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Metolazone - a diuretic


Take metolazone tablets at the same time each day, preferably just after you wake up.

Either take the tablets before food or after food, but try to be consistent each day.

Treatment with metolazone may make you feel dizzy and/or tired. Do not drive and do not use tools or machines if you are affected.

Different formulations and brands of metolazone can act in a slightly different way in your body. Each time you collect a prescription, check to make sure your supply looks the same as you have had before. If not, please ask your pharmacist to check your prescription for you.

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About metolazone

Type of medicine

A sulfonamide diuretic - a 'water tablet'

Used for

High blood pressure (hypertension); fluid retention and swelling caused by heart or kidney problems

Also called


Available as


Metolazone belongs to a group of medicines called sulfonamides and is a thiazide-like diuretic. A diuretic is a medicine which increases the amount of urine that you pass out from your kidneys. They are sometimes referred to as 'water tablets'. Diuretics are a common treatment for high blood pressure (hypertension). They are also used to clear fluid from the body in conditions where your body retains too much fluid. This is called oedema.

Diuretics like metolazone work by interfering with the transport of salt and water across certain cells in your kidneys. The effect of this is to make your kidneys pass out more urine.

Metolazone can be given alongside other medicines used to treat fluid retention and/or hypertension.

Before taking metolazone

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking metolazone it is important that your doctor knows:

  • If you are pregnant, trying for a baby, or breast-feeding.

  • If you have any problems with the way your liver works, or any problems with the way your kidneys work.

  • If you have gout or diabetes. These conditions can be made worse by medicines like metolazone.

  • If you have been told by a doctor that you have low sodium or potassium levels in your blood, or high calcium levels in your blood.

  • If you have a problem with your adrenal glands, called Addison's disease.

  • If you have ever had an allergic reaction to a medicine.

  • If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.

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How to take metolazone tablets

  • Before you start this treatment, read the manufacturer's printed information leaflet from inside your pack. The manufacturer’s leaflet will give you more information about metolazone and a full list of side-effects which you may experience from taking it.

  • Take metolazone exactly as your doctor tells you to. It is usually taken once each day. Your doctor is likely to recommend that you take metolazone in the morning. This is so it works during the day and your sleep is not disturbed by you needing to get up to go to the toilet during the night.

  • The usual dose for high blood pressure is 2.5 mg to 5 mg daily. You may need to cut your tablets in half to get the correct dose. For fluid retention you will start on a dose of 2.5 mg or 5 mg, which may be increased if needed. Your doctor will advise you on this.

  • Swallow the tablet with a drink of water. It is not important whether you take your dose before or after food, but you should try to be consistent in relation to food with each dose.

  • If you forget to take a dose, take it as soon as you remember unless your next dose is nearly due. In which case take the dose that is due and leave out the forgotten one. Do not take two doses together to make up for a missed one.

Getting the most from your treatment

  • 'Water tablets' (diuretics) like metolazone help you to lose water. Occasionally you may lose too much and become lacking in fluid in the body (dehydrated). Let your doctor know if you feel constantly thirsty, your mouth is dry, or your skin looks and feels dry.

  • Try to keep your regular appointments with your doctor. This is so your doctor can check on your progress. The salt balance in your bloodstream may be upset by metolazone and your doctor may want you to have a blood test from time to time to check for this.

  • If you have been prescribed metolazone for high blood pressure (hypertension), your treatment is likely to be long-term. Although many people with high blood pressure do not feel unwell, if left untreated, high blood pressure can harm your heart and damage your blood vessels. This damage may later result in a heart attack, stroke, or kidney problems, so it is important that you continue to take the tablets regularly to help reduce the risk of this.

  • You may also be given some lifestyle and dietary advice by your doctor, such as stopping smoking, reducing the amount of salt in your diet, eating more fruit and vegetables and less saturated fat, and taking some regular exercise. Following this advice will also help to reduce the risk of damage to your heart and blood vessels.

  • Ask your doctor for advice before drinking alcohol while you are on metolazone. Alcohol will add to the blood pressure-lowering effect of metolazone which will increase the possibility of you experiencing side-effects such as dizziness.

  • If you buy any medicines, check with a pharmacist that they are suitable to take alongside metolazone.

  • If you are due to have an operation or any dental treatment, tell the person carrying out the treatment that you are taking metolazone. You may need to stop taking the medicine a few days before the procedure.

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Can metolazone tablets cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the most common ones associated with metolazone. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.

Common metolazone side-effects (these affect fewer than 1 in 10 people)

What can I do if I experience this?

Feeling sick (nausea) or being sick (vomiting), diarrhoea

Stick to simple foods. If you are not already doing so, try taking your doses after meals to see if it help. Drink plenty of water to replace any lost fluids.

Tiredness, feeling dizzy, particularly when you stand up (due to low blood pressure)

Getting up more slowly should help. Do not drive and do not use tools or machines while affected

Headache, muscle pain or muscle cramps

Drink plenty of water and ask a pharmacist to recommend a suitable painkiller


Try to eat a well-balanced diet and drink several glasses of water each day

Changes to some blood test results, including salts and sugar

Your doctor will regularly check for these

Important: On rare occasions, treatment with diuretics like metolazone has led to problems with vision including a reduced field of vision, short-sightedness and closed-angle glaucoma. If this were to happen it is usually within the first hours to weeks of starting treatment. If you notice any changes to your vision, including blurry vision or any pain in your eyes, stop taking metolazone and speak to your doctor straightaway.

If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist.

How to store metolazone

  • Keep all medicines out of the reach and sight of children.

  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Report side effects to a medicine or vaccine

If you experience side effects, you can report them online through the Yellow Card website.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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