Losartan potassium is a medication that doctors prescribe to treat high blood pressure or hypertension.

Losartan potassium works by relaxing the blood vessels to allow the blood to flow more efficiently, which reduces a person’s blood pressure. The United States Food and Drug Administration (FDA) approved the drug in 1995 to treat hypertension.

The World Health Organization (WHO) include losartan potassium on their list of essential medicines, which catalogs the most effective and safe medications that experts consider necessary in a healthcare system.

People should not use this medication while pregnant.

This article provides an overview of losartan potassium, including its uses, side effects, potential drug interactions, and other warnings.

What is losartan potassium used for?

man taking medication while working at desk
A doctor may prescribe losartan potassium to treat high blood pressure.

Losartan potassium is a type of angiotensin receptor blocker (ARB) known by the brand name Cozaar. Doctors prescribe it to treat hypertension and nephropathy, which is damage to the kidneys, in people with type 2 diabetes.

Doctors most commonly prescribe losartan potassium to treat hypertension in adults and children over 6 years of age.

For many people, lifestyle changes, such as diet, exercise, and avoiding smoking and alcohol, are sufficient to reduce blood pressure to healthy levels. Others may need medication to control their blood pressure.

Untreated high blood pressure can have serious health consequences. Reducing high blood pressure protects against some related health conditions, including:

Medications such as losartan potassium are just one aspect of hypertension treatment. Others include lifestyle and dietary changes. Sometimes, individuals will take losartan alongside other medicines, including diuretics, to control their high blood pressure.

People with diabetes may take losartan to protect their kidneys from damage that occurs as the result of the disease, such as diabetic nephropathy.

How effective is losartan potassium?

The WHO consider losartan as safe, effective, and necessary in a health system. Many research studies also report that the medication is both safe and effective for a variety of uses.

A 2010 research paper, which reviewed the previous 15 years of losartan use, reports that the drug is beneficial for:

  • controlling hypertension
  • decreasing stroke risk
  • reducing proteinuria, which is an abnormal amount of protein in the urine that suggests kidney damage
  • slowing diabetic nephropathy

The research also states that losartan potassium has other positive effects, including:

  • decreased uric acid levels: uric acid contributes to the development of gout
  • reduced platelet aggregation: platelet aggregation increases blood clot risk
  • regression of left ventricular hypertrophy: enlargement of the heart’s left ventricle, which raises the risk of heart problems

Losartan potassium can cause dizziness, but it produces few other side effects. A 2015 study suggests that losartan has a lower incidence of side effects yet is just as effective as other drugs for hypertension.

This medication is also effective in young people. A meta-analysis from 2018 looked at the effects of losartan potassium in children and adolescents, with a median age of 12, whose hypertension had not improved through lifestyle changes. They found that the treatment reduced blood pressure more than a placebo.

Side effects

woman driving
A person should not drive if taking losartan potassium causes dizziness.

Dizziness is a common side effect of losartan. This usually affects people who are just beginning treatment, as their bodies are adjusting to the drug.

Other side effects include:

  • upper respiratory infection
  • nasal congestion
  • back pain

To prevent dizziness or associated injuries, doctors advise people to change positions slowly. For example, carefully move from a lying position to a sitting one, and from a seated position to an upright one.

Avoid driving or using heavy machinery while dizzy. See a doctor if dizziness or lightheadedness persists or gets worse.

Most people do not experience serious adverse reactions to losartan potassium.

If serious side effects do occur, seek urgent medical attention. These include:

  • chest pain
  • fainting
  • irregular heartbeat or palpitations
  • muscle weakness
  • unusual changes in the amount of urine output
  • vomiting

Call 911 or go to the nearest emergency department if symptoms of an allergic reaction to the drug occur. Allergy symptoms include:

  • breathing difficulties
  • itching
  • loss of consciousness
  • rash
  • severe dizziness
  • swelling of the face, tongue, or throat

Allergic reactions to losartan are rare.

Losartan potassium warnings

Losartan potassium is not suitable for everyone. People with hypertension should consider and talk to a doctor about the following factors before taking losartan potassium:

Drug allergies

People who are allergic to losartan potassium or other inactive ingredients in the drug should avoid it. Inactive ingredients in Cozaar are:

  • hydroxypropyl cellulose
  • hypromellose
  • anhydrous lactose
  • magnesium stearate
  • microcrystalline cellulose
  • cornstarch
  • titanium dioxide

Inform a doctor or pharmacist of all drug allergies before taking losartan.

Pregnancy, trying to conceive, or breast-feeding

Losartan and similar medicines can affect a fetus. They may affect the kidney function of the fetus and increase their risk of illness or death.

People taking losartan should speak to their doctor immediately after confirming the pregnancy, as they will likely need to stop taking the medication until the baby is born.

The FDA advise that people who breast-feed should not take losartan, as they do not know whether or not the medication passes into the breast milk.

Medical conditions or symptoms

People who have any of the following conditions should speak to their doctor before taking losartan:

Drug interactions

Losartan potassium can interact with some drugs and supplements. People should give their doctor a complete list of the prescription medications, non-prescription medications, vitamins, and supplements they take.

Among others, losartan may interact with:

How to take losartan potassium and dosage

packets of medication in pharmacy
The dosage for losartan potassium can vary, and people should take it as prescribed.

Losartan potassium, sold as Cozaar, is available in tablet form in three doses:

  • 25 milligrams (mg)
  • 50 mg
  • 100 mg

The dosage of losartan a person will take will depend on several factors. Their doctor will prescribe the necessary dose for their age, weight, condition, and overall health.

General guidelines for losartan potassium dosage are as follows:

  • Hypertension. Typically, people will take 50 mg once a day, although some individuals may require 100 mg daily. A doctor may prescribe other hypertension drugs or diuretics in addition to losartan.
  • Nephropathy in people with type 2 diabetes. People with diabetes typically begin on 50 mg daily, which may increase to 100 mg daily depending on their reaction to the drug.
  • Hypertension in people with left ventricular hypertrophy. The starting dose is usually 50 mg, and this may increase to 100 mg daily.
  • Hypertension in children. Children aged 6 and over may begin on a very low dose. Rarely, they may require up to 50 mg of losartan per day, depending on their blood pressure response.

Always take losartan exactly as a doctor prescribes. Swallow the tablet with a glass of water, with or without food. Take missed doses as soon as possible, but do not take 2 doses close together. Only take one dose at a time.

A losartan overdose that causes severe symptoms requires emergency medical attention. Call 911 right away. For less severe symptoms, call the American Association of Poison Control Centers at 1-800-222-1222.


Losartan potassium is a hypertension treatment. Research suggests that the medication is safe and effective for most people. People may experience mild side effects, such as dizziness, in the early stages of treatment.

People who experience severe or persistent side effects should contact their doctor right away. Seek emergency medical attention for symptoms that affect breathing or cause swelling of the mouth or throat.

To reduce blood pressure and avoid complications, always take losartan according to a doctor’s instructions. Be sure to discuss any concerns about losartan or its effects with a medical professional.