Hydrochlorothiazide dosage: what’s right for me?

Working with a healthcare provider to treat a condition is a little like working with a golf instructor. They know what iron you need to use to get the job done (that's the medicine you're prescribed) and exactly how hard you'll need to hit the ball to reach the green (that's the dose of this medication they'll select). If you've recently been prescribed hydrochlorothiazide (HCTZ), here's what you need to know about the drug, its dosages, and how it works.

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

Hydrochlorothiazide is available as a generic drug or under the brand names Microzide and Oretic. Each of these versions is available as tablets in 12.5 mg, 25 mg, and 50 mg dosages that 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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Hydrochlorothiazide is a prescription diuretic medication (a.k.a. a "water pill") used to treat high blood pressure (hypertension). There are a bunch of different types of diuretics that differ based on how they work in the kidneys. HCTZ is a thiazide diuretic, and it works by helping your kidneys get rid of sodium, chloride, and water through the urine, reducing water retention and lowering blood pressure.

While there are several types of diuretics, thiazide diuretics are generally the first diuretics prescribed to help lower blood pressure, except in patients with chronic kidney disease (CKD) (Whelton, 2018).

How is hydrochlorothiazide used?

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).

Diuretics such as HCTZ can be combined with other prescription drugs safely to further lower blood pressure. Research has shown that thiazide diuretics may be used in combination with prescription medications such as beta-blockers, ACE inhibitors, angiotensin receptor blockers (ARBs), and calcium channel blockers (Sica, 2011). This is why some prescription drugs have these blood pressure medicines and diuretics, such as HCTZ, in the same tablet.

Since HCTZ causes your body to release excess water through your urine, patients taking this medication typically experience increased frequency of urination, especially when they just start treatment. Other common side effects of hydrochlorothiazide include 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. Adverse effects happened more frequently in those taking doses of 25 mg or more in clinical trials. Individuals taking a lower dose (12.5 mg) experienced the same rate of side effects as those given a placebo (DailyMed, 2014).

This medication may also cause high uric acid levels (hyperuricemia). The buildup of uric acid in the body can lead to the development of 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 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, confusion, and fainting. Drinking alcohol may increase your chances of experiencing low blood pressure while taking hydrochlorothiazide (DailyMed, 2014).

Serious side effects

Because HCTZ changes the balance of electrolytes in your body (altering levels of substances like magnesium, potassium, calcium, and sodium), it can sometimes cause an imbalance in these substances. 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). If you experience any symptoms of an electrolyte imbalance such as dry mouth, weakness, restlessness, confusion, or muscle pains, seek medical attention immediately (NIH, 2019).

It is possible for people to have an allergic reaction to HCTZ (FDA, 2011). This diuretic is a sulfonamide, a medication that contains sulfa, so people with an allergy to sulfa drugs should not take hydrochlorothiazide. 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.

Always take your medications as directed. If you experience unfavorable side effects, or if you are interested in changing medications or dosages, contact your healthcare provider. 

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

October 19, 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.