Medication · Cardiovascular · full clinical detail
Losartan
An angiotensin receptor blocker (ARB) that relaxes blood vessels to lower blood pressure and protect the kidneys in diabetes, an alternative for people who cough on ACE inhibitors.
Losartan blocks the action of angiotensin II, a hormone that narrows blood vessels and makes the body hold on to salt and water. With the hormone blocked, vessels relax and blood pressure falls, and the heart and kidneys are put under less strain.
NICE: an ARB is offered in place of an ACE inhibitor when the ACE inhibitor is not tolerated (cough), and first-line for adults of Black African or African-Caribbean family origin who need a renin-angiotensin drug
Licensed indications come from the product licence in the named country; guideline-supported and off-label uses are cited to the guideline that supports them. Licensing differs between countries.
How it works
Losartan blocks the action of angiotensin II, a hormone that narrows blood vessels and makes the body hold on to salt and water. With the hormone blocked, vessels relax and blood pressure falls, and the heart and kidneys are put under less strain.
Blocks the AT1 receptor that angiotensin II uses to constrict arteries, release aldosterone from the adrenal glands and thicken heart and vessel walls. With the receptor occupied, arteries relax, pressure falls, and the heart and the kidney's filters are unloaded. Because the converting enzyme is untouched, bradykinin does not build up, so the dry cough of ACE inhibitors is rare.
Mechanism of action
Losartan and its more potent active metabolite (EXP3174) are selective, competitive antagonists at the angiotensin II type 1 (AT1) receptor. Blockade prevents angiotensin II-mediated vasoconstriction, aldosterone secretion, sodium reabsorption, sympathetic activation and the trophic effects on cardiac and vascular tissue. Efferent arteriolar dilatation lowers intraglomerular pressure, which underlies the reduction in proteinuria and slowing of diabetic nephropathy but also the rise in creatinine when renal perfusion depends on angiotensin II (renal artery stenosis, dehydration, NSAIDs). Because ACE is not inhibited, bradykinin is not accumulated and cough and angioedema are much less frequent than with ACE inhibitors. Losartan also has a mild uricosuric effect not shared by other ARBs.
Acute kidney injury when dehydrated, with NSAIDs, or with narrowed renal arteries
High potassium with potassium supplements, spironolactone or kidney disease
Angio-oedema (rare)
Harm to the fetus: stop before or as soon as pregnancy is known
Source: NHS: Losartan. Frequencies follow the source's categories; no percentages are invented.
Serious safety information
Boxed warning (US). US labelling carries a boxed warning on fetal toxicity: drugs that act on the renin-angiotensin system can cause injury and death to the developing fetus, and losartan should be discontinued as soon as pregnancy is detected. US
Special warning. Angioedema (swelling of the face, lips, tongue or throat) is a rare but serious reaction that needs emergency treatment; it is less common than with ACE inhibitors but still possible. UK
Warnings and precautions
Pregnancy. UK information states losartan is not recommended in pregnancy or when trying to conceive, because it can harm the baby, particularly in the second and third trimesters; a different blood-pressure medicine is used. UK
Kidney. Losartan can reduce kidney function and raise potassium, particularly with dehydration, NSAIDs, potassium supplements, potassium-sparing diuretics or narrowed renal arteries; kidney function and potassium are checked before treatment and after dose changes. UK
Precaution. Sick-day guidance: when vomiting, diarrhoea or fever cause dehydration, UK information advises that losartan may need to be paused temporarily to protect the kidneys, restarting once eating and drinking normally. UK
Driving. Dizziness on standing is common at the start; do not drive or use machinery if affected. UK
Contraindications
Factor
Detail
Strength
Country · source
Pregnancy (second and third trimesters)
Contraindicated in the second and third trimesters because of fetal renal failure, oligohydramnios and skull ossification defects; avoid throughout pregnancy.
Aliskiren in people with diabetes or eGFR below 60
Combination with aliskiren is contraindicated in diabetes or with an eGFR below 60 mL/min/1.73 m² because of the risk of hyperkalaemia, hypotension and kidney injury.
