ARBs
Olmesartan
An ARB that relaxes blood vessels to lower blood pressure; often used when an ACE inhibitor causes a cough.
What is Olmesartan?
Olmesartan is an angiotensin-receptor blocker (ARB) used to treat high blood pressure. It relaxes blood vessels by blocking the action of a hormone that narrows them, which lowers blood pressure. It is often chosen as an alternative when an ACE inhibitor has caused a troublesome dry cough, and kidney function and potassium are checked with blood tests.
Education and reference only. This is a plain-language guide to Olmesartan — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Olmesartan is an angiotensin-receptor blocker (ARB) used in the UK to treat high blood pressure. It works on the same hormone system as ACE inhibitors but blocks the hormone at its receptor instead, which means it relaxes blood vessels without usually causing the dry cough that ACE inhibitors can. It is taken regularly as a long-term medicine, with blood tests to check the kidneys and potassium, and the benefit is in lower cardiovascular risk over time.
How it works
Olmesartan blocks the receptors that angiotensin II acts on. Angiotensin II is a hormone that narrows blood vessels and makes the body hold on to salt and water. By blocking its receptors, olmesartan allows blood vessels to relax and widen, so blood pressure falls. Because it does not raise the natural substances that cause the ACE-inhibitor cough, a dry cough is much less likely with this medicine.
Company & origin
Originated / developed by: Developed by Sankyo (now Daiichi Sankyo)..
Olmesartan is an angiotensin-receptor blocker (ARB) introduced in the early 2000s and marketed in the UK as Olmetec for high blood pressure.
What it treats
Conditions Olmesartan is used for
Practical use
How to take Olmesartan
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it regularly as prescribed, at about the same time each day.
- Tell your prescriber if you develop severe, ongoing diarrhoea or unexplained weight loss.
- Avoid salt substitutes that are high in potassium unless advised, as they can raise potassium.
- Stand up slowly when you first start, as it can cause dizziness.
- If you miss a dose, take it as soon as you remember unless it is nearly time for the next one — do not double up.
- Do not stop it on your own without advice, as your blood pressure may rise again.
Weighing it up
Advantages & disadvantages of Olmesartan
Advantages
- It rarely causes the dry cough seen with ACE inhibitors, so it suits people who could not tolerate one.
- It is effective at lowering blood pressure and helps protect the kidneys in some people.
- It is usually taken once a day, which is convenient.
Disadvantages
- It must not be used in pregnancy and is stopped if pregnancy is planned.
- It needs blood tests to monitor the kidneys and potassium.
- Very rarely it can cause severe ongoing diarrhoea with weight loss (sprue-like enteropathy).
- Like other blood-pressure medicines it can cause dizziness, especially when starting.
Practical use
Good to know
Olmesartan is taken regularly to keep blood pressure controlled. It is often used when an ACE inhibitor has caused a cough, as it is much less likely to do so. Blood tests check your kidneys and potassium. It must not be used in pregnancy. Very rarely it can cause severe, ongoing diarrhoea with weight loss (a sprue-like enteropathy); if this happens, tell your doctor, as it usually settles when the medicine is stopped. Avoid potassium-containing salt substitutes unless advised.
Who should not take it / use with caution
- Women who are pregnant, planning pregnancy or breastfeeding.
- People with severe kidney problems or certain narrowings of the kidney arteries, used with caution and monitoring.
- It is generally not combined with an ACE inhibitor, as together they raise the risk of kidney problems and high potassium.
Monitoring
- Blood tests for kidney function and potassium when starting, after changes and periodically.
- Regular blood-pressure checks.
- Reviewing any severe or ongoing diarrhoea, which is a rare but recognised effect.
Side effects
- Dizziness, especially when starting or standing up.
- Headache or tiredness.
- A rise in blood potassium in some people.
- Very rarely, severe ongoing diarrhoea with weight loss (sprue-like enteropathy).
Key interactions
- Anti-inflammatory painkillers (NSAIDs such as ibuprofen), which can reduce its effect and affect the kidneys.
- Potassium supplements, potassium-containing salt substitutes and certain water tablets, which can raise potassium.
- Other blood-pressure-lowering medicines and lithium, which need extra care.
Available as: Tablets.
Answers
Olmesartan: frequently asked questions
How is olmesartan different from an ACE inhibitor?
Olmesartan is an ARB. It works on the same hormone system as ACE inhibitors but is much less likely to cause a dry cough, which is why it is often used as an alternative when an ACE inhibitor has caused a cough.
Can I take olmesartan in pregnancy?
No — ARBs such as olmesartan should not be used in pregnancy. If you are pregnant or planning a pregnancy, tell your prescriber so it can be changed to a safer option.
I have ongoing diarrhoea on olmesartan — should I worry?
Tell your doctor. Very rarely olmesartan can cause severe, persistent diarrhoea with weight loss (a sprue-like enteropathy). It usually settles once the medicine is stopped, but it needs checking.
Why do I need blood tests on olmesartan?
Blood tests check your kidney function and potassium level. They are usually done when you start, after any change and from time to time afterwards.
Should I avoid certain salts on olmesartan?
Yes — avoid salt substitutes that are high in potassium unless your prescriber says otherwise, as olmesartan can raise potassium and these add to that effect.
The wider class
About ARBs
Olmesartan belongs to the arbs class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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