Losartan is a medicine called angiotensin receptor blocker (ARB). It's widely used to treat high blood pressure (hypertension) and heart failure. It's also used to protect your kidneys if you have both kidney disease and diabetes (diabetic kidney disease).
Losartan can also help to prevent strokes and heart attacks, and is used to improve your survival if you're taking it for heart failure or after a heart attack.
Like other ARBs, losartan relaxes and widens your blood vessels. This lowers your blood pressure and makes it easier for your heart to pump blood around your body.
Losartan can also be combined with hydrochlorothizide and is called by the brand name Cozaar-Comp.
This medicine is only available on prescription. It comes as tablets.
Who can take losartan
Most adults aged 18 years and over can take losartan.
Children aged 6 years and older can take it, but only to treat high blood pressure.
Your doctor may prescribe losartan if you've tried taking similar blood pressure-lowering medicines such as ramipril and lisinopril, but had to stop because of side effects such as a dry, irritating cough.
Who may not be able to take it
Losartan is not suitable for some people. To make sure it's safe for you, tell your doctor if you:
- have ever had an allergic reaction to losartan or any other medicine
- have diabetes
- have heart, liver or kidney problems
- recently had a kidney transplant
- have had diarrhoea or vomiting while taking losartan
- have been on a low salt diet
- have low blood pressure (hypotension)
- are trying to get pregnant, are already pregnant or you are breastfeeding
Dosage and strength
Your dose of losartan depends on why you need the medicine.
Losartan comes as 12.5mg, 25mg, 50mg and 100mg tablets.
The usual dose for adults is:
- 50mg to 100mg, taken once a day to treat high blood pressure or protect your kidneys
- 12.5mg to 150mg, taken once a day for heart failure
- 25mg, taken once a day by over 75s to protect kidneys
The dose may be lower if you've recently had diarrhoea or been sick (vomiting), or you are over the age of 75.
If your child needs losartan, their doctor will usually use your child's weight to work out the right dose.
Changes to your dose
After a few weeks your doctor will check your blood pressure and ask if you're getting any side effects. You may also need blood tests to check how well your kidneys are working and the amount of potassium in your blood. Your doctor will then decide whether to change your dose of losartan.
If losartan does not bring your blood pressure down, your doctor may want to increase your dose. If your blood pressure gets too low or you get side effects, your doctor may lower your dose.
Take losartan even if you feel well, as you will still be getting the benefits of the medicine.
Take losartan tablets once a day.
Your doctor may suggest that you take your first dose before bedtime, because it can make you feel dizzy. After your first dose, you can take losartan at any time of day. But try to take it at the same time every day.
You can take losartan tablets with or without food. Swallow the tablet whole with a drink of water.
How long to take it for
Usually, treatment with losartan is long term, and you may have to take it for the rest of your life.
If you get sick while taking it
If you have severe diarrhoea or are being sick (vomiting) for any reason, contact your doctor or a pharmacist. They'll be able to advise you about what to do. They may recommend that you stop taking losartan until you're better, and you can eat and drink normally again.
If you take contraceptive pills and you're being sick or have severe diarrhoea, your contraception may not protect you from pregnancy. Check the pill packet for advice.
If you forget to take it
If you miss a dose of losartan, take it as soon as you remember. If you do not remember until the next day, leave out the missed dose and carry on as normal.
Do not take 2 doses to make up for a forgotten one.
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 medicine.
Stopping losartan may cause your blood pressure to rise, and this can increase your chances of having a heart attack or stroke.
If you're bothered by side effects, your doctor may be able to prescribe you a different blood pressure-lowering medicine.
If you take too much
The amount of losartan that can lead to an overdose varies from person to person.
An overdose of losartan can cause dizziness, sleepiness and a pounding heartbeat (palpitations).
- you take more than your prescribed dose of losartan
Go to 111.nhs.uk or call 111
If you need to go to A&E, do not drive yourself. Get someone else to drive you or call for an ambulance.
Take the losartan packet or leaflet inside it plus any remaining medicine with you.
Common side effects
These common side effects of losartan happen in more than 1 in 100 people. There are things you can do to help cope with them:
Speak to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or lasts more than a few days.
Serious side effects
It happens rarely, but some people have serious side effects after taking losartan.
Call a doctor or contact 111 straight away if:
- the whites of your eyes turn yellow, or your skin turns yellow although this may be less obvious on brown or black skin – this can be a sign of liver problems
- you get severe stomach pain – this can be a sign of an inflamed pancreas
- your skin becomes more pale than usual, you feel tired, faint or dizzy, get purple spots (that come from superficial bleeding into the skin), show any sign of bleeding, or have a sore throat and high temperature – these can be signs of a blood or bone marrow disorder
- you feel weak, have an irregular heartbeat, pins and needles and muscle cramps – these can be signs of changes in the potassium levels in your blood
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to losartan.
Sometimes, taking losartan for a long time can cause your kidneys not to work as well as they should. Your doctor will check how well your kidneys are working with regular blood tests.
Other side effects
These are not all the side effects of losartan. For a full list, see the leaflet inside your medicine packet.
Losartan and pregnancy
Losartan is not recommended in pregnancy. It can reduce the level of fluid around your baby, particularly if you take it in the second and third trimesters of pregnancy. This can result in long-term damage to your baby's kidneys and lungs and a number of other problems.
If you're already pregnant, stop taking losartan and talk to your doctor straight away. Usually, your doctor will be able to prescribe a different medicine that is safer to take in pregnancy. Losartan should always be stopped by the time you're 12 weeks pregnant.
Use contraception if you're taking losartan and carefully plan any pregnancy with your doctor, obstetrician or hospital specialist. They will review your medical condition and medicine before you get pregnant.
Most women come off losartan before getting pregnant, but some may continue up until they have a positive pregnancy test and then stop. Your doctor will discuss what's best for you, based on your medical condition and the risks and benefits of losartan.
Losartan and breastfeeding
It might be OK to take losartan while breastfeeding, but talk to your doctor or pharmacist first. It is best not to take losartan if your baby was born prematurely, but your doctor will help you decide.
It is not known how much losartan gets into breast milk, but it's likely to be a small amount. However, there is a very small risk that it could also lower your baby's blood pressure. Until we know more about losartan in breastfeeding, your doctor might recommend a different medicine for you to take.
If you notice that your baby is not feeding as well as usual, seems unusually sleepy, looks much paler than normal, or if you have any other concerns about your baby, talk to your health visitor, midwife or doctor as soon as possible.
Losartan and fertility
There's no evidence to suggest that taking losartan reduces fertility in either men or women.
However, if you're trying to get pregnant, talk to your doctor first as they may wish to switch you to a different medicine that can be taken in pregnancy.
Cautions with other medicines
Some medicines can affect the way losartan works.
Tell your doctor if you're taking:
- other medicines to help lower your blood pressure, including aliskiren, enalapril, captopril, lisinopril or ramipril
- painkillers such as ibuprofen, naproxen, diclofenac, celecoxib or etoricoxib
- aspirin more than 3g a day
- heparin, a medicine to help prevent blood clots
- tablets to make you pee more (diuretics)
- lithium, a medicine for mental health conditions
- spironolactone, a medicine to treat heart failure
Mixing losartan with herbal remedies and supplements
Tell your pharmacist or doctor if you're taking potassium supplements or salt substitutes which contain potassium.
There's not enough information to say that other herbal remedies and supplements are safe to take with losartan. They're not tested in the same way as pharmacy and prescription medicines. They're generally not tested for the effect they have on other medicines.
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