Pharmacology · Angiotensin II receptor blockers (ARBs)
Losartan !
A blood pressure medicine that blocks the receptor for angiotensin II. It protects the kidneys in diabetes and rarely causes cough.
Updated 2026-11-01
The figure shows olmesartan, another ARB of the same class, in the same binding pocket of the human AT1 receptor; no structure with losartan bound is available.
Mechanism of action
Losartan and its more potent active metabolite block the AT1 receptor, so angiotensin II cannot constrict arterioles, release aldosterone or drive cardiac and vascular remodelling. The block works whatever the source of angiotensin II. ACE keeps working, so bradykinin is not raised and cough is rare.
- Losartan and its metabolite occupy the AT1 receptor
- Angiotensin II can no longer activate it
- Arterioles dilate and aldosterone falls
- Blood pressure and strain on heart and kidney fall
Pharmacokinetics
- Absorption
- Absorbed by mouth, with marked first-pass metabolism
- Metabolism
- In the liver (CYP2C9 and CYP3A4) to an active carboxylic acid metabolite that does much of the work
- Elimination
- Through bile and urine
- Half-life
- About 2 hours for losartan and about 6 to 9 hours for its active metabolite
Indications
- High blood pressure, including with left ventricular hypertrophy Arterial hypertension →
- Heart failure, mainly when an ACE inhibitor is not tolerated Heart failure →
- Kidney disease in type 2 diabetes with hypertension Chronic kidney disease →
Adverse effects
Common
- Dizziness, especially on standing
- Hyperkalaemia
- Rise in creatinine
- Muscle cramps or back pain
Contraindications
- Pregnancy
- Use with aliskiren in people with diabetes
Key interactions
- Potassium-sparing diuretics or potassium supplements
- Higher risk of hyperkalaemia
- NSAIDs
- Weaker blood pressure effect and higher risk of kidney injury
- ACE inhibitors
- Dual blockade: more hyperkalaemia, hypotension and kidney injury
- Lithium
- Higher lithium levels
What is monitored
- Blood pressure
- Potassium
- Creatinine and kidney function
Test yourself
Think of the answer, then tap the question to see it.
How does losartan differ from enalapril in mechanism?
Losartan blocks the AT1 receptor; enalapril blocks ACE, the enzyme that makes angiotensin II. Losartan leaves ACE working, so bradykinin does not accumulate.
Which combination with losartan is contraindicated in people with diabetes?
Losartan with aliskiren, a direct renin inhibitor: blocking the same system twice raises the risk of hypotension, hyperkalaemia and kidney injury.
Why does losartan's effect last longer than its own half-life suggests?
The liver converts it into an active metabolite that is more potent and has a longer half-life.
Related drugs
Related conditions
← Back to the class: Angiotensin II receptor blockers (ARBs)
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Losartan: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2018); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025); DailyMed - LOSARTAN POTASSIUM TABLETS, 25 MG- losartan potassium tablet (DailyMed (U.S. National Library of Medicine), 2026).
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Representative model, for educational purposes only.