Diuretics are medications that are prescribed to treat high blood pressure. They are sometimes referred to as ‘water tablets’, because they can cause you to pass more urine than you would typically.

  1. Treats high blood pressure.
  2. Are often prescribed when calcium blockers prove ineffective.
  3. Help prevent serious health events, such as heart attacks and strokes.

If you have any concerns about symptoms relating to the conditions mentioned above, you can speak with one of our GMC-registered clinicians via our online video consultation service. Our clinicians are available for appointments between 9.30am-4.30pm, Monday to Friday. 

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What are diuretics?

Diuretics are drugs that help the body eliminate excess water from the body and are therefore sometimes referred to as water tablets. They are most commonly prescribed to treat high blood pressure, eliminating water and salt from the body and allowing blood to be pumped around the body more freely.

What is high blood pressure? 

High blood pressure, also referred to as hypertension, is a very common condition in the UK, with as many as one third of adults believed to have it. Because it presents with no symptoms, it often goes undiagnosed for long periods of time. High blood pressure itself does not present any health risks, but it can lead to very serious health consequences, such as heart attacks, strokes, kidney disease, vascular dementia, peripheral arterial disease, heart failure and aortic aneurysms.

You can get your blood pressure checked at your local GP surgery; it involves a simple, non-invasive test. Blood pressure checks can also be carried out at pharmacies, and even in some workplaces. Blood pressure is measured by two numbers; the higher number is systolic pressure (the force at which blood is pumped) and the lower number is diastolic pressure (the resistance that force faces in the blood vessels). High blood pressure is diagnosed when these numbers reach beyond 140/90mmHg (150/90mmHg if you are over the age of 80).

What causes high blood pressure?

The precise causes of high blood pressure are not clearly defined, but there are thought to be some significant risk factors at play. These include being of African or Caribbean heritage, ageing, having a family history of the condition, smoking, alcohol consumption, poor sleep, lack of exercise, having too much salt in your diet and obesity. 

Some medications can also significantly increase your blood pressure, including cough medications, the contraceptive pill, steroids, non-steroidal anti-inflammatory drugs (NSAIDs), serotonin and norepinephrine reuptake inhibitors (SNRIs), amphetamines and herbal supplements that contain liquorice.

How is high blood pressure treated?

High blood pressure can often be effectively treated by making simple lifestyle changes, which reduces the need for medications. These include quitting smoking, lowering your salt intake, maintaining a healthy diet, cutting down on your alcohol consumption, reducing your caffeine intake, getting regular exercise and losing weight. Should these practices prove ineffective, or if your risks are thought to be too high, medications may then be offered.

For people under the age of 55, ACE inhibitors are typically the first line of treatment. ACE inhibitors work by relaxing your blood vessels and allowing blood to flow more freely. If this treatment is not suitable for you, angiotensin-2 receptor blockers (ARBs) may be suggested. 

If you are over the age of 55, or from an African or Caribbean background, calcium channel blockers are likely to be prescribed. Calcium channel blockers widen the blood vessels, and have the same functionality as ACE inhibitors and ARBs.  Diuretics are often prescribed in combination with calcium channel blockers. They work by helping the body to flush out fluid and salt in the bloodstream, which can put more strain on the heart. Beta blockers may be prescribed if these other treatments have proven to be ineffective. They help to reduce the heart rate, which in turn reduces blood pressure. 

If you would like to discuss diuretics or any related conditions or treatments with a GPhC-registered clinician, you can use our online video consultation service, from 9.30am-4.30pm, five days a week. Our clinicians can also issue referrals to specialists for treatments and fit notes, where appropriate. 

Page last reviewed:  03/07/2020
Types of Treatment

What side effects can diuretics cause?

As is the case with any medication, diuretics can cause side effects, so it is important that you fully understand what these are before starting treatment. Your prescribing clinician can discuss any potential side effects with you, and a full list of possible side effects can be found on the patient information leaflet that comes with your medication. 

Because there are different types of diuretics, side effects may differ from treatment to treatment. The following information relates to bendroflumethiazide, and you should stop using it if you experience: rashes, sensitivity to light, a viral infection, fluid in the lungs, blood cell level changes, bruising, nosebleeds, sore throats, infections, excessive tiredness, breathlessness and paleness.

