It's also sometimes used to help you pee when your kidneys aren't working properly.
Diuretics are sometimes called "water pills/tablets" because they make you pee more.
Furosemide is only available on prescription. It comes as tablets and as a liquid that you swallow. It can also be given by injection, but this is usually only done in hospital.
Furosemide sometimes comes mixed with other diuretics or potassium.
- It's usual to take furosemide once a day in the morning. Some people take it twice a day - once in the morning and again at lunchtime.
- Furosemide doesn't usually upset your tummy. You can take it whether or not you've eaten a meal or snack recently.
- The main side effect of furosemide is peeing more often than normal. Most people need to pee about 30 minutes after taking furosemide, and again within a few hours.
- Do not take furosemide after 4pm or you may have to wake in the night to go to the toilet.
- Furosemide is also called by the brand names Frusol and Lasix.
Who can and cannot take furosemide
Furosemide can be taken by most adults and children, including babies.
However, furosemide isn't suitable for everyone. To make sure furosemide is safe for you, tell your doctor if you have:
- had an allergic reaction to furosemide or any other medicine in the past
- low blood pressure
- symptoms of dehydration, such as being thirsty, having a dry mouth and dark pee
- liver disease
- difficulty peeing
- a disorder of your adrenal glands called Addison's disease
- an intolerance to, or you cannot absorb, some sugars such as lactose (in milk) or maltitol (in corn syrup)
Tell your doctor that you are taking furosemide if you're going to have:
- a glucose test
- a test (such as an X-ray or scan) that involves a dye containing iodine being injected into your blood
- a major operation or a general anaesthetic to put you to sleep
How and when to take it
When will I take it?
It's usual to take furosemide once a day in the morning.
Sometimes you take it twice a day – once in the morning and again at lunchtime. Occasionally, you take it every other day.
You don't need to take furosemide at the same time every day. You can occasionally take it at a different time if it's more convenient for you, for example if you need to go out for a few hours in the morning and you won't be near a toilet.
But do not take furosemide too late in the day (after 4pm) or at night, otherwise you may have to wake up to go to the toilet. Your doctor or pharmacist will tell you the best times for you to take your medicine.
How much will I take?
- The usual dose in adults to treat high blood pressure is 20mg to 80mg a day.
- The usual dose in adults to treat heart failure or oedema (fluid build up in the body) is 20mg to 120mg a day.
Doses are usually lower for people over 65 years as they may be more prone to side effects.
For babies and children, your doctor will use your child's weight or age to work out the right dose.
How to take it
Furosemide doesn't usually upset your tummy so you can take it whether or not you've eaten recently.
Swallow the tablets whole with a drink of water.
If you're taking furosemide as a liquid, it will come with a plastic spoon or syringe to help you measure out the correct dose. If you don't have one, ask your pharmacist for one. Do not measure the liquid with a kitchen teaspoon as it won't give the right amount.
Some people take furosemide mixed with other diuretics or potassium:
- with amiloride (also called co-amilofruse, Frumil or Frumil LS)
- with spironolactone (also called Lasilactone)
- with triamterene (also called Frusene)
- with potassium (also called Diumide-K Continus)
What if I forget to take it?
Take your forgotten dose as soon as you remember, unless it is after 4pm in the afternoon. In this case, leave out the missed dose and take your next dose at the usual time. Do not take a double dose to make up for a forgotten dose.
If you often forget doses, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicines.
What if I take too much?
Too much furosemide can cause headaches, dizziness, a pounding or irregular heartbeat and fainting. You may also pee more than normal and feel thirsty.
The amount of furosemide that can lead to an overdose varies from person to person.
Like all medicines, furosemide can cause side effects although not everyone gets them.
Side effects often get better as your body gets used to the medicine.
Common side effects
Common side effects of furosemide happen in more than 1 in 100 people. They include:
- peeing more than normal, most people need to pee a couple of times within a few hours of taking furosemide - you may also lose a bit of weight as your body loses water
- feeling thirsty with a dry mouth
- feeling confused or dizzy
- muscle cramps, or weak muscles
- feeling or being sick (nausea or vomiting)
- a fast or irregular heartbeat
Serious side effects
Some people have serious side effects after taking furosemide.