"Absolute" and "relative" follow the wording of the cited source; where the source does not classify, the cell is blank.
Interactions
Check interactions
Taking Losartan with other medicines? Add them to the checker to see what the official sources say about each pair: the mechanism, general management and monitoring, never a bare "safe".
Interactions documented in the official sources cited on each card. The list covers the medicines represented on this site and is not exhaustive; how the interaction data is compiled.
Contraindicated or avoidOfficial guidance: avoid the combination
Combining an ACE inhibitor with an angiotensin receptor blocker (dual renin-angiotensin blockade) adds low blood pressure, kidney injury and high potassium without extra benefit.
Why it can occur
pharmacodynamic antagonism · Additive blockade of the same hormone system
What official information says
NICE advises not combining an ACE inhibitor with an ARB to treat hypertension; UK information lists the other class among medicines to tell a doctor about.
What to discuss with a clinician
Official UK guidance: not recommended; a specialist may use the combination in rare circumstances with close monitoring.
Contraindicated or avoidOfficial guidance: avoid the combination
Losartan with any ACE inhibitor (ramipril, lisinopril, enalapril, perindopril) duplicates renin-angiotensin blockade: more hypotension, kidney injury and hyperkalaemia without extra benefit.
Why it can occur
pharmacodynamic antagonism
What official information says
NICE: do not combine an ACE inhibitor with an ARB to treat hypertension.
NSAIDs such as ibuprofen can reduce the blood-pressure-lowering effect of losartan and, particularly with a diuretic or dehydration, cause acute kidney injury and high potassium.
Why it can occur
nephrotoxicity · Loss of the renal prostaglandins that keep the afferent arteriole open when angiotensin II is blocked; the 'triple whammy' with a diuretic
What official information says
UK information advises telling a doctor before taking anti-inflammatory painkillers such as ibuprofen with losartan; the BNF advises monitoring renal function.
What to discuss with a clinician
Official UK guidance: avoid regular NSAID use where possible; if used, kidney function and potassium are checked and the person stays well hydrated.
BNF: Losartan interactions (increased risk of hyperkalaemia; monitor)
Sources
NHS: Losartan(Taking it with other medicines and herbal supplements · Mixing with herbal remedies and supplements)UK BNF: Losartan interactions(Interactions)UK
Review
Facts checked against the cited sources; not yet clinically reviewed · last reviewed 12 September 2026
Losartan + Spironolactone, eplerenone and other potassium-sparing diuretics
ModerateMonitoring or dose adjustment advised
Spironolactone, eplerenone and other potassium-sparing diuretics with losartan increase the risk of hyperkalaemia, particularly with kidney impairment.
Why it can occur
hyperkalaemia risk
What official information says
The BNF advises monitoring serum potassium when these are combined.
What to discuss with a clinician
A common deliberate combination in heart failure under supervision; potassium and kidney function are monitored closely.
Any NSAID (ibuprofen, naproxen, diclofenac, celecoxib, high-dose aspirin) with losartan can reduce its effect and cause acute kidney injury and hyperkalaemia.
Why it can occur
nephrotoxicity
What official information says
UK information advises telling a doctor before taking anti-inflammatory painkillers with losartan; the BNF advises monitoring renal function.
What to discuss with a clinician
Avoid regular use where possible; monitor kidney function and potassium if combined.
