Losartan (ARB): everything you need to know

Losartan belongs to a class of medications called angiotensin II receptor blockers (ARBs). It is commonly used to treat high blood pressure and is sometimes combined with other medicines, like hydrochlorothiazide.

Angiotensin II receptor blockers (ARB) work on the renin-angiotensin system, a complex interplay of compounds affecting the blood vessels, heart, and kidneys—this system regulates blood pressure. Angiotensin II plays a vital role in this system because it causes blood vessels to constrict (squeeze)—over time, this can lead to hypertension. By blocking the angiotensin II receptor, losartan prevents this constriction and lowers blood pressure (DailyMed, 2020).

Losartan is related to another class of blood pressure medications, the angiotensin-converting-enzyme (ACE) inhibitors. Examples of ACE inhibitors include lisinopril and enalapril. Both losartan and ACE inhibitors act on the renin-angiotensin system to lower blood pressure. However, they interfere with different parts of the process and have other side effects. Some people who do not tolerate ACE inhibitors (because of coughing or swelling of tissues) may use losartan instead.

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Losartan is FDA-approved to treat the following conditions (DailyMed, 2020):

• High blood pressure (hypertension)

• Stroke risk

• Kidney problems from diabetes (diabetic nephropathy)

High blood pressure (hypertension)

The Centers for Disease Control and Prevention (CDC) estimates that almost half of all adults in the United States have high blood pressure (CDC, 2020). This condition can affect your blood vessels, heart, brain, kidneys, and other body parts. High blood pressure, or hypertension, can also lead to heart attacks and heart failure. Treating hypertension can decrease your risk of stroke and heart attacks. If you have high blood pressure, your healthcare provider may recommend taking losartan (brand name Cozaar) in addition to lifestyle changes like a healthy diet, regular physical activity, and smoking cessation.

Stroke

People with high blood pressure are at an increased risk of having heart attacks and strokes. Continually trying to pump blood against the elevated pressure in your blood vessels takes a toll on the heart. Some people develop an enlarged heart in response to chronic high blood pressure, especially on the left side of the heart—this side pumps blood to the aorta and the rest of the body. This heart enlargement, called left ventricular hypertrophy, indicates that your heart is struggling because of the elevated blood pressure.

Using losartan in people with high blood pressure and left ventricular hypertrophy can decrease their risk of stroke. It is important to note that in clinical studies, this medication did not seem to be as effective at reducing the risk of strokes in Black people (DailyMed, 2020).

Kidney problems from diabetes (diabetic nephropathy)

Diabetes can wreak havoc on your body—it can affect your eyes, nerves, blood vessels, and kidneys, among other things. It is a significant contributor to chronic kidney disease and end-stage renal failure. The high level of sugars in your blood damage the kidneys’ filtering system, causing them to leak protein into the urine and lose the ability to filter out waste products (ADA, n.d.). The risk of kidney disease in diabetes increases if you also have high blood pressure.

Losartan can help people with type 2 diabetes and hypertension not only lower their blood pressure but also slow the progression of their kidney disease. Treatment may help you avoid serious complications like kidney failure, which may require dialysis or a kidney transplant.

Off-label

Losartan is also prescribed for several "off-label" uses. "Off-label" means that the drug is being used to treat conditions that it was not specifically FDA-approved to treat. Some of the "off-label" uses for losartan include (UpToDate, n.d.):

• Heart attack: Losartan may be used after a heart attack, often in combination with other drugs.

• Heart failure: In heart failure, your heart is not healthy enough to adequately pump blood throughout your body. Losartan may help, especially in people who cannot tolerate angiotensin-converting enzyme (ACE) inhibitors.

• Marfan's syndrome with aortic aneurysm: Marfan's syndrome is an inherited condition that affects your connective tissue, like eyes, blood vessels, etc. Sometimes people with Marfan's syndrome develop a balloon-like outpouching of the aorta (the largest artery), which is potentially life-threatening. Treating with losartan can help decrease the likelihood of aneurysm rupture.

• Non-diabetic kidney disease: While it is FDA-approved to help with diabetic nephropathy, losartan may also help with non-diabetic kidney disease.

Side effects of losartan

Losartan is an effective ant-hypertensive agent, and it is generally well-tolerated. However, like all drugs, there are side effects.

Losartan has a ”black box" warning, a serious advisory from the FDA regarding severe side effects: Do not take losartan if you are pregnant. If you become pregnant while taking it, stop losartan immediately. It can cause injury or death to the fetus if taken during the last six months of pregnancy (Medline Plus, 2018).