Tell your doctor straight away if you get:
- unexplained bruising or bleeding, fever, sore throat and mouth ulcers – these could be signs of a blood disorder
- severe tummy pain which could reach through to your back – this could be a sign of an inflamed pancreas (pancreatitis)
- severe pain in your side or blood in your urine – these could be signs of inflamed kidneys
- ringing in your ears (tinnitus) or loss of hearing
Serious allergic reaction
It's possible to have a serious allergic reaction (anaphylaxis) to furosemide.
These are not all the side effects of furosemide. For a full list see the leaflet inside your medicines packet.
How to cope with side effects
What to do about:
- peeing more than normal - this will last for about 6 hours after taking furosemide. It's nothing to worry about, but if it's inconvenient for you, change the time you take furosemide to one that suits you better (provided it's no later than 4pm). If peeing a lot is still a problem for you, talk to your doctor or pharmacist.
- feeling thirsty - it's important not to get dehydrated, but how much you drink will depend on why you're taking furosemide. Check with your doctor how much liquid you can drink while you're taking this medicine.
- dry mouth - chew sugar-free gum or suck sugar-free sweets.
- headaches - make sure you rest and drink fluids - ask your doctor how much you can drink while taking this medicine. Do not drink too much alcohol. Ask your pharmacist to recommend a painkiller. Talk to your doctor if the headaches last longer than a week or are severe.
- feeling confused or dizzy - if furosemide makes you feel dizzy when you stand up, try getting up very slowly or stay sitting down until you feel better. If you begin to feel dizzy, lie down so that you don't faint, then sit until you feel better. Do not drive or use tools or machines while you're feeling dizzy or shaky.
- muscle cramps or weak muscles - if you get unusual muscle pain or weakness which isn't from exercise or hard work, talk to your doctor. You may need a blood test to check what might be causing it.
- feeling or being sick (nausea or vomiting) - take furosemide with or just after a meal or snack. Take small, regular sips of water or squash so you don't get dehydrated (ask your doctor how much fluid you can drink). It may help if you stick to simple meals and don't eat rich or spicy food. This side effect usually wears off after a few days. Talk to your doctor about taking an anti-sickness medicine if it carries on for longer.
Pregnancy and breastfeeding
Furosemide is not normally recommended in pregnancy or when breastfeeding. However, your doctor may prescribe it if they think the benefits of the medicine outweigh the risks.
If you're trying to get pregnant or you're already pregnant, talk to your doctor about the benefits and possible harms of taking furosemide. These will depend on how many weeks pregnant you are and the reason you need to take it. There may be other treatments that are safer for you.
Furosemide and breastfeeding
Small amounts of furosemide may get into breast milk. It's also possible that furosemide may reduce the amount of milk you produce.
If you need to take furosemide while you're breastfeeding, your doctor and midwife will monitor your baby's weight.
Talk to your doctor, as other medicines might be better while you're breastfeeding.
Cautions with other medicines
Some medicines interfere with furosemide to stop it working properly or increase the chances of you having side effects.
Tell your doctor if you're taking:
- medicines to treat - or which have the side effect of - an irregular heartbeat, including amiodarone, digoxin, disopyramide, flecainide and sotalol
- medicines that can change the level of potassium in your blood, such as potassium supplements, steroids, or other diuretics
- medicines used to treat mental health problems, such as amisulpride, lithium, pimozide and risperidone
- painkillers known as non-steroidal anti-inflammatory drugs (NSAIDs), including diclofenac, ibuprofen and naproxen
- medicines that treat high blood pressure, or those that have a side effect of low blood pressure
- a medicine used to treat ulcers called sucralfate. Leave about 2 hours between the time you take furosemide and sucralfate.
Mixing furosemide with medicines that you buy from a pharmacy or supermarket
Some painkillers and remedies that you can buy from a pharmacy or supermarket contain a lot of sodium, which is found in salt. Too much salt can stop furosemide working properly.
Speak to a pharmacist or doctor to see if these medicines are safe for you to take alongside furosemide.
Mixing furosemide with herbal remedies and supplements
There's very little information about taking herbal remedies and supplements with furosemide.
HealthUnlocked contains information from NHS Digital, licensed under the current version of the Open Government Licence