Losartan lowers blood pressure by blocking the hormone that narrows blood vessels. It is also used to protect the kidneys in diabetes, to treat heart failure, and to reduce stroke risk. It is taken once daily, long term, and it does not cause the dry cough that ACE inhibitors do.
What is Losartan?
The South African Medicine Price Registry lists losartan under many names, all Schedule 3:
| Brands | Strengths |
|---|---|
| Austell Losartan, Losartan Biotech, Annin, Zartan, Normoten, Zaario | 50 mg, 100 mg |
| Losartan Comp / Co versions | Losartan with hydrochlorothiazide 12.5 mg or 25 mg |
Being given a different brand is ordinary generic substitution.
Losartan is an angiotensin II receptor blocker (ARB). The body has a hormone system — the renin-angiotensin system — that raises blood pressure when it detects a fall. Its final messenger, angiotensin II, narrows blood vessels and prompts salt and water retention.
ACE inhibitors such as enalapril stop angiotensin II being made. ARBs such as losartan block its receptor instead, so it is produced but cannot act.
That difference explains the main practical distinction between them. ACE inhibitors also block the breakdown of bradykinin, which accumulates in the airways and causes a persistent dry cough in a meaningful proportion of people — often months after starting, and frequently not connected to the medicine. ARBs do not cause that cough, which is why people who cough on an ACE inhibitor are usually switched to one.
The “Comp” or “Co” versions add hydrochlorothiazide, a diuretic. Combining a blood pressure medicine with a low-dose diuretic controls blood pressure better than pushing either to its maximum — being moved to a combination tablet is usually good prescribing rather than a sign of deterioration.
What is Losartan commonly used for?
- High blood pressure (hypertension) — the main use, alone or combined.
- Protecting the kidneys in type 2 diabetes, where losartan specifically has evidence for slowing progression of diabetic kidney disease. This is an important use and is often the reason it is chosen over other classes.
- Chronic kidney disease with protein in the urine, reducing protein leakage and slowing decline.
- Heart failure, particularly where an ACE inhibitor is not tolerated.
- Reducing stroke risk in people with high blood pressure and left ventricular hypertrophy — thickening of the heart muscle.
- After a heart attack, in some prescribing.
- Lowering uric acid, a minor additional effect that can be useful in people with gout.
Two points about what treating blood pressure means:
It is preventive, not symptomatic. High blood pressure causes no symptoms until it causes a stroke, heart attack or kidney failure. Nobody feels better on treatment — which is exactly why so many people stop, and why that decision is so costly.
It is usually lifelong. Blood pressure rises again within weeks of stopping. A normal reading on treatment means the medicine is working, not that it is no longer needed.
Lifestyle still matters alongside: reducing salt, losing excess weight, regular activity, moderating alcohol and stopping smoking all lower blood pressure genuinely.
How Losartan fits into this medicine category
| Group | Examples | How it works |
|---|---|---|
| ARBs | Losartan, telmisartan, valsartan | Block angiotensin II at its receptor; no cough |
| ACE inhibitors | Enalapril, perindopril | Block angiotensin II production; can cause dry cough |
| Calcium channel blockers | Amlodipine (Ciplavasc) | Relax arteries |
| Thiazide diuretics | Hydrochlorothiazide (Ridaq), indapamide | Remove salt and water |
| Beta blockers | Carvedilol, bisoprolol | Slow the heart |
| Mineralocorticoid blockers | Spironolactone | Resistant hypertension, heart failure |
ACE inhibitors and ARBs should not be combined — the risks compound without added benefit. See the heart and blood pressure medicines hub.
What to check before using Losartan
Losartan must not be taken in pregnancy. ARBs cause serious harm to a developing baby, particularly in the second and third trimesters — kidney failure, skull defects and death. If you are pregnant or planning pregnancy, tell your doctor so it can be changed before conception, not after. Anyone of childbearing age should know this at the outset.
Tell your doctor or pharmacist if you:
- Have kidney disease or renal artery stenosis — narrowing of the arteries to the kidneys, where ARBs can cause a sharp fall in kidney function.
- Have high potassium, or take potassium supplements or salt substitutes, which are usually potassium chloride. ARBs raise potassium, and this is a genuinely under-appreciated combination.
- Take potassium-sparing diuretics — spironolactone, amiloride, eplerenone.
- Take lithium, whose levels rise substantially with ARBs.
- Take anti-inflammatories regularly. NSAIDs reduce the blood pressure effect and, combined with an ARB and a diuretic, can damage the kidneys — a combination sometimes called the “triple whammy”.
- Have liver disease, heart failure, or aortic or mitral valve narrowing.
- Are dehydrated, or have been vomiting or had diarrhoea — blood pressure can drop sharply.
- Are breastfeeding.
Practical points:
- Take it once daily at the same time, with or without food.
- Keep your blood tests. Kidney function and potassium are checked before starting and periodically after — this is routine, not a sign of a problem.
- Get up slowly at first, particularly after the first dose or a dose increase.
- Suspend it temporarily during a vomiting or diarrhoea illness if your doctor has advised sick-day rules, and contact them — dehydration plus an ARB is hard on the kidneys.
- Do not stop because your reading is normal.
Possible cautions and when to ask a pharmacist or doctor
Losartan is generally well tolerated. Common effects are dizziness, particularly at first, tiredness, headache and occasionally a raised potassium level.
Get emergency help for:
- Swelling of the face, lips, tongue or throat, or difficulty breathing or swallowing — angioedema. It is much less common with ARBs than ACE inhibitors but can occur, and it can obstruct the airway.
- Fainting, or severe dizziness.
- Chest pain or severe breathlessness.
- Muscle weakness, palpitations or an irregular heartbeat — possible high potassium, which can cause dangerous heart rhythms.
Contact your doctor if:
- Blood pressure readings stay high, or fluctuate widely.
- You develop marked dizziness on standing.
- You have a vomiting or diarrhoea illness and cannot drink normally.
- You notice reduced urine output or swollen ankles.
- Another prescriber starts you on a new medicine, particularly an anti-inflammatory or a potassium-containing product.
- You are pregnant, or planning to be — this needs changing.
- You are running low on tablets. Do not let them run out.
Related medicine guides
Frequently asked questions
What is losartan 50 mg used for? Lowering high blood pressure, protecting the kidneys in type 2 diabetes, treating heart failure and reducing stroke risk. 50 mg is the usual starting strength.
What is losartan used for in the body? It blocks angiotensin II, a hormone that narrows blood vessels and causes salt and water retention. Blocking it relaxes the vessels and lowers pressure.
How is it different from an ACE inhibitor? Both act on the same hormone system, but ARBs block the receptor rather than the enzyme — so they do not cause the persistent dry cough ACE inhibitors are known for.
Can I take it in pregnancy? No. ARBs cause serious harm to a developing baby. Tell your doctor before conceiving so it can be changed.
Can I stop when my blood pressure is normal? No. A normal reading means the medicine is working. Blood pressure rises again within weeks of stopping.
Can I use a salt substitute? Ask first. Most are potassium chloride, and losartan already raises potassium.
Can I take ibuprofen with it? Not regularly without advice. Anti-inflammatories reduce its effect and, with a diuretic, can affect the kidneys.
Why do I need blood tests? To check kidney function and potassium, both of which losartan affects.