What Does Losartan H Treat? A Detailed Look at the Combination Drug for Hypertension

October 8, 2025 •

4 min read

In 2023, losartan-hydrochlorothiazide was one of the most commonly prescribed medications in the United States, with over 9 million prescriptions. So, what does losartan H treat? This combination medication is primarily used to manage high blood pressure (hypertension) and prevent serious cardiovascular events.

Quick Summary

Losartan H (losartan-hydrochlorothiazide) is a combination medication for treating hypertension and lowering stroke risk in certain patients. It uses two distinct mechanisms to relax blood vessels and reduce fluid retention, effectively lowering blood pressure.

Key Points

Dual-Action Treatment: Losartan H is a combination medication containing an ARB (losartan) and a diuretic (hydrochlorothiazide) to lower blood pressure more effectively than either drug alone.
Manages Hypertension: Its primary use is to treat high blood pressure, especially when a single medication is not sufficient to achieve blood pressure goals.
Reduces Stroke Risk: It is also used to reduce the risk of stroke in patients with hypertension and left ventricular hypertrophy (enlarged heart), though this effect may not apply to Black patients.
Potential Side Effects: Common side effects include dizziness and upper respiratory infections, while more serious risks include low blood pressure, kidney problems, allergic reactions (angioedema), and electrolyte imbalance.
Critical Precautions: The medication is contraindicated during pregnancy due to fetal harm and requires monitoring of kidney function, electrolyte levels, and potential interactions with NSAIDs, potassium, and lithium.
Regular Monitoring is Key: Because it can affect kidney function and electrolyte balance, regular blood tests are necessary to ensure safe and effective use.

What is Losartan H?

Losartan H is a combination medication containing two active ingredients: losartan and hydrochlorothiazide. Losartan is an angiotensin II receptor blocker (ARB), and hydrochlorothiazide is a thiazide diuretic, often referred to as a "water pill". The medication is available as an oral tablet and is also known by the brand name Hyzaar. This dual-action approach allows for a more potent blood pressure-lowering effect than either drug could achieve alone.

Primary Medical Uses

The combination of losartan and hydrochlorothiazide is prescribed for specific medical conditions, primarily related to cardiovascular health. Your doctor will determine if this medication is the right choice based on your individual health needs.

Treating Hypertension

The most common and primary use for losartan H is to treat high blood pressure, or hypertension. When left untreated, high blood pressure can strain the heart and arteries, potentially leading to long-term damage to the brain, heart, and kidneys. A doctor may prescribe this combination drug for a patient whose blood pressure is not adequately controlled with losartan alone or another monotherapy. Lowering blood pressure helps reduce the risk of more serious health issues, such as heart attack, heart failure, and kidney disease.

Reducing the Risk of Stroke

Losartan H is also indicated to lower the risk of stroke in patients who have both hypertension and left ventricular hypertrophy (LVH), which is an enlargement of the heart muscle. The medication helps by inhibiting the effects of angiotensin II, which can cause the heart to remodel and thicken. However, it is important to note that studies suggest this benefit may not apply to Black patients with these conditions.

Mechanism of Action: How Losartan H Works

Losartan H's effectiveness comes from the combined action of its two components, which target different mechanisms in the body to control blood pressure.

Losartan: This is an angiotensin II receptor blocker (ARB). It works by blocking the action of a naturally occurring substance called angiotensin II, which causes blood vessels to constrict and narrow. By blocking the angiotensin II receptors, losartan helps relax and widen the blood vessels, allowing blood to flow more easily and thereby lowering blood pressure.
Hydrochlorothiazide (HCTZ): This is a thiazide diuretic, or a "water pill". It acts on the kidneys, increasing the excretion of sodium and water from the body through urine. This reduction in fluid volume helps lower blood pressure and eases the workload on the heart.

The combination of these two mechanisms provides a more comprehensive and effective reduction in blood pressure than either medication on its own. It’s a classic example of synergy in pharmacology, where the combined effect is greater than the sum of the individual parts.

Comparing Losartan H vs. Losartan Alone

For patients with hypertension, a physician may choose between losartan alone (monotherapy) and the losartan-hydrochlorothiazide combination. The decision is based on the severity of the hypertension and the patient's response to initial treatment.


