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Losartan: what it is used for and what to know
Losartan is a prescription medicine in the ARB class that lowers high blood pressure; Cozaar was its original brand name. Per the FDA label, it is used to treat hypertension in adults and in children 6 and older, and to help protect the kidneys in some people with type 2 diabetes. It is not a controlled substance. It is not taken during pregnancy. In a video visit, the doctor reviews your readings and evaluates whether it is right for you.
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Is this an emergency?
This is not an emergency service. Call 911 or go to the nearest emergency room if you have:
- Swelling of the face, lips, tongue or throat, or trouble breathing or swallowing (angioedema or an allergic reaction)
- Fainting, severe dizziness on standing, or very low blood pressure
- Chest pain, shortness of breath, weakness on one side of the body, trouble speaking or vision changes
- An irregular heartbeat, marked muscle weakness or strong tingling (possible signs of high potassium)
- Vomiting or diarrhea that will not stop and keeps you from drinking fluids, or very little urine
- Confirmed or suspected pregnancy while taking losartan: call the doctor the same day and do not keep taking it without talking to her
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What is losartan?
Losartan (losartan potassium) is an oral medicine in the angiotensin II receptor blocker (ARB) class. It requires a prescription and is not a controlled substance: its FDA label lists no DEA schedule. It comes as 25, 50 and 100 mg tablets, and also combined with hydrochlorothiazide (a water pill) in a single tablet.
How it works. According to MedlinePlus, angiotensin II is a substance in the body that tightens blood vessels. Losartan blocks it, so the vessels relax and blood flows more easily. It controls blood pressure but does not cure hypertension, which is why you keep taking it even when you feel well.
Losartan and Cozaar: are they the same?
Yes. Cozaar is losartan's original brand name; the generic has the same active ingredient. The combination with hydrochlorothiazide was sold under the brand Hyzaar. If your prescription or bottle says "losartan potassium," that is losartan.
What is losartan used for?
According to the FDA label, losartan is approved to:
- Treat [high blood pressure](route:condition-high-blood-pressure) (hypertension) in adults and in children 6 and older, alone or with other medicines. Lowering blood pressure reduces the risk of stroke, heart attack and kidney problems.
- Reduce the risk of stroke in adults with hypertension and thickening of the left ventricle of the heart. The label notes this benefit may not apply to Black patients.
- Help protect the kidneys in adults with type 2 diabetes, high blood pressure, raised creatinine and protein in the urine (diabetic nephropathy).
How losartan is taken: what the label says
Adults with high blood pressure. Per the FDA label, the usual starting dose is 50 mg once a day, and the usual range is 25 to 100 mg a day in one or two doses. If a person is dehydrated or on high-dose water pills, or has liver problems, a 25 mg start is typical.
Children 6 and older. The dose is based on weight (0.7 mg per kilogram once a day, up to a maximum of 50 mg). It is not recommended under age 6 or in children with very low kidney filtration.
With or without food. It can be taken with or without food, and it works best taken at the same time every day. According to MedlinePlus, the full effect can take a few weeks, so do not stop if you do not notice a change: high blood pressure rarely causes symptoms.
If you miss a dose, take it when you remember unless it is almost time for the next one. Do not take two doses together.
The doctor decides the dose, based on your blood pressure readings, your kidneys, your other conditions and how well you tolerate the medicine. Do not change or stop it on your own.
Losartan side effects
According to the FDA label and MedlinePlus, the most common losartan side effects are:
- Dizziness, especially when standing up quickly
- Nasal congestion or mild upper respiratory infections
- Back pain
- Diarrhea
- Tiredness
- Headache
How to manage dizziness
Dizziness happens because blood pressure drops. It can usually be managed with simple steps, and dizziness that keeps happening is a reason to talk with the doctor (dizziness):
- Stand up slowly from bed or a chair.
- Drink enough fluids, especially on very hot days.
- Expect the first days. It is more common when you start or raise the dose.
- Check your blood pressure at home and write down the readings for the visit; they help the doctor adjust treatment.
- If you faint or a reading comes out very low, get care; do not stop the medicine without talking to the doctor.
FDA boxed warning: pregnancy
The losartan label carries a boxed warning about fetal toxicity: medicines that act on this system can cause serious injury or death to a developing baby when used in pregnancy, especially in the second and third trimesters. Per the label, when a pregnancy is detected, losartan should be stopped as soon as possible.
If you are pregnant, planning to be, or could become pregnant and do not use reliable birth control, tell the doctor. She can choose a different blood pressure medicine that fits your situation. If you find out you are pregnant, call the doctor the same day and do not leave your blood pressure untreated on your own. If you breastfeed, tell her too: the label advises deciding with your doctor based on your situation.
