A thiazide diuretic ('water tablet')
Bendroflumethiazide
A long-established thiazide 'water tablet' used to lower blood pressure, taken once a day in the morning.
What is Bendroflumethiazide?
Bendroflumethiazide is a thiazide diuretic, often called a 'water tablet', used to treat high blood pressure. It helps the kidneys remove a little extra salt and water and relaxes blood vessels, lowering blood pressure over time. It is taken once a day in the morning so that the increase in urine does not disturb sleep.
Education and reference only. This is a plain-language guide to Bendroflumethiazide — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Bendroflumethiazide is a thiazide diuretic — a 'water tablet' — that has been used in the UK for decades to treat high blood pressure (hypertension). Although it is a diuretic, at the low intensity used for blood pressure its main benefit comes from relaxing blood vessels rather than from a large increase in urine. It is taken once a day and works gradually to bring blood pressure down and reduce the long-term risk of stroke and heart disease.
How it works
Bendroflumethiazide acts on the kidneys, reducing how much salt (sodium) and water they reabsorb, so a little more is passed out in the urine. This modestly lowers the volume of fluid in the circulation at first. Over the following weeks its main effect is thought to be a gentle relaxation and widening of small blood vessels, which is what gives the lasting fall in blood pressure. Because it changes how the kidneys handle salts, it can also alter the balance of other minerals such as potassium and sodium.
Company & origin
Originated / developed by: Introduced as a thiazide diuretic in the early 1960s.
Bendroflumethiazide (formerly called bendrofluazide in the UK) is a thiazide diuretic introduced in the early 1960s, part of the family of thiazides developed in the 1950s and 1960s. It became one of the most widely used blood-pressure medicines in the UK for many years.
What it treats
Conditions Bendroflumethiazide is used for
Practical use
How to take Bendroflumethiazide
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it once a day in the morning so the increase in urine does not disturb your sleep at night.
- Keep taking it regularly even though high blood pressure usually causes no symptoms — the benefit is in lowering long-term risk.
- Be aware it can make your skin more sensitive to sunlight, so use sun protection when needed.
- Tell your prescriber if you have gout, as it can occasionally trigger an attack, or diabetes, as it can nudge blood sugar up.
- Attend for blood tests when asked, as the medicine can change levels of salts such as sodium and potassium.
- Stand up slowly if you feel dizzy, and do not stop the tablet without advice.
Weighing it up
Advantages & disadvantages of Bendroflumethiazide
Advantages
- A long-established, inexpensive and effective blood-pressure treatment with decades of experience behind it.
- Simple once-daily morning dose.
- Works well in combination with other blood-pressure medicines and is recommended in UK guidance for many people.
Disadvantages
- Can upset the body's salt balance, lowering potassium or sodium, so blood tests are needed.
- May raise uric acid and trigger gout, and can nudge up blood sugar.
- Can increase the urge to pass urine and make the skin more sensitive to sunlight.
- Not suitable in significant kidney impairment, certain mineral problems or gout.
Practical use
Good to know
It is taken once a day in the morning so that the extra urine it produces does not interrupt sleep. Because it changes the body's salt balance, blood tests are used to check minerals such as sodium and potassium, particularly after starting or changing the dose. It can occasionally raise blood sugar or uric acid levels, the latter sometimes triggering gout, and can make the skin more sensitive to sunlight. It is taken long-term to keep blood pressure controlled.
Who should not take it / use with caution
- People with significantly reduced kidney function, certain salt imbalances (such as low sodium or potassium), or a high calcium level.
- People with gout, as it can make attacks more likely, and used with caution in diabetes because it can raise blood sugar.
- Used with caution in pregnancy and breastfeeding, where alternatives are usually preferred, and in older people who are more prone to salt imbalances.
Monitoring
- Blood pressure response
- Blood salts (sodium, potassium) and kidney function, especially after starting
- Blood sugar and uric acid where relevant
Side effects
- Passing more urine, especially early on, and feeling thirsty.
- Dizziness or light-headedness, and changes in blood salts such as low potassium or sodium picked up on blood tests.
- Less commonly raised blood sugar or uric acid (which can trigger gout), increased sensitivity to sunlight, and in men difficulty with erections.
Key interactions
- Combined with other blood-pressure medicines it lowers pressure further; care with medicines that also affect potassium.
- Anti-inflammatory painkillers (NSAIDs) can reduce its effect and stress the kidneys when combined.
- Care alongside lithium (levels can rise), digoxin, and medicines that affect heart rhythm if potassium falls.
Available as: Tablets taken once a day.
Answers
Bendroflumethiazide: frequently asked questions
Why should I take bendroflumethiazide in the morning?
It is a 'water tablet' that increases how much urine you pass for a few hours after taking it. Taking it in the morning means this happens during the day rather than at night, so it is less likely to disturb your sleep with trips to the toilet.
Why do I need blood tests on this medicine?
Bendroflumethiazide changes how the kidneys handle salts, which can lower minerals such as potassium and sodium, and can affect blood sugar and uric acid. Blood tests, especially after starting or changing the dose, check these stay in a healthy range.
Can this tablet cause gout?
It can. Thiazide diuretics may raise the level of uric acid in the blood, which can trigger a gout attack in people who are prone to it. Tell your prescriber if you have had gout, as another medicine may suit you better.
Will it make my skin more sensitive to the sun?
Sometimes. Thiazides can make the skin react more strongly to sunlight in some people, so it is sensible to use sun protection and be cautious in strong sun. Let your prescriber know if you develop an unusual rash after sun exposure.
Can I stop it once my blood pressure is normal?
A normal reading usually means the medicine is working, not that it is no longer needed. Stopping often allows blood pressure to rise again, so keep taking it as prescribed and discuss any change with your prescriber rather than stopping on your own.
The wider class
About Thiazide diuretics
Bendroflumethiazide belongs to the thiazide diuretics class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Bendroflumethiazide.
- NICE CKS: Bendroflumethiazide.
- NICE: Hypertension in adults (NG136).
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