Losartan (Cozaar): How It Works, Uses, Dosage, Side Effects and Complete 2026 Guide
Losartan, sold under the brand name Cozaar and widely available as an inexpensive generic, is one of the most commonly prescribed blood pressure medicines in the United States. It belongs to a class called angiotensin II receptor blockers (ARBs). Doctors often choose it for people who develop the dry cough that can come with ACE inhibitors such as lisinopril, because ARBs protect the heart and kidneys in a similar way without causing that cough.
Despite its popularity, many people take losartan without knowing a few key points: it carries a boxed warning for pregnancy, it can raise potassium, common pain relievers can weaken it and strain the kidneys, and it has a specific role in protecting the kidneys of people with type 2 diabetes. This guide explains how losartan works, what it is approved for, how it is dosed, what to expect, and when to contact a clinician.
If you have just been switched from an ACE inhibitor, read our companion guide: [Lisinopril (ACE Inhibitor): Uses, Dosage and Complete 2026 Guide]
How Losartan Works
Blood pressure is partly controlled by a hormone system called the renin-angiotensin-aldosterone system. One of its main messengers, angiotensin II, tightens blood vessels, signals the body to hold on to salt and water, and over time strains the heart and kidneys.
Losartan blocks angiotensin II from attaching to its AT1 receptor. With the receptor blocked:
Blood vessels relax and widen, so blood pressure falls.
The body holds less salt and water.
The harmful long-term effects of angiotensin II on the heart and kidneys are reduced.
How this differs from an ACE inhibitor: ACE inhibitors stop angiotensin II from being made, and in doing so they also allow a substance called bradykinin to build up, which causes the dry cough and, rarely, swelling of the face and throat. Losartan blocks the receptor instead and does not raise bradykinin in the same way, so cough is not a typical side effect. Angioedema is still possible with ARBs, but it is less common.
Losartan also has a mild uric-acid-lowering effect, which can be a small advantage in people who also have gout.
What Losartan Is Approved For
According to the current US prescribing information (last reviewed on Drugs.com in January 2026), losartan is approved for three uses:
Use | What it means | Notes |
Hypertension (high blood pressure) | Lowers blood pressure to reduce the risk of strokes, heart attacks and kidney problems | Can be used alone or with other blood pressure medicines |
Hypertension with left ventricular hypertrophy (LVH) | Reduces the risk of stroke in people with high blood pressure and a thickened left heart chamber | The label notes this stroke benefit may not apply to Black patients |
Nephropathy in type 2 diabetes | Slows kidney damage in people with type 2 diabetes, a history of high blood pressure, raised creatinine and significant protein in the urine (urine albumin-to-creatinine ratio of 300 mg/g or more) | Protects the kidneys beyond lowering blood pressure |
The label also notes that some blood pressure medicines have smaller effects when used alone in Black patients, which is one reason doctors often combine losartan with another medicine such as a diuretic or amlodipine in this group.
Doctors also use losartan off label in some people with heart failure who cannot take an ACE inhibitor, and in chronic kidney disease with protein in the urine.
Dosage and How to Take It
Situation | Usual dosing (from the prescribing information) |
Hypertension, adults | Starting dose 50 mg once daily; may be increased to 100 mg once daily |
If blood pressure is still not controlled | The doctor may add hydrochlorothiazide 12.5 mg, and/or raise losartan to 100 mg and then increase hydrochlorothiazide to 25 mg |
Hypertension with LVH | Starting dose 50 mg once daily, with hydrochlorothiazide added or the dose increased as needed |
Diabetic nephropathy | Starting dose 50 mg once daily; increased to 100 mg once daily based on blood pressure response |
Mild to moderate liver impairment | Recommended starting dose 25 mg once daily |
Possible low fluid or salt levels (for example, on high-dose diuretics) | The doctor may start at a lower dose; the label advises correcting fluid or salt depletion first |
Practical points:
Losartan is taken by mouth once daily, with or without food. Take it at about the same time each day.
It starts to work within hours, but the full blood pressure effect usually takes several weeks. Doctors often review the dose after about 3 to 6 weeks.
The prescribing information reports no withdrawal symptoms on stopping, but blood pressure will rise again. Do not stop on your own.
If you miss a dose, take it when you remember unless it is nearly time for the next dose. Do not double up.
Side Effects
Common side effects (usually mild and often improve with time):
Dizziness or lightheadedness, especially when standing up
Tiredness
Stuffy or runny nose
Diarrhea or stomach upset
Back or leg pain
Less common but important:
Low blood pressure, with fainting. This is more likely if you are dehydrated, taking a diuretic, or have a heavy fluid loss from vomiting or diarrhea.
High potassium (hyperkalemia). Studies found this more often in people taking losartan for diabetic nephropathy than for high blood pressure alone.
Worsening kidney function, especially in people with narrowed kidney arteries, severe heart failure or dehydration.
Allergic reactions, including swelling of the face, lips or throat (angioedema).
Liver inflammation, low red blood cell counts and other rare effects have been reported.
Heart rhythm problems, shortness of breath and sleep problems appear on lists of rare serious effects in consumer drug guides. Report any new, unusual symptoms to a clinician.
If you want to report a side effect to the FDA, you can use MedWatch.
The Pregnancy Boxed Warning
Losartan carries a boxed warning, the FDA's most serious warning, for fetal toxicity. Drugs that act directly on the renin-angiotensin system can injure or kill a developing baby. The prescribing information states that when pregnancy is detected, losartan should be stopped as soon as possible.
If you could become pregnant, talk to your doctor about contraception, and tell them straight away if you plan to become pregnant or think you may be. Do not stop losartan without medical advice, but do not delay that call either.
