Chlortalidone is a 'water tablet' (a diuretic).
It is best taken in the morning, with breakfast.
Any side-effects are usually mild, but may include feeling sick (nausea) or dizziness.
|Type of medicine||A thiazide-related diuretic|
|Used for||High blood pressure; fluid retention; heart failure; diabetes insipidus|
|Also called||Chlorthalidone (in US); |
Combination brands are: Tenoret® (chlortalidone with atenolol); Tenoretic® (chlortalidone with atenolol);
Chlortalidone belongs to a group of medicines called thiazide-related diuretics. A diuretic is a medicine which increases the amount of urine that you pass out from your kidneys. They are often referred to as 'water tablets'. Diuretics are a common treatment for high blood pressure (hypertension). They are also used to clear excess fluid in some liver and kidney conditions where the body retains more fluid than it needs. Chlortalidone is also useful in people who have heart failure. Heart failure is a condition where the heart does not function as well as it should.
Diuretics like chlortalidone work by interfering with the movement of salt and water across certain cells in your kidneys. The effect of this is to make your kidneys pass out more urine. The removal of fluid reduces your blood pressure and helps reduce the work your heart has to do. Chlortalidone tends to have only a weak action on the kidneys, so it is unlikely you will notice a great increase in urine.
Chlortalidone may also be given alongside other medicines used to treat fluid retention and/or hypertension. When it is used like this, you may be prescribed a combination tablet. Combination tablets help to reduce the total number of tablets you need to take each day.
Chlortalidone tablets may also be of benefit to people with diabetes insipidus. This is a condition where a person produces large amounts of dilute urine and is constantly thirsty. How chlortalidone works in diabetes insipidus is not fully understood.
Before taking chlortalidone
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 chlortalidone it is important that your doctor knows:
- If you are pregnant or breastfeeding.
- If you have kidney or liver problems.
- If you have gout, diabetes, or an inflammatory condition called lupus or SLE (systemic lupus erythematosus). These conditions may be made worse by diuretics.
- 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 are taking or using 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.
- If you have ever had an allergic reaction to a medicine.
How to take chlortalidone
- Before you start this treatment, read the manufacturer's printed information leaflet from inside your pack. The leaflet will give you more information about the tablets and a full list of side-effects which you may experience from taking them.
- Take chlortalidone exactly as your doctor tells you to. The usual dose is ½-1 tablet daily (25-50 mg), although your dose may be different to this. Your doctor is likely to recommend that you take your dose in the morning. This is so it works during the day and your sleep is not disturbed by needing to get up to make extra trips to the toilet during the night.
- Although you can take the tablets before or after food, you are recommended to take them after a meal (usually breakfast). This is because the food in your stomach will help to reduce the side-effect of stomach upset.
- If you forget to take a dose, take it as soon as you remember. However, if it is after 6 pm in the evening, you should skip the forgotten dose and continue as usual the next day. Do not take two doses together to make up for a missed dose.
Getting the most from your treatment
- Diuretics like chlortalidone help you to lose water. Occasionally you may lose too much and become 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 chlortalidone and your doctor may want you to have a blood test from time to time to check for this.
- If you have been prescribed chlortalidone for high blood pressure, 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. It is important that you continue to take chlortalidone regularly to help reduce the risk of this.
- You may also be given some lifestyle or dietary advice by your doctor, such as stopping smoking, reducing the amount of salt in your diet and taking some regular exercise. Following this advice will help to reduce the risk of damage to your heart and blood vessels.
- Drinking alcohol while you are on chlortalidone may make you feel dizzy. Ask for your doctor's advice about whether you should avoid alcohol.
- If you buy any medicines, check with a pharmacist that they are suitable to take alongside chlortalidone.
- If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.
- If you have diabetes (diabetes mellitus), chlortalidone may affect your blood sugar (glucose) levels. Test your blood or urine regularly and speak with your doctor if you notice any significant changes.
Can chlortalidone 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 chlortalidone. 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 chlortalidone side-effects||What can I do if I experience this?|
|Loss of appetite, mild gastrointestinal effects such as feeling sick (nausea) or stomach upset||This is usually mild, but it may help to take the tablets after food|
|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 until you feel better|
|Impotence, itchy skin rash||If either of these becomes troublesome, speak with your doctor|
|Changes in some blood tests||Your doctor will monitor for this|
If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist.
How to store chlortalidone
- 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.
Further reading and references
Manufacturer's PIL, Tenoret® 50 mg/12.5 mg film coated tablets (atenolol with chlortalidone); AstraZeneca UK Ltd, The electronic Medicines Compendium. Dated December 2018.
British National Formulary, 79th Edition (Mar 2020); British Medical Association and Royal Pharmaceutical Society of Great Britain, London.