Avoid high blood pressure with Losartan (generic Cozaar and Hyzaar)

Losartan (losartan potassium) is a widely used prescription-only treatment for high blood pressure that’s been around in the US market for 25 years.

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Written by Dr Kim Langdon, MD

Information last reviewed 07/15/19


What is Losartan?

Losartan (Cozaar generic), is from the category of drugs known as ‘angiotensin II receptor antagonists’ and is used to treat high blood pressure. Its onset of action is relatively fast and it works by multiple mechanisms. Angiotensin is a protein secreted by the kidney which is changed into other substances that cause the blood vessels to constrict, raising blood pressure. Under normal circumstances, this process is under control and results in normal blood pressure. When it is overactive or dysfunctional, high blood pressure can occur.

Losartan potassium is not the same thing as losartan potassium-hydrochlorothiazide (Hyzaar) which also has a diuretic effect when combined with the hydrochlorothiazide.

How does Losartan work?

Cozaar (losartan potassium) works to relieve high blood pressure in five ways;

  1. Losartan binds to the angiotensin 1 receptor and inhibits it, which helps the vessels to dilate and lowers blood pressure.
  2. Cozaar blocks the action of angiotensin-2, which is another potent blood vessel constrictor.
  3. Aldosterone and adrenaline hormones are also reduced. Adrenaline is the ‘fight or flight’ hormone that raises pulse and blood pressure. Aldosterone causes the retention of salt and water, which leads to elevated blood pressure.  
  4. Salt (sodium) and water are released out of the body through the urine, all of which lowers blood pressure.
  5. Losartan also promotes the growth of heart muscle and blood vessels.

How long does Losartan take to work?

Losartan starts working about 6 hours after it is taken

How effective is Losartan?

It is not possible to quantify how effective Losartan is, however, it is generally quite effective at treating high blood pressure. In addition, it is effective at protecting the kidneys in the treatment of diabetic proteinuric kidney disease (diabetic nephropathy).


Active ingredients

Losartan tablets contain the active ingredient losartan potassium which comes as 25 mg, 50 mg or 100 mg.

Inactive ingredients

Losartan contains the following inactive ingredients: colloidal silicon dioxide, hydroxypropyl cellulose, hypromellose, lactose anhydrous, magnesium stearate, microcrystalline cellulose, pregelatinized starch, talc and titanium dioxide.

Please note: Inactive ingredients may vary across different generic manufacturers of Losartan.

Which ingredients can cause an allergic reaction?

Losartan is a blood pressure medication that is rarely associated with causing a severe allergic reaction. While a severe allergic reaction is uncommon, you should keep an eye for it. Symptoms of a severe allergic reaction include finding it hard to breathe, a rash, dizziness and swelling of the face. It is imperative you get medical attention as soon as possible if you experience any of these symptoms after taking Losartan. 


Losartan dosage

Losartan potassium (Cozaar) is prescribed in the following dosages:

  • Losartan potassium 25 mg
  • Losartan potassium 50 mg
  • Losartan potassium 100 mg

It is begun at 25 mg and increased to a maximum of 100 mg once daily or in divided doses. It can be taken anytime but usually, the morning is best.

When is the best time to take Losartan?

The best time to take Losartan potassium is in the morning but if the side effects are bothersome, you can also take it at bedtime.

How to take Losartan

Take Losartan at the same time each day. It does not matter if it is taken with or without food. 

What should I do if I miss a dose of Losartan?

If you are still within 12 hours of the time you were due for your dose, take the dose. If it is more than 12 hours, skip the dose, and take the next dose as usual. Do not take double the dose to make up for the missed dose. 

Side Effects

Side Effects of Losartan

As with any medicine, there are many side effects of losartan potassium but most of them are recorded as minor. Some losartan side effects are;

  • Low blood pressure
  • Excess potassium
  • Headache
  • Breathlessness
  • Chest pain
  • Sore throat
  • Infections
  • Weakness
  • Dizziness
  • Elevated liver enzyme levels
  • Myalgia
  • Rashes
  • Insomnia
  • Nightmares


Do not take Losartan if any of the following apply to you.

  • Allergy to the drug
  • Pregnancy
  • Breastfeeding
  • Children under the age of 6
  • Diabetic patients taking losartan with aliskiren.


  • Liver disease
  • Kidney disease
  • Heart failure
  • Dehydration
  • Monitor blood potassium levels and avoid use along with potassium-sparing diuretics
  • Avoid driving or operating heavy machinery during treatment until the side effects are known and managed.
  • Avoid alcohol use during therapy

Drug Interactions

  • Water pills or diuretics, other antihypertensives: May lower blood pressure too much.
  • Potassium-sparing diuretics, potassium supplements: Risk of excess potassium
  • NSAIDs: May counteract the blood pressure-lowering effect of Losartan.
  • Ketoconazole: an antifungal that can increase the levels in the blood.
  • Phenobarbital: Results in 20% reduction in the effects of losartan and its active break down the product.


Disclaimer: This is not medical advice. You and your physician will determine if and how you should take any medication prescribed to you following a medical consultation.

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