Feature	Losartan Alone (e.g., Cozaar)	Losartan H (losartan/HCTZ, e.g., Hyzaar)
Drug Class	Angiotensin II Receptor Blocker (ARB)	Combination of an ARB and a Thiazide Diuretic
Mechanism of Action	Blocks angiotensin II, relaxing blood vessels	Blocks angiotensin II AND removes excess salt and water
Efficacy in Lowering BP	Effective for mild to moderate hypertension	More potent effect, useful when losartan monotherapy is insufficient
Primary Uses	Hypertension; stroke risk reduction (in specific populations); diabetic nephropathy	Hypertension (especially if monotherapy is insufficient); stroke risk reduction (in specific populations)
Effect on Potassium	Can cause hyperkalemia (high potassium)	Counteracts the potassium-retaining effect of losartan; can cause hypokalemia (low potassium) or hyperkalemia
Contraindications	Pregnancy	Pregnancy; anuria; concurrent use with aliskiren in diabetes

Side Effects and Warnings

As with any medication, losartan H can cause side effects. Some are common and mild, while others are more serious and require immediate medical attention. It is crucial to report any persistent or severe side effects to your doctor.

Common Side Effects

Dizziness or lightheadedness, especially when standing up
Upper respiratory tract infection
Headache
Back pain

Serious Side Effects

Low Blood Pressure (Hypotension): Can cause fainting or severe dizziness.
Kidney Injury: Monitor kidney function, especially in individuals with existing kidney problems.
Allergic Reaction (Angioedema): Swelling of the face, lips, tongue, or throat, which can be life-threatening.
Electrolyte Imbalance: The diuretic component can cause changes in potassium, sodium, and magnesium levels.
Fetal Toxicity: Losartan H is contraindicated during pregnancy as it can cause harm or death to an unborn baby.
Risk of Skin Cancer: Hydrochlorothiazide is associated with an increased risk of non-melanoma skin cancer with long-term, high-dose use.

Contraindications and Interactions

Several conditions and medications can interact with losartan H, so it's essential to inform your healthcare provider of your full medical history and all medications you take.

Pregnancy: Use during pregnancy is strictly prohibited due to severe fetal risks.
Anuria: This medication should not be used in patients who are unable to produce urine.
Drug Interactions: Use caution with potassium supplements, NSAIDs, lithium, and certain other blood pressure medications like aliskiren.
Surgical Procedures: Inform your surgeon or dentist that you are taking this medication before any procedure.

Conclusion: The Benefits of Combination Therapy

Losartan H is a valuable medication for managing hypertension and reducing the risk of stroke in specific patient populations. By combining an angiotensin II receptor blocker with a diuretic, it offers a more effective approach to lowering blood pressure than single-ingredient treatments. However, patients must be aware of the potential side effects and the importance of regular monitoring by a healthcare provider, especially concerning kidney function and electrolyte levels. As with any prescription, it is crucial to take the medication exactly as directed and maintain open communication with your doctor.

For more detailed, clinical information, consult reputable sources such as the National Institutes of Health or discuss with your healthcare provider.

Frequently Asked Questions

The primary function of losartan H is to treat high blood pressure (hypertension) by combining two different medications: losartan, which relaxes blood vessels, and hydrochlorothiazide, which removes excess fluid and salt from the body.

Losartan H, which is the combination of losartan and hydrochlorothiazide, is commonly sold under the brand name Hyzaar. It is also available as a generic medication.

No, losartan H should not be used during pregnancy. It can cause serious harm, or even death, to an unborn baby, particularly if taken during the second and third trimesters.

If you feel dizzy or lightheaded, you should sit or lie down slowly to prevent fainting. Dizziness is more common when starting the medication or increasing the dose. If it persists or is severe, contact your doctor.

You should avoid potassium supplements or salt substitutes containing potassium, unless advised by your doctor, as losartan can affect potassium levels. High-salt diets can also decrease the medication's effectiveness.

Your blood pressure will need to be checked regularly by your healthcare provider to monitor the medication's effectiveness. Additionally, your doctor will periodically order blood tests to check your electrolyte levels and kidney function.

In many cases, yes. The combination of losartan and hydrochlorothiazide provides a greater reduction in blood pressure than losartan alone. This makes it a preferred option for patients whose hypertension is not adequately controlled with losartan monotherapy.