Losartan

2 medicines

Losartan is an angiotensin receptor blocker (ARB) for high blood pressure; it must not be taken during pregnancy because it can seriously harm or kill an unborn baby's kidneys.

Cozaar

Losartan

25/50/100mg

Cozaar is a heart blood pressure medication containing Losartan, available as 25/50/100mg tablets.

from $0.54 / tablet View

Hyzaar

Losartan, Hydrochlorothiazide

12.5mg

Hyzaar is a heart blood pressure medication containing Losartan + Hydrochlorothiazide, available as 12.5mg tablets.

from $0.66 / tablet View

Key facts

  • Losartan is an angiotensin II receptor blocker (ARB). It relaxes blood vessels to lower blood pressure and is also used to protect the heart and kidneys in some conditions.
  • It is taken once or twice daily by mouth; it can take 3 to 6 weeks of steady use for the full blood-pressure-lowering effect to show.
  • Losartan must not be taken during pregnancy. Like other drugs that block this hormone system, it can injure or kill a developing baby's kidneys, especially from the second trimester onward, so stop it and tell your doctor immediately if you become pregnant or are planning to.
  • Seek urgent care for sudden facial or throat swelling, fainting, or signs of very high blood potassium such as muscle weakness or an irregular heartbeat.

What Losartan treats

Losartan treats high blood pressure and lowers the risk of stroke in people with high blood pressure and thickening of the heart's left chamber. It is also used in heart failure and to slow kidney damage in people with type 2 diabetes who have protein in their urine. It does not treat a hypertensive emergency and is not a painkiller.

How Losartan works

A hormone called angiotensin II normally attaches to receptors on blood vessels, making them narrow and raising blood pressure. Losartan blocks these receptors, so angiotensin II cannot act on the vessels. This lets the vessels relax and widen, lowering blood pressure and reducing the workload on the heart.

Before you take it

  • Do not take losartan if you are pregnant, and stop it as soon as pregnancy is confirmed. It is not recommended in breastfeeding either.
  • Avoid combining it with a medicine containing aliskiren if you have diabetes or kidney disease.
  • Tell your prescriber about potassium supplements, salt substitutes, potassium-sparing diuretics, and regular NSAID use, since these can raise blood potassium.
  • Mention any history of narrowed kidney arteries, severe liver disease, or dehydration before starting.

Side effects

Common effects include dizziness, tiredness, mild muscle cramps, and stomach upset, particularly when starting treatment.

Seek urgent care for:

  • Swelling of the face, lips, tongue or throat, or sudden difficulty breathing.
  • Fainting or a severe drop in blood pressure.
  • Signs of high potassium, such as numbness, tingling, muscle weakness, or an irregular heartbeat.
  • A marked drop in how much urine you pass.

Safety essentials

  • Losartan is contraindicated in pregnancy: confirm you are not pregnant before starting, use reliable contraception if pregnancy is possible, and switch to a doctor-approved alternative if you are planning a pregnancy.
  • Blood tests for kidney function and potassium are usually checked before starting and periodically afterward, since losartan can raise potassium, particularly alongside other potassium-raising drugs or in kidney disease.
  • Stay hydrated and tell your doctor before any illness causing vomiting or diarrhea, since dehydration can drop your blood pressure further or affect your kidneys while on losartan.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.