Quick facts
| Generic name | losartan potassium |
|---|---|
| Brand names | Cozaar |
| Drug class | Angiotensin II receptor blocker (ARB) |
| Generally used for | Lowers blood pressure, reduces stroke risk in people with high blood pressure and thickened heart muscle, and protects the kidneys in type 2 diabetes. |
Health Captain explains what a medicine is generally used for, how its class works, and what to discuss with your care team. We never publish dosing, and this page cannot account for your medical history, kidney or liver function, pregnancy, or the other medicines you take. This is education, not prescribing advice — follow the instructions on your label and ask your prescriber or pharmacist.
What is Losartan?
Losartan is an angiotensin II receptor blocker. Instead of stopping the body from making angiotensin II, it blocks the receptor that hormone acts on, so blood vessels stay relaxed and less salt and water are retained. It is often chosen when an ACE inhibitor causes a cough, because it does not raise bradykinin in the same way.
Key takeaways
- ARBs and ACE inhibitors act on the same hormone system at different points and lower blood pressure to a similar degree.
- Losartan rarely causes the ACE inhibitor cough, which is the usual reason people are switched to it.
- Like ACE inhibitors, it raises potassium and carries an FDA boxed warning about fetal toxicity.
- It is not combined with an ACE inhibitor — dual blockade adds harm without adding benefit for most people.
- This page is general education, not prescribing advice — whether this medicine is right for you, and how it is dosed, is individualized and decided by you and your prescriber.
How it generally works
Angiotensin II is the hormone that narrows arteries and tells the body to hold sodium and water. ACE inhibitors stop it being made; losartan takes the other approach and blocks the receptor it binds to. The end result on blood pressure is similar, but the route is different, and that difference explains most of the practical distinctions between the two classes.
Because losartan does not interfere with the enzyme that breaks down bradykinin, it very rarely causes the dry cough associated with ACE inhibitors, and angioedema is less common — though not impossible. Blocking the same hormone system also lowers pressure inside the kidney’s filtering units, which is the basis for its use in protecting kidneys in type 2 diabetes with protein in the urine.
Common side effects
Most people tolerate Losartan well, and many effects settle as the body adjusts. Tell your prescriber or pharmacist about anything that persists or bothers you.
- Dizziness or lightheadedness, particularly early on
- Fatigue
- A rise in blood potassium on lab work
- Headache
- Nasal congestion or upper respiratory symptoms
- Muscle cramps or back pain
Serious side effects
These are uncommon, but they are the ones to act on rather than wait out. Contact a clinician promptly if you notice any of them. If you believe you are experiencing a medical emergency, call emergency services immediately (911 in the United States).
- Swelling of the lips, tongue, face, or throat — angioedema is uncommon with ARBs but has been reported and is an emergency
- Marked reduction in urine output, swelling, or a sharp rise in creatinine — acute kidney injury, particularly with dehydration or narrowed kidney arteries
- Muscle weakness or an irregular heartbeat — may reflect high potassium
- Fainting — excessive blood pressure lowering, especially with volume depletion
Important warnings
FDA boxed warning
A boxed warning is the strongest warning the US Food and Drug Administration applies to a medicine. It does not mean nobody should take it — it means the risk below is serious enough that it must be weighed deliberately with your prescriber.
- Fetal toxicity — ARBs carry an FDA boxed warning. Drugs acting on the renin-angiotensin system can injure or kill a developing fetus and are stopped as soon as pregnancy is detected.
Other warnings and precautions
- Hyperkalemia — losartan is a potassium salt and blocks aldosterone signaling, so potassium can rise, especially with kidney disease, diabetes, potassium supplements, or salt substitutes.
- Kidney function — worsening kidney function can occur, particularly with volume depletion, heart failure, or bilateral renal artery narrowing.
- Symptomatic hypotension — most likely in people who are dehydrated or on high-dose diuretics.
- Avoid dual blockade — do not combine with an ACE inhibitor, and avoid combining with aliskiren in diabetes or reduced kidney function.
Drug interactions
Interactions are one of the most common avoidable medication problems. Keep one list of everything you take — including supplements and over-the-counter products — with the Medication List Builder, and read our guide to drug interactions.
- Potassium supplements, potassium-containing salt substitutes, and potassium-sparing diuretics — additive rise in potassium.
- NSAIDs — reduce the blood pressure effect and, especially alongside a diuretic, increase acute kidney injury risk.
- Lithium — ARBs can raise lithium levels toward toxicity.
- ACE inhibitors and aliskiren — dual blockade of the same system is generally avoided.
- Rifampin — can reduce losartan’s active metabolite and blunt its effect.
- Other antihypertensives and diuretics — additive blood pressure lowering, often intended.
Monitoring
What a care team typically keeps an eye on while someone is taking Losartan. The exact schedule is individual.
- Blood pressure, including home readings
- Serum potassium and creatinine after starting or changing, then periodically
- Urine albumin in people with diabetes or chronic kidney disease
Storage
- Store tablets at room temperature in the original container, away from moisture.
- Do not use tablets past the printed expiry date.
- Keep out of reach of children.
Questions for your doctor or pharmacist
Pharmacists are the most under-used resource in medicine, and the conversation is usually free. Build an agenda with Appointment Prep.
- Can we go through my full medication list together — prescriptions, over-the-counter products, vitamins, herbal products, and supplements — to check for interactions, duplicates, and anything I no longer need?
- Am I on this for blood pressure alone, or also to protect my kidneys or reduce stroke risk?
- When should potassium and kidney function be rechecked?
- Should I avoid potassium-containing salt substitutes?
- Could I become pregnant, and what would we switch to if so?
- What home blood pressure readings would mean this needs adjusting?
Frequently asked questions
Is an ARB better than an ACE inhibitor?
For blood pressure and most cardiovascular outcomes they perform similarly. ARBs cause far less cough and somewhat less angioedema; ACE inhibitors have a longer outcome-trial record in some settings and are often cheaper. The choice usually comes down to tolerance, other conditions, and cost, and is made with your prescriber rather than by class alone.
Can I take losartan if I had angioedema on lisinopril?
Sometimes, but cautiously and only under a prescriber’s direction. Angioedema with ARBs is rarer, but a small share of people who reacted to an ACE inhibitor also react to an ARB. This is a decision that requires reviewing exactly what happened, how severe it was, and what alternatives exist.
Why does losartan raise potassium?
Angiotensin II normally stimulates aldosterone, the hormone that makes the kidney excrete potassium. Blocking the angiotensin receptor lowers aldosterone, so less potassium leaves in urine. In most people the rise is small. It matters more with reduced kidney function, diabetes, potassium supplements, salt substitutes, or potassium-sparing diuretics — which is why blood tests are scheduled.
Sources
- MedlinePlus — Drugs, Herbs and Supplements — Plain-language drug information from the US National Library of Medicine; search for losartan.
- DailyMed — losartan labeling — The current FDA-approved prescribing information submitted by manufacturers.
- American Heart Association — High Blood Pressure — Patient information on blood pressure treatment and monitoring.
- NHLBI — High Blood Pressure — US National Institutes of Health patient information.
- FDA — Drug Safety and Availability — Safety communications, label changes, recalls, and shortage notices.
Health Captain links to primary public-health and clinical sources so you can read the original material yourself. See our sources policy.