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Medically Approved

How does losartan work?

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What it doesHow much it helpsHow to takeHow soon it worksSide effectsDoes it cure hypertension?Alternative medsSummary
Losartan lowers blood pressure by blocking the action of a natural enzyme in the body. This relaxes and widens blood vessels, making it easier for the heart to pump blood.
Medically reviewed by Alyssa Walton, PharmD
Updated on October 27, 2023

Losartan potassium is a generic medication that belongs to the angiotensin II receptor blockers (ARB) drug class. You can find it in the United States under the brand name Cozaar.

Standard or ideal blood pressure for adults is 120/80. The top number is your systolic blood pressure (when the heart contracts), while the bottom one measures diastolic blood pressure (when your heart is at rest).

When your blood pressure is persistently higher than that, your healthcare professional may recommend a medication such as losartan.

Losartan is available by prescription only and in oral form.

Need a refill for losartan (Cozaar)? You may be able to get an online prescription through Optum Perks in as little as 15 minutes with no video or appointment needed. Learn more here.

What losartan potassium does to your body

Adult male taking his blood pressure after taking losartan
Photography by AsiaVision/Getty Images

Blood pressure is the force of blood as it pushes against your blood vessels, leading to and from the heart. The narrower the vessel, the higher the pressure against its walls. When your blood pressure is constantly high, those blood vessels can become less flexible over time.

Losartan potassium works by blocking angiotensin. That’s a chemical in the body that causes blood vessels to narrow.

Angiotensin itself needs a slot, or a receptor, to fit into to make the arteries tighten. Losartan potassium and other ARB medications block those slots or receptors so that angiotensin can’t attach to them and narrow your blood vessels.

As a result of taking losartan, your blood vessels stay relaxed and wide, and your blood pressure lowers as a consequence.

Your healthcare professional may recommend losartan potassium if your blood pressure is consistently above 130/80, which is considered stage 1 hypertension. They may also prescribe it for other reasons, including to:

  • lower the risk of a stroke if you have high blood pressure or an enlarged heart
  • treat kidney problems if you have type 2 diabetes and high blood pressure

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How much does losartan lower blood pressure?

Recent evidence on how much blood pressure lowers with losartan is limited.

A 1995 study of non-Black adult men and women with mild hypertension notes that, within a 24-hour period, all doses of losartan:

  • lowered systolic blood pressure (the top number) between 9.4 and 14.2 mmHg
  • lowered diastolic blood pressure (the bottom number) between 5.6 and 9.0 mmHg

A 2002 study of 380 adults with high systolic blood pressure (140–200 mmHg) also noted that taking losartan once per day reduced the readings between 8.4 and 14.8 mmHg over 12 weeks of treatment.

Larger and more comprehensive research is needed to determine how much losartan may lower blood pressure in different populations and for other diagnoses.

How to take losartan potassium

Losartan and Cozaar come in tablets that you swallow. Usually, you take it once or twice per day, depending on your symptoms. If you take it once per day, your healthcare professional may recommend you do so at night.

You may start on a low dose, like 25 or 50 milligrams (mg) a day. Then, the dose may rise as needed. The maximum daily losartan dose you can take is 100 mg.

Your initial and maintenance dose may depend on what you take losartan for.

How long does losartan take to work?

Your blood pressure may lower during the first few hours after you take losartan. But it may take up to 6 weeks for you to experience the medication’s full therapeutic effects.

If your blood pressure doesn’t reach the target level (usually 120/80 or under), your healthcare team may increase your dose or add other medications to your plan. It is also possible they replace losartan with another blood pressure medication.

What are the side effects of losartan?

Losartan potassium may not cause as many side effects as other blood pressure medications. Still, some adverse effects are possible, including:

  • back pain
  • nose congestion
  • lightheadedness
  • respiratory infections
  • stomachaches
  • sleep disturbances
  • muscular pain

Serious but rare side effects of losartan may include:

  • erectile dysfunction
  • chest pain and heart palpitations
  • increased potassium levels
  • depression

Losartan isn’t indicated during pregnancy as it may cause serious development and safety issues for the fetus.

Can losartan potassium cure my high blood pressure?

No medication “cures” high blood pressure. But drugs such as losartan may help you manage it and reduce the chance of complications.

Besides pharmaceutical treatment, your healthcare professional may also recommend you consider lifestyle strategies, including:

  • weight management
  • reduced salt intake
  • nutrient-dense diets
  • regular physical activity

Alternative medications to losartan

If losartan isn’t working well enough to lower your blood pressure, your healthcare professional may switch you to one or more of these medications:

Download the free Optum Perks Discount Card to save up to 80% on some prescription medications.


Losartan works by blocking the action of a substance in your body that tightens and narrows blood vessels. As the medication acts on your body, blood vessels relax and help to lower blood pressure.

You may experience the full therapeutic effects of losartan in about 6 weeks, although the drug starts having an effect as soon as you take it.

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