Losartan is a medicine widely used to treat high blood pressure and to protect your kidneys if you have kidney disease with diabetes.

Losartan helps to prevent future strokes, heart attacks and kidney problems. It also improves your survival if you’re taking it for heart failure or after a heart attack.

This medicine is only available on prescription. It comes as tablets.

  • Losartan lowers your blood pressure and makes it easier for your heart to pump blood around your body.
  • It’s often used as a second-choice treatment if you had to stop taking another blood pressure-lowering medicine because it gave you a
    dry, irritating cough.
  • If you get severe vomiting or diarrhoea from a stomach bug or illness while taking losartan, tell your doctor. You may need to stop taking it until you feel better.
  • The main side effects of losartan are dizziness and fatigue – but they’re usually mild and short-lived.
  • Losartan is not normally recommended in pregnancy and while breastfeeding. Talk to your doctor if you’re trying to get pregnant, you’re already pregnant or you’re breastfeeding.
  • Losartan is also called by the brand name Cozaar.

Losartan can be taken by adults aged 18 years and over.

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 in the past, but had to stop taking them because of side effects such as a dry, irritating cough.

Losartan isn’t suitable for some people.

To make sure losartan is safe for you, tell your doctor if you:

  • have had an allergic reaction to losartan or other medicines in the past
  • have diabetes
  • have heart, liver or kidney problems
  • recently had a kidney transplant
  • diarrhoea or vomiting (or if you’ve recently had it)
  • have been on a low salt diet
  • low blood pressure
  • are trying to get pregnant, are already pregnant or you are breastfeeding

Take losartan tablets once a day.

Your doctor may suggest that you take your first dose before bedtime, because it can make you dizzy. After the very first dose, you can take losartan at any time of day. Try to take it at the same time every day.

You can take losartan tablets with or without food. Swallow the tablets with a drink of water.

How much will I take?

The dose of losartan you take depends on why you need the medicine. Take it as instructed by your doctor.

Usually, adults take:

  • 50mg to 100mg once a day to treat high blood pressure and to protect their kidneys
  • 12.5mg to 150mg once a day for heart failure

The dose may be lower if you’ve recently lost body fluids (for example, because of diarrhoea or vomiting) or you’re over the age of 75.

If your child needs losartan, your doctor will usually use your child’s weight to work out the right dose.

Will my dose go up or down?

After a few weeks your doctor will check your blood pressure and ask you if you’re getting any side effects. You may also have 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 doesn’t get your blood pressure down, your doctor may want to increase the dose. If your blood pressure gets too low or you get side effects, your doctor may want to lower your dose.

Like all medicines, losartan can cause side effects although not everyone gets them. Side effects often improve as your body gets used to the medicine.

Common side effects

These common side effects happen in more than 1 in 100 people:

  • feeling dizzy or having a spinning sensation (vertigo)
  • headaches
  • feeling sick
  • vomiting or diarrhoea
  • pain in your joints or muscles

Talk to your doctor or pharmacist if these side effects bother you or don’t go away.

Serious side effects

It happens rarely, but some people have serious side effects after taking losartan.

Tell a doctor straight away if you have:

  • yellow skin or eyes – this can be a sign of liver problems
  • severe stomach pain – this can be a sign of an inflamed pancreas
  • pale skin, feeling tired, faint or dizzy, purple spots, any sign of bleeding, sore throat and fever – these can be signs of blood or bone marrow disorder
  • weakness, an irregular heartbeat, pins and needles and muscle cramps – these can be signs of changes in the sodium and potassium levels in your blood

Serious allergic reaction

In rare cases, losartan may cause a serious allergic reaction (anaphylaxis).

What to do about:

  • feeling dizzy – if losartan 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. Don’t drive or use tools or machines if you feel dizzy, have muscle cramps or muscle pain, or if you just feel a bit shaky.
  • headaches – make sure you rest and drink plenty of fluids. Don’t drink too much alcohol. Ask your pharmacist to recommend a painkiller. Headaches should usually go away after the first week of taking losartan. Talk to your doctor if they last longer than a week or are severe.
  • feeling sick – try taking your tablets with or after a meal or snack. It may also help if you don’t eat rich or spicy food.
  • vomiting or diarrhoea – drink plenty of water to prevent dehydration. If you’re vomiting try small, frequent sips. It may also help to take oral rehydration solutions to prevent dehydration. You can buy these from a pharmacy or supermarket. If you get severe vomiting or diarrhoea from a stomach bug or illness, tell your doctor. You may need to stop taking losartan for a while until you feel better.
  • pain in your joints or muscles – if you get unusual muscle pain, weakness or tiredness 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.

Losartan 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 losartan. These will depend on how many weeks pregnant you are and the reason you need to take it. There may be other treatments that areb safer for you.

Losartan and breastfeeding

Small amounts of losartan may get into breast milk. This can cause low blood pressure in the baby. Talk to your doctor, as other medicines might be better while you are breastfeeding.

Some medicines interfere with 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 (if you are taking more than 3g a day)
  • potassium supplements or salt substitutes which contain potassium
  • heparin (a blood thinning medicine)
  • water tablets (diuretics)
  • lithium (a medicine for mental health problems)
  • spironolactone (a medicine to treat heart failure)

Mixing losartan with herbal remedies or supplements

There’s very little information about taking herbal remedies and supplements with losartan.

How does losartan work?