General Medicine
High Blood Pressure (Hypertension)
Blood pressure that stays above 140/90 damages the heart, brain and kidneys silently. What the numbers mean, and what actually brings them down.
19 Aug 202612 min read
Diuretic
Pronounced dy-yoo-RET-ik
Also known as Water tablet, Water pill
A diuretic is a medicine that makes the kidneys pass more salt and water into the urine, lowering blood pressure and clearing fluid that has built up in the legs or the lungs. They are commonly called water tablets.
The kidneys filter blood and then reabsorb most of the salt and water back. A diuretic blocks part of that reabsorption, so more leaves in the urine and the volume circulating falls. Less volume means lower pressure in the arteries, and less fluid available to leak into tissue — which is why the same class of medicine treats both and the swelling of heart failure.
The main groups
| Group | Examples | Mainly used for |
|---|---|---|
| Thiazide and thiazide-like | Hydrochlorothiazide, indapamide, chlortalidone | Long-term blood pressure control |
| Loop | Furosemide, torasemide | Clearing in heart, liver or kidney failure; stronger and faster |
| Potassium-sparing | Spironolactone, amiloride | Heart failure, resistant hypertension, and protecting potassium alongside another diuretic |
Practical points that make them easier to live with. Take the dose in the morning, and a second dose no later than mid-afternoon, so the night is not spent going to the bathroom. Expect to pass more urine for the first week or two. Weigh yourself at the same time each morning if you are taking one for heart failure — a gain of two kilograms over two or three days means fluid is returning and needs reporting before breathlessness starts.
The important risks all follow from what the medicine does. It removes salts along with water, so potassium and sodium are checked after starting and periodically thereafter; low potassium causes cramps, weakness and can provoke an , while spironolactone can push potassium too high instead. It can also raise and cause light-headedness on standing. In , a stomach upset or a heatwave, a diuretic can tip someone into kidney injury, and it is often paused for a day or two on medical advice.
Where this comes up
Related terms
- OedemaEdema, Fluid retentionOedema is swelling caused by fluid collecting in the tissues, most often seen in the ankles and legs. It is a sign rather than a diagnosis, and what matters is the reason behind it.
- Blood pressureBP, Arterial pressureBlood pressure is the force of blood against the artery walls, written as two numbers in millimetres of mercury: the higher one is the pressure as the heart squeezes, the lower one the pressure as it refills. It varies through the day, so a diagnosis is never made on one reading.
- ElectrolyteSerum electrolytes, SaltsElectrolytes are the dissolved salts in blood and body fluid — sodium, potassium, chloride, bicarbonate, calcium and magnesium — that carry the electrical charges nerves and muscles depend on. Even small departures from the normal range can cause serious symptoms.
- RenalKidney, NephricRenal simply means relating to the kidneys. It appears throughout medical language — renal function, renal failure, renal stones — where the everyday word would be kidney.