Therapeutic duplication. An ARB with another ARB or with an ACE inhibitor duplicates renin-angiotensin blockade; UK guidance advises against combining them for hypertension. UK
Food and drink
With
Effect
Official advice
Potassium-containing salt substitutes (LoSalt and similar)
Losartan reduces aldosterone and so reduces potassium excretion; adding potassium-rich salt substitutes can push potassium to dangerous levels. (hyperkalaemia risk)
UK information advises against using salt substitutes containing potassium without checking with a doctor or pharmacist. UK
Alcohol
Alcohol lowers blood pressure further and increases dizziness and faintness, especially when starting. (Additive hypotension)
UK information states moderate alcohol is usually acceptable once settled on the dose, but it can make side effects worse in the first weeks. UK
Herbal remedies and supplements
With
Effect
Official advice
Potassium supplements
Raised blood potassium (hyperkalaemia), which can cause dangerous heart rhythms
UK information advises not taking potassium supplements or salt substitutes containing potassium with losartan unless a doctor has advised it, with blood tests if they are used together. UK
Monitoring
What
Why
Tests and markers
Source
Kidney function and potassium
Baseline, 1-2 weeks after starting and after each dose increase, then at least yearly; a creatinine rise above 30% or potassium above 6 mmol/L prompts review
Not recommended at any stage; contraindicated in the second and third trimesters. Women planning pregnancy are switched to a safer antihypertensive, and losartan is stopped as soon as pregnancy is confirmed. UK
Breastfeeding
UK information advises against losartan while breastfeeding, particularly for premature or newborn babies, because little is known about the amounts in milk; other medicines with more safety data are preferred. UK
Children
Licensed in the UK for hypertension in children aged 6 years and over at weight-based doses under specialist supervision. UK
Older adults
A lower starting dose (25 mg) is used over 75 years and with intravascular depletion; older adults are more prone to hypotension and to potassium and creatinine changes. UK
Kidney impairment
No dose reduction is needed for mild to moderate impairment, but kidney function and potassium must be monitored more closely; in renal artery stenosis and advanced disease losartan can precipitate acute kidney injury. UK
Liver impairment
A lower dose (25 mg once daily) is used in mild to moderate hepatic impairment; avoid in severe impairment. UK
Losartan is contraindicated with aliskiren in diabetes, and dual blockade with an ACE inhibitor is not recommended; monitoring of potassium and creatinine is intensified in people with diabetes.
Chronic kidney disease: losartan is used to protect the kidney, but creatinine and potassium must be monitored and the drug reviewed if creatinine rises by more than 30% or potassium exceeds 6 mmol/L.
Bilateral renal artery stenosis (or stenosis in a single functioning kidney): losartan can cause acute kidney failure because filtration depends on angiotensin II in these kidneys.
Heart failure: started at a low dose under specialist supervision because of hypotension and kidney effects; used when ACE inhibitors are not tolerated.
Educational summary of drug–condition cautions in the cited sources; not a personal screening.
Effects on tests and results
Creatinine: A small rise in serum creatinine and fall in eGFR is expected when losartan is started; a rise of more than about 30% prompts investigation. UK
Potassium: Serum potassium rises because aldosterone release is reduced; hyperkalaemia is more likely with kidney disease, potassium supplements, spironolactone or NSAIDs. UK
Losartan modestly lowers serum urate (a uricosuric effect not shared by other ARBs). UK
Urine protein: Urine albumin excretion falls in diabetic kidney disease; this is the intended effect and is followed with the albumin-to-creatinine ratio. UK
Pharmacokinetics
Absorption
Well absorbed; oral bioavailability about 33% because of first-pass metabolism; food slows but does not reduce absorption
Peak
Losartan 1 hour, active metabolite 3-4 hours
Half-life
Losartan about 2 hours; the active carboxylic-acid metabolite 6-9 hours, which allows once-daily dosing
Metabolism
Liver, mainly CYP2C9 (and CYP3A4) to the active metabolite EXP3174
Elimination
About 35% in urine and 60% in faeces, as metabolites; not removed by haemodialysis
Dosing is intentionally not described: doses depend on the indication, the country's licence, kidney and liver function, age, weight and other medicines, and are set by a prescriber.
Medicines that share the class of Losartan. They are separate medicines with their own licences, doses and interactions, not alternative names for Losartan.
Medicines often discussed alongside Losartan: used together, compared with it, or acting on the same problem by a different route.
Educational content. Anatomy Nexus provides medical education and does not replace professional medical advice, diagnosis, treatment, prescribing or pharmacist review. Doses, choices and monitoring are decided by a prescriber for an individual; never start, stop or change a medicine on the basis of this page.
