Hydrochlorothiazide: common and serious side effects

A "water pill" sounds relatively harmless, but prescription diuretics like hydrochlorothiazide (HCTZ) are prescription medications. These diuretics have more potential side effects than simply making you urinate more, and you should be aware of them—as well as the potential benefits these medications offer—if you're talking to your healthcare provider about HCTZ.

Hydrochlorothiazide is a thiazide diuretic (or "water pill") used to treat high blood pressure or swelling by helping your body get rid of excess water, sodium, and chloride.

Common side effects of hydrochlorothiazide include more frequent urination, constipation or diarrhea, headache, erectile dysfunction, loss of appetite, nausea, vomiting, vision problems, and weakness, and higher doses are more likely to cause more side effects, past research has found. Adverse effects happened more frequently in those taking doses of 25mg or more in clinical trials. Individuals taking a lower dose (12.5mg) experienced the same rate of side effects as those given a placebo (DailyMed, 2014).

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This medication may also cause high uric acid levels (hyperuricemia). The buildup of uric acid in the body can lead to the development of 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 precipitate an attack (DailyMed, 2014).

Since hydrochlorothiazide is used to lower blood high blood pressure, in some cases, it can cause dangerously low blood pressure, a condition known as hypotension. Symptoms of low blood pressure include dizziness, blurred vision, fatigue, shallow breathing, rapid heart rate, and confusion, and fainting. Drinking alcohol may increase your chances of experiencing low blood pressure while taking hydrochlorothiazide (DailyMed, 2014).

People taking hydrochlorothiazide may also experience kidney problems, or, in rare cases, liver problems. These liver problems may cause jaundice, a yellowing of the skin and whites of the eyes (NIH, 2017).

Serious side effects

Hydrochlorothiazide affects electrolyte and fluid balance in the body, which can cause serious side effects. This medication may cause low sodium levels (hyponatremia), low potassium levels (hypokalemia), and low magnesium levels (hypomagnesemia). Electrolyte imbalances can cause 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). Low potassium levels can also increase blood sugar, something that can be particularly problematic for patients with diabetes (Sica, 2011).

If you experience any symptoms of an electrolyte imbalance such as dry mouth, weakness, restlessness, confusion, or muscle pains, seek medical help right away. You should also get medical attention if you notice blistering or peeling skin, fever, sore throat, chills, visual changes, or unusual bleeding or bruising (NIH, 2019).

Some people may have an allergic reaction to hydrochlorothiazide (FDA, 2011). People who have experienced a sulfa drug allergy should not take this medication. 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, which is sold under the brand names Microzide and Oretic, is a prescription medication used to treat high blood pressure (also called an antihypertensive). It is a thiazide diuretic (a.k.a. a "water pill"), a type of medication that also includes the drug chlorothiazide. These drugs help you get rid of excess salt and water by acting on the kidneys, which help control blood pressure by getting rid of more or less water from your blood in the form of urine. Hydrochlorothiazide helps the body get rid of sodium, chloride, and water, which can also help reduce water retention in the body. 

Thiazide diuretics are just one of many types of diuretics. There are several types of diuretics, and each of these types acts on the kidneys in different ways to reduce the amount of water in the body. Thiazide diuretics are generally the first diuretics prescribed to help lower blood pressure, except for patients with chronic kidney disease (CKD). These individuals may be given loop-acting diuretics instead (Whelton, 2018).

How is hydrochlorothiazide used?

Hydrochlorothiazide is approved by the U.S. Food and Drug Administration (FDA) to treat high blood pressure as well as swelling (edema) that's caused by congestive heart failure or kidney disease (FDA, 2011).

Diuretics can be combined with other prescription drugs safely to further lower blood pressure. Research has shown that thiazide diuretics may be used in conjunction with beta-blockers, ACE inhibitors, angiotensin receptor blockers (ARBs), and calcium channel blockers (Sica, 2011). 

HCTZ may also be used off-label to prevent kidney stones and to help people with diabetes insipidus, a medical condition characterized by an imbalance of salts and fluids in the body (MedlinePlus, 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).

Hydrochlorothiazide is available as a generic drug or as the brand name medications Microzide and Oretic. Each of these versions is available as tablets in 12.5mg, 25mg, and 50mg dosages. These medications are typically taken once a day. You may also find HCTZ combined with other blood pressure medications (like amlodipine, lisinopril, valsartan) in the same pill. 

This medication 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).

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Current version

September 14, 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.