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Hydrochlorothiazide, more commonly referred to as HCTZ, is a thiazide diuretic. It is most commonly used to lower high blood pressure and alleviate edema (fluid retention) from numerous causes. It is also sometimes used to reduce risk of developing kidney stones and in some other conditions.

All diuretics increase urine production, causing more frequent urination and/or a greater volume of urine. There are quite a few medications classified as diuretics, however, and not all are suitable in all cases. For high blood pressure and edema the preferred diuretics are loop diuretics and thiazide diuretics. Hydrochlorothiazide is the latter, a thiazide diuretic.

Lowering Blood Pressure with Hydrochlorothiazide

Hydrochlorothiazide is thought to be effective in lowering blood pressure in two ways; by reducing overall blood volume and by lowering vascular resistance.

The medication reduces blood volume by inhibiting salt reabsorption in the kidneys, which in turn reduces the retention of water in the blood (and elsewhere in the body), reducing overall blood volume and thus making it easier for the heart to move the blood. Hydrochlorothiazide's effect on vascular resistance is less clear.

Diuretics like hydrochlorothiazide are often the first treatment prescribed when high blood pressure is diagnosed. Sometimes diuretics alone are enough to manage the condition, but it's also very common that any single treatment is not enough to manage hypertension. If hydrochlorothiazide alone is unable to bring blood pressure down to desired levels it is very likely another type of medication, such as a beta blocker or calcium channel blocker, will be prescribed along with hydrochlorothiazide.

Treatment is fairly straightforward:

• Start with 25 mg once per day.
• If 25 mg proves insufficient after several weeks of use, dosage may be increased to 50 mg per day, taken once daily or divided into two doses.
• If 50 mg proves insufficient, there will likely be greater benefit from adding a second anti-hypertensive medication, such as a beta-blocker, rather than further increase hydrochlorothiazide dosage.

It will take several weeks of treatment for full effects to be seen, though some patients may notice improvements sooner.

Treatment with hydrochlorothiazide may continue for as long as it continues to provide benefit. If the underlying cause of the high blood pressure is not addressed, treatment may continue for the remainder of life.

Alleviating Edema with Hydrochlorothiazide

Hydrochlorothiazide reduces edema by reducing the overall volume of fluid in the body. It does so by inhibiting salt reabsorption in the kidneys; salt encourages water retention, so less salt means more water is expelled via urination.

As when the medication is used for hypertension, it is very common for additional medications to be given along with hydrochlorothiazide to further reduce edema if the diuretic alone doesn't provide sufficient relief. Some results should be noticeable in the first week or two of treatment, though it may take longer for full benefit to be seen. This depends to some extent on the cause of the edema.

For edema treatment is more variable than when hydrochlorothiazide is used for hypertension:

• Standard dosing starts with 25 mg once per day.
• If 25 mg proves insufficient, dosage may be incrementally increased to 50, 75, or 100 mg per day, taken once daily or divided into two doses.
• Some patients take doses every two or three days, rather than daily.
• With larger doses of 75 or 100 mg, some patients take a dose once every five days.

Dosage strength, frequency of administration, and duration of treatment should be individualized according to the condition, its severity, other medications being taken, and individual response to treatment. Regular checkups are strongly recommended, particularly at the start of treatment, to ensure the medication is working properly and to monitor for developing complications.