Losartan, potassium and your kidneys
Losartan can raise the potassium level in your blood and change kidney function, especially if you already have kidney disease, are dehydrated, or take other medicines that affect the kidneys. That is why the doctor may order blood tests (creatinine and potassium) when you start, when the dose changes and periodically.
- Avoid potassium supplements and potassium-based salt substitutes unless the doctor tells you otherwise.
- If you are vomiting or have diarrhea, tell the doctor: dehydration affects the kidneys. The medicine is sometimes paused for a few days; that decision is hers.
- People with narrowed arteries to the kidneys can have marked changes in kidney function with this type of medicine.
- If your lab showed high creatinine, the doctor reviews your case. See how to read your lab results.
Losartan interactions and when it is not used
Before starting, tell the doctor and the pharmacist everything you take, including supplements. Per the FDA label:
- It is not used if you are allergic to losartan or any of its ingredients. It is also not combined with aliskiren in people with diabetes.
- Anti-inflammatory pain relievers such as ibuprofen and naproxen (NSAIDs): they can reduce losartan's effect and worsen kidney function, especially in older adults or when dehydrated. Ask the doctor what to use for pain.
- Other medicines in the same system (ACE inhibitors such as lisinopril): combining them with losartan raises the risk of high potassium, low blood pressure and kidney injury. They are not taken together without medical direction.
- Water pills and potassium supplements: they can change potassium and fluid balance.
- Lithium: losartan can raise its blood level.
- Rifampin and fluconazole can change how much active losartan reaches the blood.
- Alcohol: it can lower blood pressure further and increase dizziness.
Losartan, cough and swelling
ARBs such as losartan cause a dry cough less often than ACE inhibitors do. Sudden swelling of the face, lips, tongue or throat (angioedema) is rare but serious: it is an emergency, so call 911. If you had angioedema with another blood pressure medicine, tell the doctor.
How long do you take losartan?
High blood pressure is usually a long-term condition. Stopping losartan suddenly can let your pressure rise again, and uncontrolled blood pressure raises the risk of stroke, heart attack and kidney failure. The doctor reviews your readings, your lab results and your side effects at each visit to decide whether to continue the same dose, adjust it or change medicines. Lifestyle changes (less salt, physical activity, a healthy weight) remain part of the plan, as the ACC/AHA blood pressure guideline explains.
Book an evaluation
Book an evaluation; the doctor decides whether a treatment is right for you.
You see Dr. Diana Nieves Castro, MD, a Puerto Rico–licensed general practice physician, in English or Spanish. She can review your blood pressure readings, your symptoms and your medicines, give you a lab order and, if appropriate, adjust or change your treatment and follow up with you. Every day, any time (Puerto Rico time). Doctor online 24/7: video doctor visits 24/7. See chronic condition care and how an online doctor visit works.
Already taking losartan? If you need to continue a medicine you already take (non-controlled), see prescription refills: the doctor reviews how you are doing and decides whether a refill or an adjustment is appropriate.
The pharmacy bills for the medicine. We do not bill insurance; on request we give you an itemized receipt (superbill). Visits are private and not recorded. See pricing and book your visit.
How we care for you
We evaluate, diagnose and treat; if needed, we give you a lab order for a lab near you.
We see adults and children of all ages. Patients under 21: a parent with patria potestad (parental authority) or a legal guardian is on camera for the whole visit and shows photo ID.
Real-time video visit. We send you a secure video link. It works on your phone, tablet or computer.
If appropriate, the doctor prescribes and we send your prescription to your pharmacy.
You must be physically in Puerto Rico during the visit (visitors, tourists and cruise passengers are welcome).
In an emergency, call 911.
Frequently asked questions
Can I get losartan renewed or my blood pressure reviewed by video?
What do losartan 25 mg, 50 mg and 100 mg mean?
Should losartan be taken in the morning or at night?
How long does losartan take to work?
Can you take losartan during pregnancy?
Can I take ibuprofen with losartan?
Does losartan cause a cough like other blood pressure pills?
What should I do if I have vomiting or diarrhea while taking losartan?
About this page
Author: The Health Initiative
Medical care provided by Dr. Diana Nieves Castro, MD (PR license 24027)
Disclosure: Founding Executive Director of The Health Initiative
Published: 2026-10-10 · Updated: 2026-10-11
Sources (4)
- DailyMed (NLM): Losartan potassium tablets, FDA label (opens in a new tab) (accessed 2026-10-10)
- MedlinePlus: Losartan (opens in a new tab) (accessed 2026-10-10)
- MedlinePlus (Spanish): Losartán (opens in a new tab) (accessed 2026-10-10)
- 2017 ACC/AHA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults (Hypertension 2018;71) (opens in a new tab) (accessed 2026-10-10)