The following side effects have been reported for bendroflumethiazide, but there is not enough data to suggest their frequency: affected level of sugar in the blood, gout, low potassium levels causing an increase in urination, general discomfort and illness, muscle weakness, cramps, dizziness, nausea, vomiting, loss of appetite, low magnesium, low sodium, high levels of calcium, low levels of chloride ions, diarrhoea, constipation, stomach irritation, inflammation of the pancreas, blocked bile flow (presenting as jaundice – yellowing of the skin or whites of the eyes, dark urine and pale stools), erectile dysfunction and dizziness when standing.

Is it safe to take diuretics alongside other treatments?

All medications can interact with other treatments, so it is essential that you inform your doctor about any treatments or supplements you are, or have recently, taken. 

In the case of bendroflumethiazide, it is particularly important that you make your doctor aware of any use of the following medications: Allopurinol, colestyramine, colestipol, disopyramide, amiodarone, flecainide, quinidine, lidocaine, mexiletine, tricyclic antidepressants, reboxetine, monoamine-oxidase inhibitors (MAOIs), sulfonylureas, carbamazepine, amphotericin, prazosin, ACE inhibitors, angiotensin-II antagonists, pimozide, thioridazine, calcium salts, calcium channel blockers, moxisylyte, corticosteroids, cisplatin, digoxin, aminoglutethimide, toremifene, lithium, muscle relaxant, tizanidine, tubocurarine, gallamine, alcuronium, pancuronium, NSAIDs (non-steroidal anti-inflammatory drugs), ketorolac, ibuprofen, piroxicam, naproxen, oestrogens, combined oral contraceptives, sympathomimetics, theophylline, carbenoxolone and vitamin D. 

Warnings and precautions when using diuretics

If you have any conditions that you are currently experiencing or are prone to, your prescribing clinician will need to know about these before you start taking diuretics. In the case of bendroflumethiazide, it is unsuitable if you have: allergies to any of its ingredients, severely impaired kidney or liver function, high blood levels of calcium, low blood levels of sodium, low blood levels of potassium, gout and Addison’s disease. 

Your prescribing clinician may also deem bendroflumethiazide to be unsuitable for you if you have: mild or moderate impaired kidney or liver function, liver disease, diabetes and systemic lupus erythematosus (SLE).

If you are due to have any blood tests whilst taking this medication, it is important that your prescribing doctor is made aware of this, as it may affect the blood test results.

Long term use of this medication, particularly in the elderly, may require frequent tests to monitor kidney function.

What types of diuretics are available? 

Diuretics fall into three categories, each with their own advantages and disadvantages. These are oral thiazides, loop diuretics and potassium-sparing diuretics. Each type targets one part of the kidneys. 

Oral thiazides include: Chlorothiazide, metolazone, hydrochlorothiazide, bendroflumethiazide chlorthalidone and indapaminde. 

Loop diuretics include: Furosemide, ethacrynic, bumetide and torsemide.

Potassium-sparing diuretics include: Eplerenone, triamterene and spironolactone.

Are diuretics safe to use if you are pregnant?

Diuretics should not be used whilst you are pregnant or breastfeeding. If you are pregnant, think you may be pregnant, are planning on becoming pregnant or are breastfeeding, you should inform your prescribing clinician before starting treatment.

Page last reviewed:  03/07/2020
Questions and Answers

Can diuretics cause an allergic reaction?  

All medications carry some risks of causing an allergic reaction, so it’s important that you inform your prescribing doctor of any allergies that you have before starting treatment. Certain diuretic tablets contain lactose, so if you are intolerant, you should discuss this with your doctor.

Can diuretics affect my ability to drive?

Diuretics can cause drowsiness. If you are unsure, you should wait to see how your medication affects you before driving, and speak to your prescribing clinician. 

Can I buy them over the counter? 

No. Diuretics are a prescription-only treatment. 

How can I buy diuretics online?

Our registered clinicians can discuss diuretics or any related conditions with you via our online video consultation service. You can book an appointment to speak to one of them between 9.30am and 4.30pm, Monday to Friday. They can also issue fit notes and referral to specialists for treatment, where suitable. 

Page last reviewed:  03/07/2020

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