Diuretics

Diuretics are a type of medication that is commonly used to treat high blood pressure. They work by increasing the amount of salt and water that your body puts out in urine.

Salt makes your body retain water, and this build-up of fluid raises your blood pressure. Diuretics act on your kidneys by making them increase the amount of salt they put out in your urine. The salt brings out water with it, which lowers your blood pressure.

Diuretics also widen (dilate) the blood vessels. This allows blood more space to flow through your blood vessels, which again lowers your blood pressure.

There are different types of diuretic, but the type most commonly used to treat high blood pressure is called a thiazide diuretic.

Who should take diuretics?

Thiazide diuretics are often used in people who are aged older than 55 years old and for people who are of African-Caribbean descent (but not mixed-race). This is because research has shown that this group of medicines is most effective in these groups of people.

Who should not take diuretics?

If you already have low amounts of sodium, potassium and calcium in your blood you should not take thiazide diuretics as they can also cause your body to lose these minerals. People with Addison’s disease should also not take thiazide diuretics.

If you have kidney or liver problems you will need to be carefully monitored when taking these medications and if you have severe problems you may not be able to take them at all.

If you are pregnant or breastfeeding you may need to take care when taking a thiazide diuretic called indapamide.

If you have gout or lupus you may need to take care with these medicines as they may make your condition worse.

When is the best time to take diuretics?

If you have kidney or liver problems you will need to be carefully monitored when taking these medications and if you have severe problems you may not be able to take them at all.

If you have gout or a condition called Lupus you may need to take care with these medicines as they may make your condition worse.

Women who are pregnant or breast feeding may need to take care when taking indapamide.

What are the most common side-effects of diuretics?

Thiazide diuretics can cause a fall in the levels of salts in your blood, in particular the levels of potassium. Too little potassium in your body can be dangerous, so if you are taking larger doses of thiazide diuretics you may need to have your potassium levels checked after treatment starts and annually.

Thiazide diuretics may, occasionally, cause erectile dysfunction in men, but usually only at larger doses than are now usually used.

Thiazide diuretics can rarely cause skin rashes.

If you take a thiazide diuretic with a beta-blocker you have an increased risk of developing diabetes. If you are taking this combination of medicines together, speak to your doctor at your next appointment about whether other medicines may be more appropriate for you or not.

If you develop side-effects from your medications, your doctor may be able to help by lowering your dose, or by changing your medicine. Do not stop taking any medication without first speaking to your doctor.

Type of thiazide diuretics

Most medications have two names – the generic name (which is the name of the medicine itself) and the brand name (which is the name the medicine is sold under). This means different companies may make and sell the same medicine, but they may sell it with different brand names. The table below lists some thiazide diuretic medicines currently used in the UK:

Other types of diuretics

Although thiazides are the diuretics most commonly used to treat high blood pressure, there are other types available. They include:

Loop diuretics

These medications are not commonly used to treat high blood pressure, but are mainly used when the body is holding on to fluid, such as in heart failure. Loops diuretics are more powerful, remove more fluid, and act more quickly than thiazide diuretics. They may be given to people who cannot take thiazide diuretics or who are already taking three medicines for high blood pressure.

Loop diuretics can also cause a fall in the level of salts in the blood. You may be asked to have a blood test to check for these problems. Other possible side-effects include an upset stomach and dizziness when you stand up.

Some loop diuretics used in the UK are: furosemide (brand names Furosemide, Lasix), bumetanide (brand names Bumetanide, Burinex), torasemide (brand names Torasemide, Torem).

Potassium-sparing diuretics

These are weaker kinds of diuretic and are not usually taken on their own but you can take them with a thiazide or a loop diuretic. The advantage of these diuretics is that they cause less of a fall in the level of potassium in your blood.

Potassium-sparing diuretics may be given to people who cannot take thiazide diuretics or who are already taking three medicines for high blood pressure. They may also be used to treat people who have an underlying cause for their high blood pressure, called primary hyperaldosteronism or Conn’s syndrome.

The main side-effects of this type of medicine are an upset stomach and a fall in the level of salts in the blood. Potassium-sparing diuretics should not be taken with an ACE inhibitor or an angiotensin receptor blocker as they can cause a raised potassium level in the blood which can be harmful. If you are taking a potassium-sparing diuretic, you should not take potassium supplements.

Some potassium-sparing diuretics used in the UK are: amiloride (brand names Amilamont, Amiloride, Burinex, Co-Amilofruse, Co-amilozide, Frumil, Frumil LS, Moduret 25, Moduretic) triamterene (Frusene, Co-triamterzide, Dyazide, Dytide, Kalspare), eplerenone (brand name Inspra), spironolactone (brand names Aldactone, Co-flumactone, Lasilactone, Spironolactone).