An angiotensin-receptor blocker (ARB)
Losartan
An angiotensin-receptor blocker (ARB) for high blood pressure and heart failure, often used when an ACE inhibitor causes a cough.
What is Losartan?
Losartan is an angiotensin-receptor blocker (ARB) that relaxes blood vessels to lower blood pressure. It is used for high blood pressure and heart failure and to help protect the kidneys, and is often chosen for people who cannot tolerate the cough caused by ACE inhibitors.
Education and reference only. This is a plain-language guide to Losartan — 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
Losartan is a widely used angiotensin-receptor blocker (ARB). It lowers blood pressure, is used in heart failure with a reduced pumping function, and helps protect the kidneys — for example in people with diabetes or chronic kidney disease who have protein in the urine. ARBs work on the same hormone system as ACE inhibitors but rarely cause the dry cough, so losartan is a common choice when an ACE inhibitor is not tolerated. It is a long-term, once-daily tablet.
How it works
Losartan blocks the receptor that angiotensin II acts on, rather than blocking the enzyme that makes it. Angiotensin II is a hormone that tightens blood vessels and makes the body hold on to salt and water; by stopping it from reaching its receptor, losartan lets blood vessels relax and reduces fluid load, so blood pressure falls and the heart has less to work against. Because it acts one step further along than an ACE inhibitor, it does not build up the airway chemicals that cause the ACE-inhibitor cough.
Company & origin
Originated / developed by: Merck & Co. (discovered at DuPont).
Losartan was discovered by scientists at DuPont (later DuPont Merck) and was the first non-peptide angiotensin II receptor blocker (ARB). It was approved by the FDA in 1995 and marketed by Merck & Co. as Cozaar.
What it treats
Conditions Losartan is used for
Practical use
How to take Losartan
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Usually taken once a day at about the same time.
- Swallow the tablet with water, with or without food.
- If you miss a dose, take it when you remember unless it is nearly time for the next one, then skip it.
- Avoid NSAID painkillers and potassium-based salt substitutes unless your doctor advises.
- Do not stop without advice, particularly if taken for heart failure or kidney protection.
Weighing it up
Advantages & disadvantages of Losartan
Advantages
- Effective blood-pressure lowering without the cough seen with ACE inhibitors.
- Once-daily dosing.
- Useful for kidney protection in diabetes.
- Cheap, well-established generic.
Disadvantages
- Can raise potassium and affect kidney function, so needs blood-test monitoring.
- May cause dizziness, especially when starting.
- Must be avoided in pregnancy.
- Does not relieve symptoms you can feel — the benefit is long-term protection.
Practical use
Good to know
It is taken once a day at a consistent time, often started low and built up, with a blood-pressure and blood-test check after starting and after increases. Its big practical advantage over ACE inhibitors is that it rarely causes a dry cough, which is why people are often switched to it. Like ACE inhibitors, it raises blood potassium in some people and is avoided in pregnancy. Anti-inflammatory painkillers (NSAIDs), especially with a water tablet, can stress the kidneys.
Who should not take it / use with caution
- People who are pregnant or planning pregnancy — ARBs are avoided in pregnancy and switched beforehand.
- Used with caution in significant kidney artery narrowing, low blood pressure, or a high blood potassium level.
- It is not normally combined with an ACE inhibitor, as together they raise the risk of kidney problems and high potassium.
Monitoring
- Blood pressure
- Kidney function and blood potassium before and after starting/increasing
- Tolerability
Side effects
- Dizziness or light-headedness, especially on standing or when starting.
- A rise in blood potassium or a change in kidney function (watched with blood tests).
- Generally well tolerated; unlike ACE inhibitors it rarely causes a dry cough, and angioedema is very rare.
Key interactions
- NSAID painkillers (e.g. ibuprofen) can reduce its effect and stress the kidneys, especially alongside a diuretic.
- Potassium supplements, potassium-based salt substitutes and certain diuretics can push potassium too high.
- Care with other blood-pressure-lowering medicines, with ACE inhibitors, and with lithium.
Available as: Tablets (several strengths).
Answers
Losartan: frequently asked questions
What is the difference between losartan and an ACE inhibitor like ramipril or lisinopril?
Both work on the same hormone system and lower blood pressure to a similar degree. ACE inhibitors (ramipril, lisinopril) can cause a dry, tickly cough; losartan and other ARBs act one step further along and rarely cause cough, so they are the usual switch when an ACE inhibitor is not tolerated. ACE inhibitors are often tried first, with an ARB as the alternative.
Why was I switched from an ACE inhibitor to losartan?
The most common reason is a persistent dry cough from the ACE inhibitor. Losartan controls blood pressure in much the same way but rarely causes that cough, so it is a well-matched alternative.
Should I take losartan in the morning or at night?
It can be taken once a day at a consistent time that suits you. If you feel dizzy when starting, your prescriber may suggest taking the first dose at bedtime. Follow their advice.
Can I take ibuprofen with losartan?
Occasional use may be fine, but regular anti-inflammatory painkillers (NSAIDs) can reduce losartan's effect and, especially alongside a water tablet, can harm the kidneys. Check with your pharmacist and prefer paracetamol where suitable.
What is the difference between losartan and Cozaar?
They are the same medicine — losartan is the generic (active-ingredient) name and Cozaar is a brand name. Generic losartan contains the identical active ingredient.
The wider class
About ARBs (angiotensin-receptor blockers)
Losartan belongs to the arbs (angiotensin-receptor blockers) 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: Losartan potassium.
- electronic Medicines Compendium (SmPC): Losartan (Cozaar).
- NICE CKS: Losartan.
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