Common side effects include (DailyMed, 2020):

• Dizziness

• Upper respiratory infection (e.g., the common cold)

• Nasal congestion

• Back pain

• Persistent dry cough

• High potassium levels in the blood (hyperkalemia)

• Muscle aches

• Rash

• Diarrhea

• Decreased sensitivity to touch

Serious side effects include (UpToDate, n.d.):

• Severe allergic reaction with hives, itching, rash, trouble breathing, etc.

• Low blood pressure, especially in people with dehydration

• Changes in kidney function

This list does not include all possible side effects and others may exist. Check with your pharmacist or healthcare provider for more information.

Potential drug interactions

Inform your healthcare provider about any other medications you may be taking before starting losartan to prevent potential drug interactions, which include (DailyMed, 2020):

• Drugs that increase potassium levels: Since losartan can increase your potassium levels, combining it with other medicines that also raise potassium can lead to higher than normal amounts of potassium in your body. Very high concentrations may cause chest pain, irregular heartbeats, nausea/vomiting, and weakness. Potassium-sparing diuretics are also used in the treatment of high blood pressure; examples include amiloride and spironolactone. Also, you should not take potassium supplements with losartan without checking with your healthcare provider. Salt substitutes are another potential source of potassium because they often use potassium chloride (instead of sodium chloride)—tell your healthcare provider if you use these.

• Lithium: Lithium is a mood stabilizer often used to treat bipolar disorder. Combining lithium with losartan can lead to higher levels of lithium and increases the risk of lithium toxicity.

• Non-steroidal anti-inflammatory (NSAIDs) drugs: These drugs are often used to treat inflammation; examples include ibuprofen and naproxen. However, if you take NSAIDs with losartan, you run the risk of worsening kidney function. This is especially true in people who already have compromised kidney function. Also, NSAIDs can decrease losartan's ability to lower blood pressure.

• ACE inhibitors: ACE inhibitors, like losartan, act on the renin-angiotensin system. However, even though they also lower blood pressure, they affect a different part of the system. Using losartan along with ACE inhibitors (like lisinopril and enalapril) raises the risk of side effects like low blood pressure (hypotension), fainting (syncope), high potassium levels (hyperkalemia), and worsening kidney function (or even kidney failure). Aliskiren, a renin inhibitor, is another drug that acts on the renin-angiotensin system—combining it with losartan also increases the chances of the listed side effects, including kidney failure. In general, you should not combine losartan with other medications that also act on the renin-angiotensin system.

This list does not include all possible drug interactions with losartan and others may exist. Check with your pharmacist or healthcare provider for more information.

For any number of reasons, certain groups of people should not take losartan or use it with caution. These groups include (DailyMed, 2020):

• Pregnant women: Black box warning from FDA- Pregnant women should not take losartan. If you become pregnant while taking it, stop losartan immediately as it can cause injury or death to the fetus if taken during the last six months of pregnancy.

• Women who are breastfeeding: Nursing mothers should consult with their healthcare provider. The decision to take losartan involves weighing the risks to the baby with the benefits to the mother.

• Black people: Losartan may not be as effective at reducing the risk of stroke in Black people with high blood pressure and left ventricular hypertrophy (enlarged heart) as effectively as in other populations. If reducing stroke risk is your goal, talk to your healthcare provider about other options.

• Children under six: Losartan's safety and effectiveness in children under six years of age with high blood pressure have not been studied.

• People with abnormal liver function: Since the liver breaks down losartan, people with decreased liver function may have higher than expected levels of losartan (up to five times higher). Your healthcare provider may need to adjust your losartan dose, especially in severe cases of liver issues.

• People with renal artery stenosis: If you have renal artery stenosis, a narrowing of the artery to your kidney, you risk worsening kidney function with losartan.

This list does not include all at-risk groups. Talk to your healthcare provider or pharmacist for more information. 

Losartan is available both as generic losartan potassium tablets and as brand name Cozaar. Tablets are available in 25 mg, 50 mg, and 100 mg strengths. Most people usually take one pill daily. Try to take losartan around the same time every day for the best results. Sometimes your provider may start you on a lower dose and then gradually increase the medicine strength.

Most insurance plans cover losartan. The cost of a 30-day supply ranges from around $8–$10 (GoodRx.com).

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Current version

August 25, 2020

Written by

Chimene Richa, MD

Fact checked by

Mike Bohl, MD, MPH, ALM

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About the medical reviewer

Mike Bohl, MD, MPH, ALM

Dr. Mike is a licensed physician and a former Director, Medical Content & Education at Ro.