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  1. About olmesartan
  2. Key facts
  3. Who can and cannot take olmesartan
  4. How and when to take it
  5. Side effects
  6. How to cope with side effects
  7. Pregnancy and breastfeeding
  8. Cautions with other medicines
  9. Common questions

1. About olmesartan

Olmesartan is a medicine used to treat high blood pressure.

Olmesartan helps prevent future strokes, heart attacks and kidney problems.

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

NHS coronavirus advice

If you have coronavirus, or think you might have it, keep taking your blood pressure medicines as usual.

There is no clear evidence that taking angiotensin receptor blockers (ARBs) like olmesartan will cause complications.

Updated: 17 March 2020

2. Key facts

  • Olmesartan lowers your blood pressure and makes it easier for your heart to pump blood around your body.
  • It's often used as an alternative treatment if you have had to stop taking a similar medicine because it gave you a dry, irritating cough.
  • The main side effects of olmesartan are dizziness, headaches and flu-like symptoms, but they're usually mild and short-lived.
  • If you're being sick (vomiting) or have severe diarrhoea because of a stomach bug or illness while taking olmesartan, tell your doctor. You may need to stop taking it until you feel better.
  • Olmesartan isn't normally recommended in pregnancy or while breastfeeding. Talk to your doctor if you're trying to get pregnant, are already pregnant or you're breastfeeding.
  • Olmesartan is also called by the brand name Olmetec.

3. Who can and cannot take olmesartan

Olmesartan can be taken by adults, and by children aged 6 years and over.

Your doctor may prescribe olmesartan if you have tried taking blood pressure-lowering medicines called angiotensin converting enzyme (ACE) inhibitors, such as ramipril and lisinopril, but had to stop taking them because of side effects such as a dry cough.

Olmesartan isn't suitable for some people.

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

  • have had an allergic reaction to olmesartan or any other medicines in the past
  • have problems with your bile ducts or gallbladder, such as blocked bile ducts or gallstones
  • have diabetes
  • have heart, liver or kidney problems, or have recently had a kidney transplant
  • have severe diarrhoea or vomiting or have recently had this
  • are on (or have recently been on) a low-salt diet
  • have low blood pressure
  • are trying to get pregnant, are already pregnant or you're breastfeeding

4. How and when to take it

Take olmesartan tablets once a day.

Your doctor may suggest that you take your first dose before bedtime, as it can make you dizzy.

After the very first dose you can take olmesartan at any time of day.

Usually people take olmesartan in the morning, but it doesn't really matter. Just try to take it at the same time every day.

You can take olmesartan tablets with or without food.

Swallow the tablets whole with a drink of water. Do not crush or chew the tablets.

Speak to a pharmacist if you or your child have difficulty swallowing tablets.


Always take olmesartan as instructed by your doctor.

For adults and children aged 6 years and over, the usual dose is 10mg taken once a day to start with.

Your dose may eventually go up to 20mg or 40mg, taken once a day.

Children weighing less than 35kg (about 5.5 stone) should not take more than 20mg daily.

Your child's doctor will calculate the right dose based on how much they weigh.

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 olmesartan.

If olmesartan does not bring 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.


Take olmesartan even if you feel well, as you'll still be getting the benefits of the medicine.

What if I get sick while I'm taking it?

If you get severe diarrhoea or 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 olmesartan until you're better and able to eat and drink normally again.

What if I forget to take it?

If you miss a dose of olmesartan, take it as soon as you remember if it's on the same day.

If you don't remember until the next day, skip the forgotten dose and take your next dose at the usual time.

Do not take a double dose to make up for a forgotten one.

If you forget doses often, 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.

What if I take too much?

An overdose of olmesartan can cause low blood pressure and dizziness.

The amount of olmesartan that can lead to an overdose varies from person to person.

Urgent advice: Call your doctor or go to A&E now if:

  • you take too many olmesartan tablets

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 olmesartan packet or leaflet inside it, plus any remaining medicine, with you.

5. Side effects

Like all medicines, olmesartan 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
  • headache or flu-like symptoms, or pain in your back, bones or joints
  • feeling sick (nausea), stomach ache or indigestion
  • diarrhoea
  • swollen feet, ankles or legs
  • urinary tract infection (UTI)

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 olmesartan.

Call a doctor straight away if you have:

  • blood in your pee
  • itching, a rash or lumps on your skin, or tiny red spots under the skin
  • severe diarrhoea that doesn't go away and causes noticeable weight loss
  • cuts that won't stop bleeding, unexplained bruising, bleeding gums, nosebleeds or unusually heavy periods
  • weak muscles, numbness or tingling, an irregular heartbeat or palpitations, and feeling sick and short of breath - these can be signs of high levels of potassium in your blood

Serious allergic reaction

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

Immediate action required: Call 999 or go to A&E now if:
  • you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
  • you're wheezing
  • you get tightness in the chest or throat
  • you have trouble breathing or talking
  • your mouth, face, lips, tongue or throat start swelling

You could be having a serious allergic reaction and may need immediate treatment in hospital.

