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 of olmesartan happen in more than 1 in 100 people.
There are things you can do to help cope with them:
Feeling dizzy or tired
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, ride a bike or use tools or machines if you feel dizzy.
Headaches, flu-like symptoms, runny or stuffy nose, cough or bronchitis
Rest and drink plenty of fluids. Do not drink too much alcohol if you get headaches. 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.
Pain in your back, bones or joints
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) or indigestion
Try taking your tablets with or after a meal or snack. Take small, frequent sips of water or squash to prevent dehydration. 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.
Stomach ache
Try to rest and relax. It can help to eat and drink slowly and have smaller and more frequent meals.
Putting a heat pad or covered hot water bottle on your stomach may also help. If you are in a lot of pain, speak to your pharmacist or doctor.
Diarrhoea
Drink plenty of water or squash to prevent dehydration. Signs of dehydration include 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. Speak to a pharmacist before taking any medicine to treat diarrhoea.
If you take the combined pill or progestogen-only pill and you have severe diarrhoea for more than 24 hours, your contraception may not protect you from pregnancy. Check the pill packet for advice.
Swollen feet, ankles, legs or hands (oedema)
Raise your legs when you're sitting down.
Urinary tract infection (UTI)
Contact your doctor if you have symptoms of a UTI as you may need treatment. Symptoms 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.
Talk to your doctor or pharmacist if the advice on how to cope does not help and these side effects bother you or do not go away.
Serious side effects
Some people have serious side effects after taking olmesartan.
Call a doctor or call 111 straight away if you have:
- blood in your pee
- severe diarrhoea that does not go away and causes noticeable weight loss
- a rash or tiny reddish-purple spots under the skin (this may be less obvious on black or brown skin), cuts that will not 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
Immediate action required: Call 999 now if:
- you get chest pain that does not stop after a few minutes – chest pain is a possible sign of a heart attack and needs to be checked as soon as possible
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to olmesartan.
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Long-term side effects
Taking olmesartan for a long time can sometimes 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 olmesartan. For a full list, see the leaflet inside your medicines packet.
Reporting side effects
You can report any suspected side effect using the Yellow Card safety scheme.
Visit the Yellow Card website for more information about reporting side effects.