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Important things to know about losartan hydrochlorothiazide

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This combo medication can bring down blood pressure if other hypertension treatments aren’t doing the trick.
Written by Emily Shiffer
Updated on December 21, 2022

Reducing high blood pressure (also known as hypertension) is super important. Almost half of all adults in the U.S. have high blood pressure, according to the Centers for Disease Control and Prevention (CDC). And only 1 in 4 of them have it under control. That’s a lot of folks who are at risk of heart attacks and strokes.

But getting your blood pressure down to normal levels isn’t always easy. What works for friends and family might not work for you. And that’s okay. Luckily, there are many medications that manage high blood pressure.

One of these is losartan hydrochlorothiazide (Hyzaar®). It’s a combination medication that people take when other medications haven’t brought down their blood pressure far enough, says Elizabeth Klodas, MD. She’s a cardiologist and founder of Step One Foods, a company that makes heart-healthy meals and snacks.

If you’re about to start losartan hydrochlorothiazide, you probably have questions. Here’s everything you need to know, from how it works to any side effects.

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How does losartan hydrochlorothiazide work?

Losartan hydrochlorothiazide is a combination of 2 medications in 1 tablet. The medications work in separate ways to accomplish a single goal — lowering your blood pressure, explains Alyssa Wozniak, PharmD. She’s a clinical assistant professor at D’Youville School of Pharmacy in Buffalo, New York.

Losartan (Cozaar®) is an angiotensin II receptor blocker. Your body releases angiotensin II to tighten blood vessels. When blood vessels tighten, your blood pressure goes up. Losartan blocks that action from happening.

Hydrochlorothiazide is a diuretic, or water pill. It causes the kidneys to release more sodium and water when you go to the bathroom. And that lowers your blood pressure, too.

Doctors also prescribe these 2 medications separately. Or your doctor may have started you on one of them and then decided to add the other. Typically, people end up taking the 2 together because losartan or hydrochlorothiazide alone wasn’t enough to control blood pressure, explains Dr. Klodas.

Who should take losartan hydrochlorothiazide?

There are many reasons that doctors prescribe this medication, including:

  • You have stage 2 hypertension. That means your blood pressure is 140/90 mm Hg or higher.
  • You also have heart disease, such as an enlarged heart or heart failure. Or you’re at a high risk of having a stroke.
  • You already take losartan because you have kidney disease. When your doctor adds hydrochlorothiazide for blood pressure, you end up taking the 2 medications. So it’s easier to take them both in a single tablet.

Who shouldn’t take losartan hydrochlorothiazide?

Anyone who’s pregnant. Losartan can damage the fetus, Wozniak explains. If you become pregnant, stop the medication as soon as possible. Reach out to your doctor to see what other medication you can take, she suggests.

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How to take losartan hydrochlorothiazide

Your doctor will probably start you on 1 tablet a day. Take it with or without food, your choice. Just be sure to swallow the tablet. Don’t crush or chew it.

Keep taking the medication until your doctor tells you to stop, even if you feel well, Wozniak advises. High blood pressure usually doesn’t have symptoms. And it can’t be cured — just managed.

Also, keep up with diet and exercise. Remember, medications work best when you combine them with healthy habits.

Recommended reading: 16 little ways to lower your blood pressure.

Side effects of losartan hydrochlorothiazide

People usually don’t have many side effects with this medication, says Dr. Klodas. The main ones are dizziness and lightheadedness, she notes. Occasionally, people with poor blood flow to the kidneys may see their kidney function deteriorate.

Some people can be allergic to this treatment. This is especially the case for people who are allergic to sulfonamide (sulfa) medications, says Wozniak. These medications are used for bacterial infections such as urinary tract infections (UTIs). Talk about any previous allergic reactions with your doctor.

The 2 parts of the medication can cause different side effects.


  • It affects blood flow to the kidneys and raises potassium levels. So the kidneys may not work as well. High potassium levels in the blood can cause serious heart problems.
  • It can cause angioedema, which is swelling under the skin. It’s rare. But if your lips, tongue or face swells, call the doctor immediately, says Wozniak.


  • This can lower potassium levels in the blood. That can lead to muscle cramps or weakness, constipation, uneven heartbeats, fatigue and dizziness.
  • It can make you more sensitive to sunlight, says Wozniak. It can also worsen gout if you have it (or have had it).
  • It can raise blood sugar levels, although the effect is slight, says Dr. Klodas.

Because of these side effects, you’ll have a blood test before you start losartan hydrochlorothiazide. That gives your provider a chance to check potassium levels. They’ll also see how well your kidneys work. If you get the green light, expect more blood tests. This is how your doctor will keep an eye on potassium levels and kidney function moving forward.

Taking losartan hydrochlorothiazide might just be the treatment you need. And you can rest easy knowing that you’ve taken a big step toward keeping healthy.

(No matter how you manage your high blood pressure, Optum Perks wants to help you save at the pharmacy. Here’s how it works.)

Additional sources:
Blood pressure facts: Centers for Disease Control and Prevention
New guidelines for blood pressure: American Heart Association
Stroke risk: European Cardiology Review (2019). “Hypertension and Stroke: Update on Treatment”