Furosemide (Frusol, Lasix)

Furosemide is a diuretic (a water tablet).

It is best taken in the morning.

Any side-effects are usually mild, but may include feeling sick or dizzy.

Type of medicineLoop diuretic
Used forOedema (fluid retention), and high blood pressure
Also calledFrusol®; Lasix®
Brands which contain furosemide in combination with other medicines: Diumide® K Continus (furosemide with potassium); Frumil® (furosemide with amiloride); Frusene® (furosemide with triamterene); Lasilactone® (furosemide with spironolactone)
Available asTablets, oral liquid medicine and injection

Furosemide belongs to a group of medicines called loop 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. Furosemide is used to clear excess fluid from your body in conditions where your body retains more than it needs. This extra fluid causes you to feel breathless and tired, and your feet and ankles to swell. This is called oedema, and it is commonly caused by heart failure.

Diuretics are also a common treatment for hypertension (high blood pressure). Furosemide is prescribed for high blood pressure when it cannot be sufficiently controlled by other diuretics.

Furosemide can be used on its own as a diuretic, or it can be prescribed as a combination tablet alongside other diuretics such as triamterene, amiloride or spironolactone. It is sometimes prescribed as a combination tablet with a mineral called potassium.

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 furosemide it is important that your doctor knows:

  • If you are pregnant or breast-feeding.
  • If you have kidney problems, any difficulties passing urine, or if you are dehydrated.
  • If you have prostate or liver problems.
  • If you have gout or diabetes, as these conditions may be made worse by diuretics.
  • If you have been told you have low sodium or potassium levels in your blood.
  • If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
  • If you have ever had an allergic reaction to a medicine.
  • 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 furosemide and a full list of side-effects which you may experience from taking it.
  • Take furosemide exactly as your doctor has told you to. It is usual to be prescribed one dose to take each day and you will be asked to take it preferably in the morning. Your doctor will tell you how many tablets (or how much liquid medicine) to take for each dose, and this information will also be printed on the label of the pack to remind you.
  • Although furosemide is preferably taken in the morning, you can take it at a time to suit you. For example, if you want to go out in the morning and don't want to have to find a toilet, you can delay taking your dose until later. However, it is best if you take it no later than mid-afternoon. This is because you will find you need to go to the toilet a couple of times within a few hours of taking it and this will disturb your sleep if you take it too late in the day.
  • Swallow the tablet with a drink of water. You can take furosemide before or after meals.
  • If you forget to take a dose, take it as soon as you remember. However, if it is after 4 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.
  • Try to keep your regular appointments with your doctor. This is so your doctor can check on your progress. The balance of salts in your blood may be upset by furosemide. Your doctor may want you to have a blood test from time to time to check for this.
  • Diuretics like furosemide help you to lose water. Occasionally you may lose too much and become dehydrated. Let your doctor know if you feel constantly thirsty and tired, your mouth is dry, you have muscle cramps, or your skin looks and feels dry.
  • If you have been prescribed furosemide 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, so it is important that you continue to take furosemide 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 also help to reduce the risk of damage to your heart and blood vessels.
  • Drinking alcohol while you are on furosemide can 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 safe to take with your other medicines.
  • If you have diabetes, furosemide may affect your blood sugar levels. Test your blood or urine regularly and speak with your doctor if you notice any significant changes.
  • If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.

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 furosemide. 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.

Furosemide side-effectsWhat can I do if I experience this?
Feeling sick, stomach upsetThis is usually mild, but it may help to take furosemide after food
Feeling dizzy, particularly when you stand up (due to low blood pressure)Getting up and moving more slowly should help. Do not drive or use tools or machines until you feel better
Dry mouthTry chewing sugar-free gum or sucking sugar-free sweets
Blurred vision, headache, feeling tired, increased sensitivity to sunlightIf any of these become troublesome, speak with your doctor
Changes to the levels of minerals in your bodyYour doctor will ask you to have blood tests to check for this

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

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.

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.

Did you find this information useful?

Further reading & references

  • Manufacturer's PIL, Furosemide 40 mg Tablets; Accord Healthcare Limited, The electronic Medicines Compendium. Dated July 2013.
  • British National Formulary; 66th Edition (September 2013) British Medical Association and Royal Pharmaceutical Society of Great Britain, London
Original Author:
Helen Allen
Current Version:
Helen Allen
Peer Reviewer:
Dr Adrian Bonsall
Document ID:
3359 (v23)
Last Checked:
19 December 2013
Next Review:
18 December 2016
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Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.