Bendroflumethiazide: blood pressure and fluid tablet explained

Bendroflumethiazide is prescribed for high blood pressure and for oedema, the swelling that comes from excess fluid. As a thiazide diuretic it helps the body remove surplus water and salt, which reduces the volume of blood being pushed round the arteries and lowers pressure over days.

The two uses get different dosing. The NHS gives 2.5mg once a day as the usual adult dose for blood pressure, while for fluid build-up the usual dose is 5mg to 10mg once a day, though it can be reduced to a single dose taken one to three times a week. Older people and those with kidney problems are often started lower.

Take it in the morning. The NHS explains that a later dose can mean waking at night to pass urine. If your prescriber has split the dose in two, the second is around midday. Where the schedule is two or three days a week, take it on the same days each week.

You may take bendroflumethiazide with or without food. For high blood pressure the treatment is often indefinite, so it helps to attach the tablet to a regular morning habit and to keep a repeat prescription going.

Most adults and children, including babies, can take it, but the NHS lists a number of conditions that make it unsuitable or call for care. These include allergic reactions to it or other medicines, Addison's disease, low blood levels of sodium, potassium or magnesium, high calcium or uric acid levels, liver problems, kidney problems or difficulty passing urine, active vomiting or diarrhoea, diabetes, gout and lupus.

Being pregnant, trying for a baby or breastfeeding also matters, covered below. If any of these apply, the prescriber may suggest a different medicine or arrange more frequent tests.

The list of common effects includes needing to pee more, thirst with a dry mouth, nausea or vomiting, diarrhoea, loss of appetite, constipation, severe joint pain that may be gout, and dizziness or faintness. Many settle as the body adjusts.

Contact NHS 111 or your doctor for unexplained bruising, bleeding, sore throat or repeated infections, severe tummy pain with fever and sickness, yellow skin or eyes with dark urine or pale stools, intense itching, or unusual tiredness with reduced urine. Call 999 for signs of a serious allergic reaction such as swelling of the lips, mouth or throat or difficulty breathing. Avoid driving if you feel dizzy or faint, and report suspected side effects through the Yellow Card scheme.

Alcohol can lower blood pressure further or cause dehydration and dizziness. The NHS suggests waiting a few days after starting before drinking so you can see how you react, and keeping within the 14 units a week guideline; people with high blood pressure should avoid regular large amounts.

It is not normally used in pregnancy as other medicines are more suitable. If you are breastfeeding it may be used when the baby is healthy, though alternatives might be preferred, and long courses or high doses could reduce milk supply. There is no evidence it reduces fertility, although it may rarely cause erectile dysfunction that usually clears after stopping.

Expect regular appointments to check blood pressure and blood tests for kidney function and salt balance. If you stop, blood pressure is likely to rise again and fluid may return, and the NHS notes a blood test after one to two weeks may be suggested to check salt levels after changes.

Missed a dose? Take it when remembered unless it is late afternoon for a morning tablet, then skip it. Never double up. An overdose can cause vomiting, dizziness and dehydration, so contact NHS 111 for advice.