What Is HCTZ?

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  • Written By: Clara Kedrek
  • Edited By: Jessica Seminara
  • Last Modified Date: 05 November 2019
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Hydrochlorothiazide (HCTZ) is a pharmaceutical agent used to treat a number of medical conditions. It works as a diuretic, and increases the amount of urine produced by patients. Although most commonly used to treat hypertension — or high blood pressure — it can also be used to treat fluid retention and low blood calcium levels. Side effects of the medication can include dizziness, dehydration, and headache. Patients allergic to sulfa medications, or those with certain underlying medical conditions, should take caution in using this medication.

HCTZ exerts its effects on the body by altering the function of the kidneys. It blocks one of the channels that usually allows sodium and chloride to be reabsorbed from the urine back into the blood. Without the action of this channel, patients have increased urination and a net loss of electrolytes such as sodium, potassium, and chloride from their bodies. Many patients call HCTZ a "water pill" because it increases their urination; the medical term for this type of drug is a diuretic. This medication is typically given in pill form, and goes by the brand names Esidrix® and Microzide®.


The main use of HCTZ is to treat hypertension. It helps to decrease the pressure within the body's vasculature by decreasing the amount of fluid in the body. Many doctors consider this medication to be a first-line option for treating high blood pressure because it is cheap, effective, and well tolerated by many patients. Often hydrochlorothiazide is combined with other anti-hypertensive medications, such as drugs in the angiotensin-converting enzyme (ACE) inhibitor class, as a once-daily combination pill.

Although mainly used to treat high blood pressure, HCTZ can also treat other conditions. In patients who have swelling in their feet or hands, the medication can be used to reduce this fluid retention. Those with low blood levels of calcium can take the medication in order to increase the concentration of this mineral in their blood.

Common side effects of HCTZ include dehydration, diarrhea, headache, abdominal pain, dizziness, and rash. The medication often causes alterations in the electrolyte levels of the blood, resulting in low levels of potassium, chloride, and magnesium. It can also raise the level of calcium in the blood, which can make patients prone to kidney stones. This medication can also increase glucose and lipid levels in the blood.

Not all patients are good candidates for treatment with HCTZ. It is considered to be a member of the sulfa class of medications, so patients with sulfa allergies should not take this drug. Patients with gout are advised to avoid HCTZ because it could trigger attacks of joint pain. This medication should also be avoided in patients with poor renal function, diabetes mellitus, dehydration, or liver disease because they could experience more severe side effects.


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