Common questions about furosemide

Furosemide is a type of medicine called a loop diuretic.

A diuretic makes your body get rid of extra fluid through your kidneys. A loop diuretic works on a specific part of the kidney called the loop of Henle to increase the salt and water you pee out.

This means you have less fluid in your tissues which helps get rid of swelling (oedema). You will also have less fluid in your blood, which helps reduce blood pressure.

Furosemide starts to work within 1 hour but it may take a few weeks to fully take effect.

If you're taking furosemide for high blood pressure, you may not have any symptoms. In this case, you may not feel any different when you take furosemide. This does not mean that the medicine is not working. It's important to keep taking it.

A dose of furosemide works for about 6 hours.

Furosemide is safe to take for a long time, but you will have to see your doctor or nurse regularly for blood and urine tests. These make sure the chemicals in your blood are properly balanced.

How often you need to see your doctor or nurse for these tests will depend on the reason you're taking furosemide, if your dose has changed recently, or if you have any other health problems.

There are other diuretics that work in a similar way to furosemide.

There are 3 different types of diuretic, and each type of diuretic works on a different part of the kidney:

• loop diuretics (such as furosemide) including bumetanide and torasemide can also be used to treat heart failure. Torasemide can also be used to treat high blood pressure
• thiazide diuretics such as bendroflumethiazide and indapamide, are used in low doses to treat high blood pressure, and in higher doses to treat heart failure
• potassium-sparing diuretics such as spironolactone and eplerenone, can be used to treat heart failure. These can also be used if you lose too much potassium with other diuretics

Even if furosemide brings down your blood pressure successfully, it’s best to carry on taking it. If you stop taking it, your blood pressure could go back up again.

If you need medicines to lower your blood pressure, you’ll probably need them for the rest of your life.

Remember, by keeping your blood pressure low, you’re protecting yourself against having a heart attack or stroke in the future.

It’s usually best to drink normally while you’re taking furosemide. A good rule is to drink enough fluid so that you’re not thirsty for long periods, and to steadily increase your fluid intake when exercising and during hot weather. Passing pale, clear pee is a good sign that you’re drinking enough.

However, if you have heart failure or kidney problems you might need to limit how much fluid you drink. Your doctor or nurse will tell you exactly how much you need to drink each day.

If you’re taking furosemide for high blood pressure or oedema you may lose a bit of weight as your body loses water. But do not take furosemide specifically to lose weight.

Only take furosemide if it’s been prescribed, and only for the reason your doctor has prescribed it for you.

Tell your doctor that you’re taking furosemide if you’re going to be put to sleep with a general anaesthetic for an operation or you’re going to have a major operation, such as a Caesarean section, without a general anaesthetic.

Furosemide can reduce your blood pressure when it’s used with a general anaesthetic.

Your doctor may advise you to stop taking furosemide 24 hours before surgery.

Furosemide will not affect any type of contraception.

However, some types of hormonal contraception, like the combined pill and contraceptive patch, are not usually recommended if you're taking furosemide. This is because some hormonal contraceptives can raise your blood pressure and stop the medicine working properly.

Talk to your doctor if you’re taking or using hormonal contraceptives.

If furosemide makes you sick (vomit), your contraceptive pills may not protect you from pregnancy. Check the pill packet to find out what to do.

Find out more:

• What to do if you're sick or have diarrhoea when taking the combined pill
• What to do if you're sick or have diarrhoea when taking the progestogen-only pill

Furosemide can make you feel confused and dizzy. If this happens to you, do not drive, cycle, or use machinery or tools until you feel back to normal.

It's an offence to drive a car if your ability to drive safely is affected. It's your responsibility to decide if it's safe to drive. If you're in any doubt, do not drive.

Talk to your doctor or pharmacist if you're unsure whether it's safe for you to drive while taking furosemide. GOV.UK has more information on the law on drugs and driving.

During the first few days of taking furosemide, it’s best to stop drinking alcohol until you see how the medicine affects you. It may lower your blood pressure and make you feel dizzy.

If you're taking a diuretic such as furosemide, it's important not to have too much salt in your food because this can stop it working.

Do not eat foods that have a lot of salt in them, such as processed foods or ready-meals. Do not add extra salt when you're cooking or at the table.

Also, do not buy salt substitutes, like Lo-Salt, instead of ordinary table salt, as they contain a lot of potassium, which can affect the way certain medicines work, or cause side effects.

Adults are advised to eat no more than 6 grams of salt a day. Your doctor will tell you if you need to eat even less than this.

You can boost your general health, plus the health of your heart, by making some key lifestyle changes. These will also help if you have high blood pressure or heart failure.

• Quit smoking – smoking increases your heart rate and blood pressure. Quitting smoking brings down your blood pressure and relieves heart failure symptoms. Try to avoid secondhand smoke too.
• Cut down on alcohol – drinking too much alcohol raises blood pressure over time and also makes heart failure worse. Men and women should not drink more than 14 units of alcohol a week.
• Be more active – regular exercise lowers blood pressure by keeping your heart and blood vessels in good condition. It does not need to be too energetic, walking every day can help.
• Eat healthily – aim to eat a diet that includes plenty of fruit and vegetables, wholegrains, fat-free or low-fat dairy products and lean proteins. It’s a good idea to follow these tips for a lower salt diet, however, it's important not to go on a low-salt diet while taking this medicine, as that could make your sodium levels too low. People need salt in their diet but eating too much salt is the biggest cause of high blood pressure. The more salt you eat, the higher your blood pressure will be. Aim for no more than 6g of salt a day.
• Manage stress – when you're anxious or upset, your heart beats faster, you breathe more heavily and your blood pressure often goes up. This can make heart failure worse too. Find ways to reduce stress in your life. To give your heart a rest, try napping or putting your feet up when possible. Spend time with friends and family to be social and help avoid stress.
• Vaccinations – if you have heart failure, it's recommended that you have the flu vaccine every year and the pneumococcal vaccine as recommended by your GP. Ask your doctor about these vaccinations. You can have them free on the NHS if you have heart failure. The coronavirus (COVID-19) vaccine is recommended for most people. Make sure you've had all the doses that you are eligible for. Talk to your doctor if you think you might be in one of the at risk groups.