Cardiovascular
Thiazide diuretics
e.g. indapamide, bendroflumethiazide — Mild "water tablets" used mainly for blood pressure.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Thiazide and thiazide-like diuretics are commonly used to treat high blood pressure, and occasionally mild fluid retention. They are gentler and longer-acting than loop diuretics.
How it works
They reduce sodium reabsorption in the distal tubule of the kidney, leading to modest fluid loss and, over time, relaxation of blood vessels — which is what produces the sustained blood-pressure-lowering effect.
In practice
In practice thiazide-type diuretics are used for hypertension rather than fluid overload, often as an add-on. The main thing to watch is electrolytes: they lower sodium and potassium and can raise calcium, urate and glucose. Check bloods after starting and periodically, and be alert to hyponatraemia in older people, which can present as falls or confusion.
Examples
Practical use
How to take it & use it well
- Take thiazide-type diuretics such as indapamide or bendroflumethiazide in the morning, so the extra trips to the toilet do not disturb your sleep.
- Take it at around the same time each day, with or without food.
- Keep up with any blood tests, which check your kidneys and salts such as potassium and sodium.
- If you miss a dose, take it when you remember if it is still morning; if it is late in the day, skip it rather than risk being up at night.
- Stand up slowly at first, as these medicines can cause light-headedness when you change position.
- Tell your team if you become very unwell with diarrhoea or vomiting, as fluid and salt loss can add up.
Common uses
- Hypertension (often as add-on therapy)
- Mild oedema
- Recurrent calcium kidney stones (specialist use)
Monitoring
- Electrolytes and renal function before and after starting
- Blood pressure
- Urate or glucose if relevant
Weighing it up
Advantages & disadvantages
Advantages
- They lower blood pressure and help reduce the long-term risk of stroke and heart problems.
- They are taken once a day, usually in the morning, which is simple.
- They are well established, inexpensive and widely used.
- They can also help with fluid retention in some conditions.
- They work well alongside other blood-pressure medicines as part of combined treatment.
Disadvantages
- They can lower potassium, sodium and other salts, which sometimes needs monitoring or correction.
- They make you pass more urine, which can be inconvenient, especially early in treatment.
- They can cause light-headedness, particularly when standing up.
- They may raise blood sugar and uric acid, which can trigger gout in some people.
- They are less effective if kidney function is significantly reduced.
Key safety principles
What to watch for
- Electrolyte disturbance: low sodium and potassium, raised calcium.
- Can raise urate (gout) and glucose.
- Less effective as kidney function declines — a loop diuretic may be needed instead.
Key interactions
What to avoid or check alongside
- Anti-inflammatory painkillers can reduce their blood-pressure effect and put extra strain on the kidneys.
- Combined with other blood-pressure medicines, they can cause blood pressure to drop too far, especially at first.
- Medicines and supplements that affect potassium need care, as salt levels can swing in either direction.
- Lithium levels can rise to harmful amounts with thiazides, needing close monitoring.
- Alcohol can add to the light-headedness and low blood pressure.
Patient & carer advice
- Take in the morning
- Report cramps, marked tiredness or confusion (possible low salt levels)
- Mention any history of gout
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
Thiazide diuretics: frequently asked questions
Why should I take it in the morning?
It makes you pass more urine for a few hours, so a morning dose helps you avoid needing the toilet during the night.
Do I need blood tests on this medicine?
Yes. Blood tests check your kidney function and salt levels, such as potassium and sodium, especially when you start or change the dose.
Can it affect my gout or diabetes?
It can raise uric acid, which may trigger gout in those prone to it, and it can nudge blood sugar up. Your team will monitor for this if relevant.
Why do I feel dizzy when I stand up?
Lowering blood pressure and fluid can cause light-headedness on standing. Rising slowly helps; tell your prescriber if it is troublesome.
What if I have a bug with vomiting or diarrhoea?
You can lose extra fluid and salts, so let your team know if you are very unwell, as your medicine may need pausing until you recover.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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