These are not all the side effects of olmesartan. For a full list, see the leaflet inside your medicines packet.


You can report any suspected side effect using the Yellow Card safety scheme.

Visit Yellow Card for further information.

6. How to cope with side effects

What to do about:

  • feeling dizzy – if olmesartan 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 you do not faint, then sit until you feel better. Do not drive or use tools or machines if you feel dizzy.
  • headache or flu-like symptoms, or pain in your back, bones or joints – make sure you rest and drink plenty of fluids. Take paracetamol if you need to, or ask your pharmacist to recommend a painkiller. Talk to your doctor if these side effects last longer than a week or are severe.
  • feeling sick (nausea), stomach ache or indigestion – try taking your tablets with or after a meal or snack. It may also help if you do not eat rich or spicy food. Talk to a pharmacist before taking indigestion remedies like antacids, as some of them can stop olmesartan working properly.
  • diarrhoea – drink plenty of water to prevent dehydration. Speak to a pharmacist if you have signs of dehydration, such as peeing less than usual or having dark, strong-smelling pee. If you get severe diarrhoea or vomiting from a stomach bug or illness, tell your doctor. You may need to stop taking olmesartan for a while until you feel better.
  • swollen feet, ankles or legs – raise your legs when you're sitting down.
  • urinary tract infection (UTI) – talk to your pharmacist or doctor if you have symptoms of a UTI. These include needing to pee suddenly or more often, pain when peeing, smelly or cloudy pee, or pain in your lower belly. Drink plenty of water and take paracetamol to ease the pain if you need to. Ask for an urgent doctor's appointment if you also have pain in your sides or lower back, have a very high temperature or feel hot and shivery, have diarrhoea, or are feeling or being sick.

7. Pregnancy and breastfeeding

Olmesartan is not normally recommended in pregnancy or when breastfeeding.

But your doctor may prescribe it if they think the benefits of the medicine outweigh the risks.

If you're trying to get pregnant or already pregnant, talk to your doctor about the benefits and possible harms of taking olmesartan. Other treatments may be safer for you and your baby.

For more information about how olmesartan can affect you and your baby during pregnancy, read this leaflet on the Best Use of Medicines in Pregnancy (BUMPS) website.

Olmesartan and breastfeeding

It's not known whether olmesartan gets into breast milk.

Talk to your doctor, as other medicines may be better when breastfeeding.

Non-urgent advice: Tell your doctor if you're:

  • trying to get pregnant
  • pregnant
  • breastfeeding

8. Cautions with other medicines

There are some medicines that don't mix well with olmesartan.

Before starting olmesartan, tell your doctor if you're taking:

  • other medicines to help lower your blood pressure, especially aliskiren or an ACE inhibitor, such as enalapril, captopril, lisinopril, ramipril
  • anti-inflammatories, such as ibuprofen, naproxen or diclofenac
  • aspirin (if you're taking more than 3g a day)
  • tablets to make you pee more (diuretics)
  • arthritis medicines, such as celecoxib or etoricoxib
  • lithium, a medicine for mental health problems
  • potassium supplements or salt substitutes containing potassium
  • heparin, a medicine for thinning the blood
  • spironolactone, a medicine to treat heart failure
  • colesevelam, a medicine for lowering cholesterol

Mixing olmesartan with herbal remedies or supplements

There's very little information about taking herbal remedies and supplements with olmesartan.

Important: Medicine safety

Tell your doctor or pharmacist if you're taking any other medicines, including herbal medicines, vitamins or supplements.

9. Common questions

How does olmesartan work?

Olmesartan is a type of blood pressure-lowering medicine called an angiotensin receptor blocker.

Like other angiotensin receptor blockers, olmesartan relaxes and widens your blood vessels.

This lowers your blood pressure and makes it easier for your heart to pump blood around your body.

How long does olmesartan take to work?

It usually takes about a week for olmestartan to start reducing high blood pressure.

It may take 2 to 8 weeks to take effect fully.

If you have high blood pressure, you may not have any symptoms. In this case, you may not feel any different when you take olmesartan.

This doesn't mean that it isn't working, and it's important to keep taking your medicine.

How long will I have to take it for?

Usually treatment with olmesartan is long term.

You may even have to take it for the rest of your life.

Is olmesartan safe to take for a long time?

Olmesartan is generally safe to take for a long time. In fact, it works best when you take it for a long time.

Taking olmesartan long term can sometimes cause problems with your kidneys. This means they don't work as well as they should.

Your doctor will check how well your kidneys are working with regular blood tests.

What will happen if I stop taking it?

Talk to your doctor if you want to stop taking olmesartan.

Stopping olmesartan may cause your blood pressure to rise. This may increase your chances of having a heart attack and stroke.

