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Diuretics are a type of medicine often used to treat high blood pressure.

There are different types of diuretic, and the types usually used to treat high blood pressure are called thiazide diuretics. They work by removing excess fluid from the blood. Most have names that end in ‘ide’, for example, indapamide, bendroflumethiazide, chlortalidone, cyclopenthiazide.


How do diuretics work?

Diuretics are sometimes called water tablets because they remove excess fluid from your body. They act on the kidneys, causing them to take more salt and water out of your blood to be released in your urine. With less fluid in the blood vessels, there is less pressure against your blood vessel walls.

Diuretics also allow the muscles in your blood vessel walls to relax, so your blood vessels widen. This makes it easier for your blood to flow through, lowering your blood pressure.


Who can take diuretics?

If you have high blood pressure your doctor or nurse might suggest you take medicines to lower it. It can take some trial and error to find the right one or the right combination, and diuretics are often one of the first ones you will try, either on their own or alongside another one.

They’re often suitable if you’re over 55 and of African or Caribbean descent, but can still be an option if that doesn’t apply to you.  Diuretics are usually used if another type of medicine called calcium-channel blockers are causing side effects.

If thiazide diuretics are not suitable for you, or you’re already taking three blood pressure medicines, there are other types of diuretic which might be suitable for you, called loop diuretics and potassium-sparing diuretics. 

Potassium-sparing diuretics can be used if you have low potassium levels, as other types of diuretics can lower your potassium.


When are diuretics not suitable?

Diuretics can occasionally interfere with other health problems or medicines you’re taking. This can mean that diuretics aren’t suitable for everyone, or that you will need careful monitoring. For example, if you have urinary problems, kidney or liver problems, diabetes, gout, Addison’s disease (a rare condition affecting the adrenal glands), or low potassium or sodium levels.

Your doctor will consider your overall health and any treatments you’re having before giving you any new medicines.


Do diuretics have side-effects?

All medicines can have side effects, including blood pressure medicines. It’s likely you won’t have any side effects at all with diuretics, or you might have some that are minor and don’t cause you too many problems.

If you have side effects which don’t improve and are affecting your day-to-day life, you should be able to try a lower dose or a different medicine.

Possible side effects of diuretics include:

  • needing to urinate (wee) more often
  • feeling thirsty
  • upset stomach
  • dizzy, weak, lethargic, feeling sick
  • a sudden drop in blood pressure when you go from lying ­or sitting down to standing up (postural hypotension)
  • skin rash and sensitivity to light
  • muscle cramps
  • raised uric acid levels (that can lead to kidney problems and gout)
  • raised blood sugar levels
  • problems with erections in men

Diuretics can also lower the amount of potassium, sodium and magnesium in your body, along with a rise in calcium. If these levels drop too low, this can make you weak or confused, and can cause heart problems. You will have these levels monitored with blood tests, usually once a year, if you are taking a thiazide or loop diuretic.

The leaflet that comes with your medicine will have a full list of possible side effects.


Taking diuretics

You take diuretics as a tablet, usually once a day. They can also be part of a combined tablet – where more than one medicine is combined in one tablet – for example with ACE inhibitors or angiotensin receptor blockers

It can help to take diuretics in the morning so that you don’t have to keep getting up in the night to urinate (wee).

You might need to have regular blood and urine tests to check your potassium, sodium and blood sugar levels. This is to make sure that all the chemicals in your blood stream are properly balanced.

Taking a thiazide diuretic with a beta-blocker can raise your risk of developing diabetes in the long term. If you’re taking both these types of medicines together, speak to your doctor or pharmacist about whether this is right for you.

Check with your doctor or pharmacist before taking any other medicines at the same time as diuretics, as they can interact, including medicines you buy over the counter such as painkillers and anti-inflammatories.

If you start taking high blood pressure medicines, it’s likely you will need to keep taking them for the long term. If your blood pressure stays under control for several years, you might be able to take a lower dose or stop taking them altogether.

It’s important that you don’t simply stop taking diuretics because your blood pressure will quickly rise again. Always let your doctor, nurse or pharmacist know if you’re struggling because there could be other options you can try.


Read more

Diuretics information sheet

   Download our Diuretics information sheet [PDF 14,141KB]




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