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Losartan: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on Aug 29, 2023.

1. How it works

  • Losartan may be used to treat high blood pressure or certain types of kidney disease.
  • Losartan works by blocking the effect of angiotensin II, a hormone that causes blood vessels to narrow (constrict) increasing blood pressure. Blocking angiotensin II widens (dilates) blood vessels which lowers blood pressure. Losartan also increases the excretion of certain salts from the kidney.
  • Losartan belongs to a group of medicines known as angiotensin II receptor blockers (which may be shortened to ARBs). Losartan may also be called an angiotensin II receptor antagonist.

2. Upsides

  • May be used to treat high blood pressure in adults and children over the age of six.
  • May be used to reduce the risk of stroke in people with high blood pressure and left ventricular hypertrophy, but this benefit may not apply to African-American people.
  • Lowering blood pressure has been shown to decrease the risk of fatal and nonfatal cardiovascular events (such as a heart attack or stroke).
  • May be used in the treatment of kidney disease in people with type 2 diabetes with a history of high blood pressure and elevated laboratory markers of creatinine and urinary protein.
  • May also be used to improve kidney outcomes in the general population (excluding African-American people) without kidney disease.
  • May be the preferred treatment in people with more than one type of heart condition.
  • Losartan tablets may be made into a suspension for people who have difficulty swallowing.
  • Available in three tablet strengths: 25mg, 50mg, and 100mg.
  • Losartan is available as a generic and as the brand name Cozaar.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Dizziness, nasal congestion, an infection in the upper airways (a cold), and back pain are the most commonly reported side effects. Diarrhea, tiredness, and low blood sugar have also been reported in people with type 2 diabetes taking losartan.
  • A persistent cough, although the risk of a cough is lower with losartan than with ACE inhibitors, such as captopril.
  • Rarely, may cause angioedema (this is a swelling of the deeper layers of the skin which can be life-threatening if it affects the throat).
  • May increase potassium levels in the body. Generally, should not be prescribed with potassium supplements or other medicines that retain potassium. Potassium levels may require ongoing monitoring.
  • Losartan may not have as good an effect in people of African-American descent.
  • The dosage of losartan may need to be reduced in people with liver disease.
  • Should not be used during pregnancy. Ensure adequate contraception is used when prescribing to women of childbearing age. If a woman inadvertently becomes pregnant while taking losartan, it should be immediately discontinued because medicines such as losartan can cause injury or death to the developing fetus.
  • May cause a significant drop in blood pressure in people who are dehydrated or salt-depleted when losartan is initiated. Dehydration or electrolyte imbalances should be corrected before the initiation of losartan.
  • There is a risk of acute kidney failure developing in people taking losartan. People whose renal function is dependent on the activity of the renin-angiotensin system (which includes the hormone angiotensin II), such as people with renal artery stenosis, chronic kidney disease, severe congestive heart failure, or who are dehydrated are more at risk. Renal function should be monitored periodically in these people. Losartan may need to be withheld or discontinued in people who develop a significant decrease in kidney function.
  • May interact with several other drugs including NSAIDs, lithium, and potassium supplements. Losartan should never be administered with aliskiren.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Losartan works on a hormone called angiotensin II to lower blood pressure and may also improve kidney function in some people. People being initiated on losartan should be adequately rehydrated and have normal electrolyte levels.

5. Tips

  • Can be administered with or without food.
  • Ensure you are adequately hydrated before starting this medicine.
  • The dosage of losartan may need adjusting depending on how you respond to it.
  • May be administered with other drugs that are also used to lower blood pressure (such as diuretics).
  • Losartan may cause a drop in blood pressure, especially when going from a sitting or lying down position to standing. This may make you feel dizzy and increase your risk of falling over. Talk to your doctor if this happens to you.
  • if you develop swelling in your feet, ankles, or hands, or unexplained weight gain contact your doctor as it may be a sign that your kidneys not working as well.
  • Losartan suspension can be refrigerated for up to 4 weeks.
  • Your doctor may require you to see him or her regularly for monitoring of your blood pressure, kidney function, or electrolytes.
  • If you are a woman capable of having children, you should ensure you use adequate contraception to avoid getting pregnant while on losartan, as it can be harmful to a developing baby. If you do inadvertently become pregnant, tell your doctor immediately.
  • Do not take potassium supplements or other supplements that contain potassium with losartan unless your doctor has advised you to do so.

6. Response and effectiveness

  • Losartan is metabolized in the liver to an active metabolite (which has a similar action to losartan). The time to peak effect after a dose is 1-2 hours for losartan and 3-4 hours for the metabolite. At its peak level, losartan inhibits 85% of the effects of angiotensin II, and 25 to 40% of this inhibition persists for 24 hours. It may take up to a week for significant blood pressure-lowering or kidney effects to be noted, with maximal effects occurring in 3 to 6 weeks. No rebound effect has been noted when losartan is discontinued.
  • May not be as effective in people of African-American descent.
  • The effects of losartan may be enhanced in people who are dehydrated.

7. Interactions

Medicines that interact with losartan may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with losartan. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with losartan include:

  • aliskiren
  • amifostine
  • anticonvulsants, such as phenobarbital
  • antifungal agents such as fluconazole
  • antipsychotic agents (may enhance the blood pressure-lowering effect), such as aripiprazole or clozapine
  • aspirin
  • azathioprine
  • bupropion
  • cyclosporine
  • diuretics, such as amiloride
  • heparin
  • levodopa
  • lithium
  • NSAIDs, such as ibuprofen, diclofenac, or naproxen
  • other ARBs (such as candesartan or irbesartan) or ACE inhibitors (such as captopril or lisinopril)
  • phosphodiesterase-5-inhibitors, such as sildenafil
  • potassium supplements
  • sedatives, such as temazepam and zolpidem
  • trimethoprim.

Losartan may also cause blood sugar levels to drop more than expected when taken with diabetes medication, including insulin. Increased blood sugar monitoring may be required.

Note that this list is not all-inclusive and includes only common medications that may interact with losartan. You should refer to the prescribing information for losartan for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use losartan only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: August 29, 2023.