If you're bothered by side effects, your doctor may be able to prescribe a different blood pressure-lowering medicine.

Can I come off olmesartan now my blood pressure is lower?

Even if your blood pressure is successfully lowered by olmesartan, it's best to carry on taking it.

If you stop taking olmesartan, your blood pressure could rise back up again.

If you need blood pressure-lowering medicines, you'll probably need to take 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.

Can I drink alcohol with olmesartan?

Drinking alcohol can increase the blood pressure-lowering effect of olmesartan, which can make you feel dizzy or lightheaded.

During the first few days of taking olmesartan or after a dose increase, it's best not to drink alcohol until you see how the medicine affects you.

If you find olmesartan makes you feel dizzy, it's best to stop drinking alcohol.

Regularly drinking more than the national guidelines can cause or worsen high blood pressure.

Is there any food or drink I need to avoid?

Do not use salt substitutes such as Lo-Salt. This is because they're high in potassium.

When mixed with olmesartan, they may make the level of potassium in your blood too high.

Apart from not drinking too much alcohol, there's nothing else you need to avoid while taking olmesartan.

Eating a healthy, balanced diet can help if you have high blood pressure or heart failure.

Are there similar medicines to olmesartan?

There are several other angiotensin receptor blockers that work in the same way as olmesartan.

They include candesartan, irbesartan, losartan and valsartan.

There are also lots of other types of blood pressure-lowering medicines, such as:

The blood pressure-lowering medicine you're prescribed depends on your age and ethnicity. If you're under 55 you'll usually be offered an ACE inhibitor or an angiotensin receptor blocker. If you're aged 55 or older, or you're any age and of African Caribbean or black African origin, you'll usually be offered a calcium channel blocker.

Many people need to take a combination of different blood pressure-lowering medicines.

But taking angiotensin receptor blockers and ACE inhibitors together isn't usually recommended.

How is it different from other medicines for high blood pressure?

Olmesartan works as well as other angiotensin receptor blockers when it's used to lower blood pressure. Its side effects are also similar.

It also works as well as ramipril and other angiotensin converting enzyme (ACE) inhibitors to lower blood pressure.

Olmesartan can be used by people who have tried taking ramipril or other ACE inhibitors but had to give these up because the medicine gave them a dry, irritating cough.

Can I take olmesartan before surgery?

If you're going to be put to sleep for an operation or dental procedure, tell the doctor or dental surgeon that you're taking olmesartan.

Olmesartan can reduce your blood pressure when it's used with general anaesthetics (that put you to sleep).

Your doctor or dental surgeon will probably advise you to stop taking olmesartan 24 hours before surgery.

Can I take olmesartan for migraines?

There's some evidence that olmesartan might help prevent migraines. But olmesartan is not officially approved for migraines.

Your doctor would probably advise you to try other medicines first.

Can olmesartan protect against Alzheimer's disease?

There have been some studies looking into whether blood pressure medicines could help protect people against Alzheimer's.

But at the moment there's not enough evidence to recommend taking olmesartan or other similar medicines for Alzheimer's.

There are steps you can take that may reduce your risk of Alzheimer's.

If you're worried about getting Alzheimer's disease in the future or have a family history of this condition, speak to your doctor.

Is olmesartan addictive?

No, there's no evidence that olmesartan is addictive.

Will it affect my sex life?

No, there's no evidence that olmesartan will affect your sex life.

Will it affect my fertility?

No, there's no evidence that olmesartan reduces fertility in men or women.

But speak to a pharmacist or your doctor before taking it if you're trying to get pregnant.

Will it affect my contraception?

No, olmesartan won't affect any type of contraception, including emergency contraception.

But some types of hormonal methods of contraception, like the combined pill or contraceptive patch, are not usually recommended for women with high blood pressure.

Talk to your doctor if you're taking combined hormonal contraceptives.

Can I drive or ride a bike?

Olmesartan can make some people feel dizzy, especially when you first start taking it or after taking a bigger dose.

If this happens to you, do not drive a car, ride a bike, or use tools or machinery until you feel better.

Can lifestyle changes help?

You can boost the health of your heart by making some key lifestyle changes.

These will also help if you have high blood pressure or angina:

  • 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.
  • cut down on alcohol – drinking too much alcohol raises blood pressure over time and also makes heart failure worse. Men and women shouldn't drink more than 14 units of alcohol a week. A standard glass of wine (175ml) is 2 units. A pint of lager or beer is usually 2 to 3 units of alcohol.
  • exercise – 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 will help.
  • eat well – aim to eat a diet that includes plenty of fruit and veg, wholegrains, fat-free or low-fat dairy products and lean proteins. It's a good idea to cut down on salt, too. 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.
  • deal with 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, you should have a flu jab every year and a pneumonia vaccination (also called the pneumococcal vaccine) every 5 years. Ask your doctor about these vaccinations. You can have them free on the NHS.

Page last reviewed: 7 January 2019
Next review due: 7 January 2022