneys are working.

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  • Side-effects Side-effects of diuretics

    Side-effects are the unwanted effects of taking a medicine. If you have side-effects, it’s important to talk to your doctor or healthcare professional who prescribed your medicine – don’t stop taking it before you speak to him or her.

    Side-effects of diuretics include:

    • mild gastro-intestinal problems, such as 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
    • altered levels of salts in your body, such as low levels of potassium (hypokalaemia) and sodium (hyponatraemia)

    Less common side-effects of diuretics include:

    • gout (a condition that causes pain and swelling in your joints)
    • impotence in men (the inability to achieve or sustain an erection during sex)
    • skin rashes
    • headaches
    • certain blood disorders, which can make you more likely to get infections

    This section doesn't include every possible side-effect of diuretics. Please read the patient information leaflet that comes with your medicine for more information.

  • Interactions Interactions of diuretics with other medicines

    It’s important not to take potassium supplements at the same time as potassium-sparing diuretics, unless your GP recommends it.

    If you’re taking other medicines for a heart problem, low levels of potassium caused by a diuretic may cause you to have an irregular heartbeat.

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

  • 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 (Non-proprietary)
    xipamide Diurexan
    Loop diuretics  
    furosemide/frusemide Lasix
    bumetanide (Non-proprietary)
    torasemide Torem
    Potassium-sparing diuretics  
    amiloride Amilamont
    triamterene Dytac
  • FAQs FAQs

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

    Answer

    Diuretics can interact with a number of different medicines. Before you take a diuretic, it’s important to tell your doctor if you’re taking any medicines (prescribed or bought at a pharmacy) or herbal, vitamin and mineral supplements. This will help to prevent any drug interactions, which may be harmful or could affect the effectiveness of your diuretic or other medicines.

    Explanation

    Diuretics are often prescribed in combination with other medicines, particularly ones that you might need for heart problems. If you need to take a diuretic and are already taking other medicines, there is a chance that your medicines may interact with each other. These interactions may affect the effectiveness of one or more of your medicines and may cause some of your symptoms to return. 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.

    Medicines that are affected by diuretics include:

    • some drugs that act on your heart (eg digoxin)
    • some antibiotics (eg vancomycin)
    • some beta-blockers (eg sotalol)
    • some anti-arrhythmics (eg flecainide)
    • lithium

    If you’re prescribed more than one type of diuretic, for example a thiazide diuretic and a loop diuretic, this can upset the balance of minerals in your body and lead to low levels of potassium (hypokalaemia). This may cause you to have an irregular heartbeat.

    You may need to be careful drinking alcohol while taking diuretics as this may cause your blood pressure to decrease below your usual levels. This is because alcohol is a diuretic. You may also need to stop taking certain vitamin supplements, for example, calcium or vitamin D supplements due to the risk of high calcium levels in your blood.

    It’s important that you tell your doctor 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 ask your doctor for advice and read the patient information leaflet that comes with your medicine.

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

    Answer

    Glaucoma is a term used to describe a group of eye conditions where your optic nerve becomes damaged and your vision deteriorates. An increase in pressure within your eye or a weakness in your optic nerve, or both, can cause this damage. If you have glaucoma, taking a diuretic can help to reduce the amount of fluid in your eye and maintain a healthy eye pressure.

    Explanation

    Your eye is filled with a watery substance (aqueous humour), which creates pressure to maintain its shape. In a healthy eye, this fluid constantly flows in and out of your eye to nourish it. Eye pressure is maintained by this fluid moving back and forth between your eye and your bloodstream at the same rate.

    The aim of treatment for glaucoma is to reduce the pressure in your eye. Different types of medicine are available to treat glaucoma. These include beta-blockers, prostaglandins and diuretics. Some of these are prescribed as eye drops rather than tablets. Your doctor may recommend a weak diuretic, such as acetazolamide. Acetazolamide works by reducing the production of fluid so that your eye pressure can be reduced to a healthy level.

    Always ask your doctor 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?

    Answer

    A diuretic such as spironolactone may help to relieve symptoms such as bloating and mood swings during your period. However, there is limited evidence that diuretics are helpful and diuretics aren’t regularly prescribed to remove excess fluid from your body during your period.

    Explanation

    Bloating has several causes, but is typically caused by water retention resulting from the action of your hormones just before your period starts. Other causes include:

    • too much salt in your diet
    • regular use of some common medicines (eg contraceptive pill)
    • periods of immobility (eg standing for long periods of time)

    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. Your GP can give you further advice on the best ways to reduce bloating.

    If bloating is particularly uncomfortable during your period, your GP may prescribe you a potassium-sparing diuretic, such as spironolactone.

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

  • Resources Resources

    Further information

    Sources

    • Faris RF, Flather M, Purcell H, et al. Diuretics for heart failure. Cochrane Database of Systematic Reviews 2012, Issue 2. doi:10.1002/14651858.CD003838.pub3
    • Your medicines explained. British Heart Foundation. www.bhf.org.uk, accessed 14 November 2012
    • Joint Formulary Committee. British National Formulary. 64th ed. London: British Medical Association and Royal Pharmaceutical Society of Great Britain; 2012
    • Hypertension – clinical management of primary hypertension in adults. National Institute for Health and Care Excellence (NICE). www.nice.org.uk, published August 2011
    • An everyday guide to living with heart failure. British Heart Foundation. www.bhf.org.uk, published 29 March 2010
    • Other diuretics. British Hypertension Society. www.bhsoc.org, published December 2008
    • 2010 comprehensive heart failure practice guideline: diuretic therapy. Heart Failure Society of America. www.heartfailureguideline.org, published 2010
    • Cadwallader AB, de la Torre X, Tieri A, et al. The abuse of diuretics as performance-enhancing drugs and masking agents in sport doping: pharmacology, toxicology and analysis. Br J Pharmacol 2010; 161(1):1–16. doi:10.1111/j.1476-5381.2010.00789.x
    • Thiazide and thiazide-like diuretics. British Hypertension Society. www.bhsoc.org, published December 2008
    • Potassium. Food Standards Agency. www.eatwellscotland.org, accessed 14 November 2012
    • Glaucoma and ocular hypertension. Prodigy. www.prodigy.clarity.co.uk, published September 2010
    • NHMRC guidelines for the screening, prognosis, diagnosis, management and prevention of glaucoma. National Health and Medical Research Council. www.nhmrc.gov.au, published 2010
    • Premenstrual syndrome – evidence. Prodigy. www.prodigy.clarity.co.uk, published December 2009
    • Premenstrual syndrome and premenstrual dysphoric disorder. The American College of Obstetricians and Gynecologists. www.acog.org, published 2009
    • Physical symptoms. National Association for Premenstrual Syndrome. www.pms.org.uk, published 2007
    • Premenstrual syndrome. The American College of Obstetricians and Gynecologists. www.acog.org, published May 2011
    • Weight loss. Mayoclinic. www.mayoclinic.com, published 11 October 2011
    • Aprinox 2.5 and 5mg tablets. EMC Medicine Guides. www.medicines.org.uk, published 29 November 2006
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    Produced by Rachael Mayfield-Blake, Bupa Heath Information Team, November 2012.

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