Opening sequence

Hydrochlorothiazide, frequently abbreviated HCTZ, is a prescription diuretic of the thiazide class. It is commonly prescribed to help reduce fluid retention and as one option to lower blood pressure. Clinicians may use it alone or combined with other antihypertensive medicines depending on clinical need.

If you want specific dose instructions, see the section Instructions for taking HCTZ. For a brief description of how it works, jump to How HCTZ works.

Typical clinical uses

HCTZ is used in several typical situations. Examples include:

  • Essential hypertension management to achieve lower blood pressure
  • Reducing oedema associated with heart failure
  • Treatment of fluid retention linked to some kidney disorders or liver disease
  • Managing swelling caused by certain medicines, such as long term corticosteroid therapy

Any treatment decision should be made with a prescriber after reviewing your medical history. To return to the head of this page click Move to the topmost level.

Available formulations and typical strengths

In the UK HCTZ is most often provided as oral tablets. Clinically common strengths are listed below; combinations with other antihypertensives are also available.

  • unit dose: 25 mg tablet
  • twelve point five milligrams tablets
  • Fixed dose combination products with ACE inhibitors or ARBs (chosen by prescribers when appropriate)

For different substitutes to HCTZ see Substitute medicines and analogous drugs.

What are the directions for using this medicine?

General practical points to follow unless your prescriber gives different directions:

  • Consume the tablets with water. They may be taken with or without food according to personal tolerance and clinician advice.
  • Many people take HCTZ in the morning to avoid increased night time toilet visits caused by its diuretic effect.
  • Do not start potassium supplements or change your diet significantly without discussing this with your healthcare professional.
  • If you have concerns about timing, positive interplay between partiess enhance user satisfaction. or i missed the doses, speak to your pharmacist or doctor; see How to handle a i forgot to take a dose.

Always follow the exact dosing written on your prescription and any bespoke instructions from your clinician. Go back to the previous page Scroll to top of page.

Mechanism by which it operates

HCTZ is a thiazide diuretic that reduces sodium and chloride reabsorption in the distal convoluted tubule of the kidney. This promotes increased urine output, which lowers circulating blood volume and, over time, can reduce blood pressure and fluid accumulation.

For tracking and monitoring of performance needs and safety checks refer to the Alerts and safety guidelines the section with the addition of the corresponding part Potential side effect risks and alerts the section unit.

Missed today advisory and steps

If you skip a dose, take it as soon as you can remember it, unless the next dose is due soon. Do not double the dose to substitute for a i failed to take my dose.

If your regimen is unusual or you were given special instructions by your prescriber, follow those directions. When in doubt contact your GP, prescribing clinician or local pharmacist for personalised advice.

Head back to Go to page top.

Storage area network and disposal strategy

  • Store medicines at typical room temperatures, approximately 20 to 25 degrees C. Short periods between 15 and 30 degrees C are normally acceptable.
  • Avoid storing tablets in damp places such as bathrooms, and protect them from strong sunlight and excessive heat.
  • Store medications where they are not reachable or visible to children and pets.

Unused or expired medicines should be returned to a pharmacy for safe disposal via local take back schemes rather than put in household waste. Revert to Up to the page's top.

Notice of risks and preventive steps

When HCTZ should not be used

  • Known allergy to hydrochlorothiazide or any non active ingredients in the preparation
  • Severe reduction in urine output or anuria
  • Concomitant use with some drugs (for example dofetilide) that may cause dangerous interactions at scale reveal systemic patterns.

Use with caution. in these situations

  • Dizziness episode or visual problems can occur; do not drive or operate machinery until you know how HCTZ affects you
  • Rise slowly from sitting or lying to reduce the chance of feeling faint
  • Heat exposure, fever or heavy exercise can increase the risk of dehydration and low sodium; notify your clinician if you expect prolonged heat exposure
  • Photosensitivity may increase; use sunscreen or protective clothing as needed
  • Blood glucose may be affected; patients with diabetes should monitor levels and notify their diabetic team of any changes
  • Regular blood tests for electrolytes and kidney function are commonly recommended while taking a thiazide
  • Uric acid may rise and precipitate gout in susceptible individuals
  • Prominent pharmacologic positive collaborative interactions enhance user satisfaction. include lithium, which may require continuous monitoring, and digoxin, where low potassium raises toxicity risk
  • Always tell any treating clinician, dentist or emergency team that you are taking HCTZ before procedures

