Hydrochlorothiazide: uses and side effects

Hydrochlorothiazide (HCTZ) is a diuretic, which is a type of medication that increases how much you pee. Used to reduce fluid retention in the body and lower blood pressure, diuretics such as HCTZ help the body get rid of sodium and chloride as well as water in the form of urine.

The U.S. Food and Drug Administration (FDA) approved hydrochlorothiazide to treat high blood pressure as well as swelling (edema) that’s caused by congestive heart failure or kidney disease (FDA, 2011). By acting on the kidneys, HCTZ helps them lower blood pressure by getting rid of excess water from your blood and releasing it into the urine. Reducing water retention in the body also alleviates edema, which happens when a body part swells due to fluid gathering in the tissue (Sterns, 2019). 

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Swelling (edema) can happen in your arms or legs (peripheral edema), or even your lungs (pulmonary edema) (Sterns, 2018).

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, 2018). 

In individuals with congestive heart failure, the heart is too weak to pump the blood properly around the body. If the left side of the heart is too weak to move blood out of the lungs and back out into the body, blood pools around the lungs. This may cause the lungs to swell and become spongy (like if you let a loaf of bread soak up water), which is called pulmonary edema, and it can be life-threatening (Sterns, 2018).

Thiazide diuretics such as HCTZ help the body get rid of sodium, chloride, and water, reducing water retention in the body. Hydrochlorothiazide acts on the kidneys, helping them lower blood pressure by getting rid of more or less water from your blood as urine. 

Blood pressure is the amount of pressure put on the walls of your blood vessels. In people with high blood pressure (hypertension), the strain on their blood vessels puts them at a higher risk of heart disease (cardiovascular disease) and stroke (Fryar, 2012; Gaciong, 2013). 

Thiazide diuretics such as HCTZ are generally the first diuretics prescribed to help lower blood pressure, except for patients with chronic kidney disease (CKD), but they’re just one type of diuretic (Whelton, 2018). 

In some cases, diuretics alone aren’t enough to lower blood pressure. If that happens, diuretics such as HCTZ may safely be combined with other blood pressure medications, including beta-blockers, ACE inhibitors, angiotensin receptor blockers (ARBs), and calcium channel blockers (Sica, 2011).

Medications can also be used “off-label” or to treat conditions for which they don’t specifically have FDA approval. 

HCTZ is used off-label by healthcare professionals to prevent kidney stones (NIH, 2019). These stones may form when too much calcium gets into the urine and combines with other minerals and salts. HCTZ can help prevent their formation by stopping your kidneys from releasing calcium into the urine. If there’s less calcium in your urine, there’s a lower chance that kidney stones will form (UpToDate, n.d.).

Hydrochlorothiazide can also help people with diabetes insipidus (DI), a medical condition characterized by a fluid and salt imbalance in the body (UpToDate, n.d.). This condition is not the same as diabetes mellitus (high blood sugar). Patients with DI lose too much water in their urine. HCTZ can be used to reduce excess water loss in these patients in order to regulate this condition (Bichet, 2019). 

Due to the way HCTZ acts in the body and affects electrolyte and fluid balance as well as blood pressure, serious side effects are possible. More frequent urination, constipation or diarrhea, headache, erectile dysfunction, loss of appetite, nausea, vomiting, vision problems, and weakness are common side effects of hydrochlorothiazide (DailyMed, 2014).

These side effects may be dose-dependent. Patients taking doses of 25 mg or higher in clinical trials experienced adverse effects more frequently than those on lower doses. Individuals taking 12.5 mg (the lowest dose available) experienced the same rate of side effects as those given a placebo (DailyMed, 2014).

In some cases, HCTZ’s effect on blood pressure can cause dangerously low blood pressure, a condition known as hypotension. Low blood pressure symptoms include dizziness, blurred vision, fatigue, shallow breathing, rapid heart rate, confusion, and fainting. Talk to your pharmacist or healthcare provider before drinking alcohol while taking HCTZ, as combining them may increase your chances of experiencing low blood pressure (DailyMed, 2014).

Hydrochlorothiazide may also cause high uric acid levels (hyperuricemia), which may lead to the development of gout. Gout is a painful type of arthritis marked by “attacks,” sudden onset of pain, redness, and swelling of the joints (Jin, 2012). In those with gout, HCTZ may bring on an attack or make symptoms worse (DailyMed, 2014).

Serious side effects

Hydrochlorothiazide may cause electrolyte imbalances, which may cause serious complications. HCTZ can cause low sodium levels (hyponatremia), low potassium levels (hypokalemia), and low magnesium levels (hypomagnesemia). 

Symptoms of electrolyte imbalances include dry mouth, irregular heartbeats (arrhythmias), muscle aches, nausea, thirst, tiredness, vomiting, and weakness. In some cases, these conditions can be dangerous and even life-threatening (DailyMed, 2014). If you experience any of these signs of an electrolyte imbalance such as dry mouth, weakness, restlessness, confusion, or muscle pains, seek medical help right away (NIH, 2019).

People who have an allergy to sulfa drugs should not use hydrochlorothiazide as it can cause a serious allergic reaction (FDA, 2011). An allergic reaction may cause hives, shortness of breath, trouble breathing, wheezing, skin rash, or swelling of the face, tongue, or throat. Seek medical attention immediately if you experience any of these signs of an allergic reaction. 

Hydrochlorothiazide is available as a generic drug as well as brand-name medications Microzide, HydroDiuril, and Oretic. HCTZ alone may not be enough to lower high blood pressure adequately.

In these cases, combination drugs that bundle HCTZ and another blood pressure medicine into one tablet may be used. ACE inhibitors, ARBs, calcium-channel blockers, beta-blockers, and antiadrenergic medicines are all prescription drugs that can safely be combined with HCTZ (Sica, 2011). HCTZ is also combined with potassium-sparing diuretics like triamterene to avoid low blood potassium levels.

Talk to a pharmacist or healthcare professional if you feel you need to take painkillers while on HCTZ or any of these combination drugs. Non-steroidal anti-inflammatory drugs (NSAIDs) may decrease how effectively HCTZ lowers your blood pressure (FDA, 2011). This includes over-the-counter options like naproxen (brand names Aleve and Midol) and ibuprofen (brand names Motrin and Advil) and prescription medications such as indomethacin.

Check the prescription label and get medical advice about the drug information you need to know for these combination medicines, including potential side effects and drug interactions.

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Current version

November 02, 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.