Hydrochlorothiazide

Hydrochlorothiazide is a mild water tablet used to lower blood pressure. In the UK it is mostly given combined with another blood pressure medicine.

Type of medicine

Thiazide diuretic (water tablet)

Also known as

Co-amilozide (with amiloride), Co-zidocapt (with captopril)

Comes as

tablets, combination tablets

How you get it

Prescription only

What it is used for

High blood pressure, usually in a combination tablet
Fluid build-up (oedema), including in heart failure

Read our guides:

Off-label uses

Doctors sometimes prescribe a medicine for a condition it is not officially licensed for. This is called off-label use. It is legal and common when there is good evidence it helps, and your doctor should explain why they are suggesting it.

Preventing some types of kidney stone

How it works

Hydrochlorothiazide stops part of the kidney reabsorbing salt, so more salt and water leave the body in your pee. Over time it also relaxes blood vessels, which lowers blood pressure.

Side effects

Like all medicines, Hydrochlorothiazide can cause side effects, although not everyone gets them. Many are mild and ease after the first few weeks.

Common side effects

needing to pee more
feeling dizzy
headache
feeling sick
being more sensitive to sunlight

Tell your doctor or pharmacist if these bother you or do not go away.

Serious side effects

These are rare. Call 111 or contact your doctor straight away if you get:

muscle cramps, weakness, confusion or an irregular heartbeat, which can be signs of low potassium or sodium
sudden eye pain or blurred vision
a hot, swollen joint, which can be gout
a new or changing skin patch or lump

Call 999 if you have signs of a serious allergic reaction, such as swelling of your lips, mouth, throat or tongue, or trouble breathing.

You can report any side effect to the Yellow Card scheme, run by the medicines regulator.

Stopping and withdrawal

Important safety information

Long-term use is linked to a higher risk of some skin cancers. Protect your skin from the sun and check it regularly.
You need regular blood tests to check your salts.

Questions about your medicine?

A pharmacist can answer questions about your medicines for free, without an appointment. You can also ask your GP for a medication review. Check if you can get free prescriptions.