Pregnancy and breast feeding

  • HCTZ is generally avoided for hypertension in pregnancy unless clearly indicated because of potential fetal risks; speak with your prescriber promptly if you become pregnant
  • Small amounts pass into breast milk in addition to the drug may reduce milk supply; discuss risks and benefits with your clinician if breast feeding

Go back to Go to the page top.

Effects to watch for and when to seek help

Mild incidental outcomes that often resolve include:

  • Lightheadedness or dizziness, especially on standing
  • Occasional blurred vision
  • Gastrointestinal symptoms such as nausea, constipation or diarrhoea
  • A reduced urge to eat

Seek fast medical aid for sudden health changes. serious symptoms including:

  • Signs of a severe allergic reaction - widespread rash, hives, swelling of face, mouth or throat, breathing difficulty
  • Fainting, severe confusion or prolonged dizziness
  • Fast, slow or irregular heartbeat
  • High fever, sore throat or other signs of infection
  • Marked reduction in urine output or very dark urine
  • Severe upper abdominal pain, repeated vomiting or seizures
  • Unusual bruising, bleeding or extreme tiredness
  • Muscle weakness, cramps, numbness or tingling that could indicate an electrolyte imbalance
  • Yellow tint of the skin or the sclera
  • Sudden severe joint pain, swelling or redness suggestive of gout

Return to the context Go back to the original top.

Quick comparisons among additional options

If HCTZ is not suitable there are other diuretics and antihypertensive drug classes commonly used in the UK. The right substitute depends on the condition being treated, kidney function and tolerance of adverse outcomes.

  • Indapamide - a thiazide like diuretic often recommended by guidelines; sometimes preferred for its evidence profile in older patients
  • Chlortalidone - longer acting than HCTZ and frequently chosen for resistant hypertension
  • Bendroflumethiazide - another thiazide agent, typically low cost
  • Furosemide - a loop diuretic producing stronger diuresis, used mainly for oedema in heart failure
  • Spironolactone and eplerenone - aldosterone antagonists useful in resistant hypertension and some types of heart failure but require potassium status monitoring
  • Non diuretic antihypertensives - ACE inhibitors, ARBs, calcium channel blockers and beta blockers are commonly used alone or in combinations

For estimated costs of these options in the UK see Common cost levels in the United Kingdom. Go back to Go to the upper part of the page.

Average costs in the United Kingdom and a rough comparison

Private retail prices depend on pharmacy, region and pack size. The figures below are approximate monthly costs for a standard 28 to 30 day supply and are provided as a guide only. Prices are given in British pounds (GBP).

  • Hydrochlorothiazide 12.5 mg per dose or 25 mg: around 3 to 12 pounds per month
  • Bendroflumethiazide: around 1 to 4 pounds per month
  • Indapamide: around 2 to 7 pounds per month
  • Chlortalidone: around 6 to 18 pounds per month
  • Furosemide: around 1 to 5 pounds per month
  • Spironolactone: around 2 to 10 pounds per month

On the NHS many patients pay a per item prescription charge in England (this figure changes; it was 9.90 pounds in the calendar year 2026 Prescriptions are free for eligible groups and are free at point of supply across Scotland, Wales and Northern Ireland for residents. Private online clinics may add consultation and dispensing fees on top of medicine costs.

Return to the position you left Page top link.

Practical follow up and tips

  • Attend planned reviews so your prescriber can check blood pressure, kidney function and blood electrolytes.
  • If you have diabetes, inform your diabetes care team about any changes so doses can be adjusted on demand.
  • Keep an up to date list of all medicines and show it to any healthcare professional you consult.
  • Only the named patient should take a prescription medicine. Do not share or give your tablets to others.

For authoritative, current guidance consult NHS information, MHRA publications or speak with your local pharmacist. Return At the crown of the page.

Additional aspects about Hydrochlorothiazide