Hydrochlorothiazide uses (including “off-label” uses)

While a flashy ad on TV may make the latest prescription medication seem appealing, chances are you're not going to walk away knowing the whole story. Many prescription drugs are used to treat multiple conditions, not just the one for which they're known best. That's the case with hydrochlorothiazide (HCTZ), a thiazide diuretic (a.k.a. a "water pill") that is commonly used to treat high blood pressure.

The U.S. Food and Drug Administration (FDA) approved hydrochlorothiazide to treat high blood pressure (hypertension) (FDA, 2011). Think of your blood vessels like the pipes in your house. They're meant to carry liquid (your blood) from one place to another. But when the pressure in those pipes is high, it can cause damage to the pipes themselves or even leaks. In people with high blood pressure, the strain on their blood vessels puts them at a higher risk of heart disease and stroke (Fryar, 2012; Gaciong, 2013).

In order to lower the pressure in your blood vessels, your healthcare provider may prescribe a diuretic medication like HCTZ. These drugs work to lower blood pressure by removing water from your body in the form of urine. When your body has less water, your blood volume is lower, and there's less pressure "on the pipes," so to speak. With some exceptions, thiazide diuretics are generally the first diuretics prescribed to help lower blood pressure (Whelton, 2018). 

Thiazide diuretics such as HCTZ help the body get rid of sodium, chloride, and water, reducing fluid retention in the body. The medication acts on the kidneys, helping them lower blood pressure by getting rid of more water from your blood in the form of urine. But there are many different medications available to treat high blood pressure, including beta-blockers, ACE-inhibitors, angiotensin receptor blockers (ARBs), and calcium channel blockers. When any of these treatments alone are not enough to lower blood pressure, your healthcare provider may prescribe a combination treatment that contains both one of these drugs and HCTZ or another diuretic (Sica, 2011). 

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HCTZ is also approved by the FDA to treat swelling (edema) that's caused by congestive heart failure or kidney disease (FDA, 2011). Edema happens when a body part swells due to fluid gathering in the tissue (think of a soggy sponge that sits in the kitchen sink). It can happen in your arms or legs (peripheral edema), abdomen (ascites), or even your lungs (pulmonary edema) (Sterns, 2019). Not only is the condition uncomfortable, but it can also be dangerous. When the fluid gathers in your lungs, it can make it hard to breathe. Also, the more fluid that collects in your body, the harder it is for your heart to pump properly. 

There are certain kinds of edema associated with kidney disease and heart failure. Kidney disease may prevent the kidneys from removing enough water and sodium from the body. This increases the pressure in the blood vessels, which can lead to fluid gathering in the legs or around the eyes (Sterns, 2019). 

HCTZ may also be used off-label (in ways not specifically approved by the FDA) to prevent kidney stones (calcium nephrolithiasis) and to help people with diabetes insipidus, a rare condition in which the body loses too much water when you pee (NIH, 2019; UpToDate, n.d.). Diabetes insipidus (DI) is not the same as diabetes mellitus (high blood sugar). Patients with DI lose too much water in their urine, resulting in low blood pressure. HCTZ can be used to regulate this condition and alleviate excess water loss for these patients (Bichet, 2019). 

HCTZ can also be used to prevent the recurrence of calcium-containing kidney stones. Kidney stones form when too much calcium settles in the kidneys. One way to prevent kidneys stones is to stay hydrated. Since HCTZ tells the kidneys to remove calcium from the urine, it can be used to prevent the settlement of calcium in the kidneys and the formation of new kidney stones (Reilly, 2010). 

HCTZ isn't always the right choice for preventing future kidney stones, though. Your healthcare provider may opt for a different thiazide diuretic based on your specific health circumstances (Reilly, 2010).

HCTZ is sold as a generic drug and under the brand names Microzide, HydroDiuril, and Oretic. The generic form and brand name versions of HCTZ are available as tablets in 12.5 mg, 25 mg, and 50 mg dosages. These medications are typically taken once a day. 

When HCTZ alone isn't enough to control blood pressure, it may be used along with other blood pressure medications such as ACE-inhibitors, ARBs, calcium channel blockers, and beta-blockers (Sica, 2011). Combination drugs bundle HCTZ and one of these medications into the same tablet. Not all of these medications are available as generic drugs. These combination medications use either 12.5 mg or 25 mg dosages for the diuretic.

All forms of HCTZ, as well as the combination drugs, should be stored at room temperature out of the reach of children. In the case of a missed dose, the dose should be taken as soon as possible unless it's almost time for the next dose. In that case, only take the next dose as scheduled (NIH, 2019).

Common side effects of hydrochlorothiazide include more frequent urination, constipation or diarrhea, headache, erectile dysfunction, loss of appetite, nausea, vomiting, vision problems, and weakness. Higher doses are more likely to cause more side effects, while at doses of 12.5 mg, patients in one clinical trial experienced the same rate of side effects as those given a placebo (DailyMed, 2014).

More serious side effects are possible. Hydrochlorothiazide affects electrolyte and fluid balance in the body, which means it can dramatically alter the amount of water or certain minerals in your body. This medication may cause low sodium levels (hyponatremia), low potassium levels (hypokalemia), or low magnesium levels (hypomagnesemia). If you experience any symptoms of an electrolyte imbalance such as dry mouth, weakness, restlessness, confusion, or muscle pains, seek medical attention right away as these conditions can be life-threatening (DailyMed, 2014; NIH, 2019).

This medication may also cause high uric acid levels (hyperuricemia). The buildup of uric acid in the body can lead to a condition called gout, a painful type of arthritis characterized by sudden pain, redness, and swelling of the joints (Jin, 2012). For people with a history of gout, hydrochlorothiazide may make symptoms worse (DailyMed, 2014).

HCTZ can cause dangerously low blood pressure, a condition known as hypotension. Drinking alcohol may increase your chances of experiencing low blood pressure while taking hydrochlorothiazide. Low blood pressure symptoms include dizziness or lightheadedness, blurred vision, fatigue, shallow breathing, rapid heart rate, confusion, and fainting (DailyMed, 2014).

People with an allergy to sulfa drugs should not take HCTZ as it can cause an allergic reaction (FDA, 2011). Seek medical attention immediately if you experience any signs of an allergic reaction, such as hives, shortness of breath, trouble breathing, wheezing, skin rash, or swelling of the face, tongue, or throat. 

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Current version

October 16, 2020

Written by

Linnea Zielinski

Fact checked by

Yael Cooperman, MD

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About the medical reviewer

Yael Cooperman, MD, Ro

Yael Cooperman is a physician and works as a Senior Manager, Medical Content & Education at Ro.