Diuretic
A medicine that increases urine production, used to remove excess fluid.
What it means
A diuretic increases the amount of urine the kidneys produce, removing excess salt and water from the body. Commonly called water tablets.
Main types:
- Loop diuretics (furosemide) — strong and fast-acting, for fluid overload in heart failure
- Thiazides (indapamide, bendroflumethiazide) — milder, used for blood pressure
- Potassium-sparing (spironolactone) — retain potassium rather than losing it
In practice
Diuretics affect kidney function and blood salts, so kidney function and electrolytes are checked before starting and periodically afterwards.
Timing matters practically: taken in the morning rather than the evening, to avoid being woken repeatedly.
Why it matters
During vomiting, diarrhoea or heat illness, diuretics can cause dangerous dehydration and kidney injury. Sick day rules apply — diuretics are among the medicines to pause temporarily when acutely unwell and unable to keep fluids down, and restarted once eating and drinking normally.
Diuretics should not be used for cosmetic fluid loss or weight loss. The weight lost is water, and the risks are real.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026