Important Interactions
Medicine or situation | Concern | What to do |
NSAIDs (ibuprofen, naproxen, diclofenac) | Can reduce losartan's effect and increase the risk of kidney problems | Ask your pharmacist; acetaminophen is usually preferred for pain |
Potassium supplements, salt substitutes, potassium-sparing diuretics (spironolactone, amiloride, triamterene) | Risk of dangerously high potassium | Avoid unless your doctor says otherwise; monitor potassium |
ACE inhibitors, other ARBs, or aliskiren | Dual blockade of the same system raises the risk of kidney problems, low blood pressure, fainting and high potassium | Generally avoided; aliskiren with losartan is contraindicated in people with diabetes |
Lithium | Levels can rise and become toxic | Needs close monitoring |
Diuretics and other blood pressure medicines | Added blood pressure lowering | Often used on purpose; stand up slowly and report dizziness |
Dehydration, vomiting, diarrhea, heavy sweating | Low blood pressure and kidney strain | Ask your doctor whether to pause losartan until you are drinking normally again |
Tell every clinician and pharmacist that you take losartan before starting any new medicine, including over-the-counter products and supplements.
Losartan Compared With Lisinopril and Amlodipine
Feature | Losartan (ARB) | Lisinopril (ACE inhibitor) | Amlodipine (calcium channel blocker) |
Typical daily dosing | Once daily | Once daily | Once daily |
Dry cough | Not typical | Common (about 1 in 10) | No |
Angioedema | Rare | Rare but more frequent than with ARBs | No |
Ankle swelling | Uncommon | Uncommon | Common |
Kidney protection in diabetes | Yes, approved for diabetic nephropathy | Yes, widely used | Not a main benefit |
Pregnancy | Contraindicated (boxed warning) | Contraindicated (boxed warning) | Not recommended without advice |
Potassium effect | Can raise potassium | Can raise potassium | Does not raise potassium |
Often chosen when | ACE inhibitor cough, or kidney protection is needed | First-line RAS blocker, heart failure, after heart attack | Black patients, older adults, angina, or when added to an ARB or ACE inhibitor |
Our guides on the other two: [Lisinopril (ACE Inhibitor) Complete Guide] and [Amlodipine (Norvasc) Complete Guide]
Monitoring and Day-to-Day Tips
Blood pressure: check at home if your doctor advises, and bring the log to visits.
Blood tests: your doctor will usually check kidney function and potassium when you start losartan, after dose changes, and periodically afterwards, particularly if you have diabetes or kidney disease.
Stand up slowly, particularly in the first weeks and after a dose increase.
Limit salt and avoid salt substitutes unless advised, because many contain potassium.
Stay hydrated, and ask what to do if you get a stomach bug.
Limit alcohol, which can add to dizziness.
Keep other risk factors in view: cholesterol, diabetes control, weight, activity and smoking. See: [High Blood Pressure (Hypertension): Complete Guide] and [Chronic Kidney Disease: Stages and Treatment Guide]
A note on recalls: in recent years, certain lots of losartan and other ARBs have been recalled because of impurities (nitrosamines) found during manufacturing. If your pharmacy contacts you about a recall, do not stop taking your medicine until you have spoken to your pharmacist or doctor, who can check the lot and arrange a replacement.
When to Get Medical Help
Seek emergency care for swelling of the lips, tongue, face or throat, difficulty breathing, fainting, chest pain, or a very slow or irregular heartbeat. Contact a clinician promptly for persistent dizziness, much less urine than usual, muscle weakness (which can signal high potassium), yellowing of the skin or eyes, or if you become pregnant.
The full US prescribing information for Cozaar is available at: https://www.drugs.com/pro/cozaar.html
The generic losartan prescribing information is available at: https://www.drugs.com/pro/losartan.html
A clinical summary of losartan's approved and off-label uses is available at: https://www.healio.com/clinical-guidance/drugs/cozaar
Frequently Asked Questions
What is losartan used for?
Losartan is used to treat high blood pressure, to reduce the risk of stroke in people with high blood pressure and a thickened left heart chamber (left ventricular hypertrophy), and to slow kidney damage in people with type 2 diabetes who have a history of high blood pressure, raised creatinine and protein in the urine. Doctors also use it off label in some people with heart failure or protein-leaking kidney disease.
How is losartan different from lisinopril?
Both lower blood pressure and protect the heart and kidneys, but they work at different points. Lisinopril is an ACE inhibitor and can cause a dry cough in a significant number of people because bradykinin builds up. Losartan blocks the angiotensin II receptor instead and does not typically cause cough, so it is a common switch for people who cannot tolerate an ACE inhibitor. Both carry a boxed warning for use in pregnancy and can raise potassium.
How long does losartan take to work?
It begins to lower blood pressure within hours, but the full effect usually takes several weeks, and doctors often review the dose after about 3 to 6 weeks. If your blood pressure is not at target, your doctor may raise the dose to 100 mg or add hydrochlorothiazide or another medicine.
What are the most important side effects and warnings?
The most important warning is the boxed warning against use in pregnancy. Other key risks are dizziness or fainting from low blood pressure, high potassium, worsening kidney function, and rarely swelling of the face or throat. NSAID pain relievers can weaken losartan and strain the kidneys, and aliskiren must not be combined with losartan in people with diabetes.
Can I stop taking losartan if my blood pressure is normal?
Do not stop on your own. Your blood pressure is normal because the medicine is working, and it will usually rise again if you stop. The prescribing information reports no withdrawal symptoms, but your doctor can decide whether a dose change or stopping is safe, particularly after lifestyle changes such as weight loss or less salt.
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